Vlib/snap.c

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/*!
 * \file lib/vector/Vlib/snap.c
 *
 * \brief Vector library - Clean vector map (snap lines)
 *
 * Higher level functions for reading/writing/manipulating vectors.
 *
 * (C) 2001-2009 by the GRASS Development Team
 *
 * This program is free software under the GNU General Public License
 * (>=v2).  Read the file COPYING that comes with GRASS for details.
 *
 * \author Radim Blazek
 * \author update to GRASS 7 Markus Metz
 */

#include <stdlib.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <math.h>
#include <grass/vector.h>
#include <grass/glocale.h>
#include <grass/kdtree.h>

/* translate segment to box and back */
#define X1W 0x01        /* x1 is West, x2 East */
#define Y1S 0x02        /* y1 is South, y2 North */
#define Z1B 0x04        /* z1 is Bottom, z2 Top */

/* Vertex */
typedef struct
{
    double x, y, z;
    int anchor;                 /* 0 - anchor, do not snap this point, that means snap others to this */
    /* >0  - index of anchor to which snap this point */
    /* -1  - init value */
} XPNT;

typedef struct
{
    int anchor;
    double along;
} NEW;

/* for qsort */
static int sort_new(const void *pa, const void *pb)
{
    NEW *p1 = (NEW *) pa;
    NEW *p2 = (NEW *) pb;

    return (p1->along < p2->along ? -1 : (p1->along > p2->along));

    /*
    if (p1->along < p2->along)
        return -1;
    if (p1->along > p2->along)
        return 1;
    return 1;
    */
}

typedef struct
{
    double x, y, z, along;
} NEW2;

/* for qsort */
static int sort_new2(const void *pa, const void *pb)
{
    NEW2 *p1 = (NEW2 *) pa;
    NEW2 *p2 = (NEW2 *) pb;

    return (p1->along < p2->along ? -1 : (p1->along > p2->along));
}

/* This function is called by RTreeSearch() to find a vertex */
static int find_item(int id, const struct RTree_Rect *rect, void *list)
{
    G_ilist_add((struct ilist *)list, id);
    return 0;
}

/* This function is called by RTreeSearch() to add selected node/line/area/isle to the list */
static int add_item(int id, const struct RTree_Rect *rect, void *list)
{
    G_ilist_add((struct ilist *)list, id);
    return 1;
}

/* This function is called by RTreeSearch() to add selected node/line/area/isle to the list */
static int find_item_box(int id, const struct RTree_Rect *rect, void *list)
{
    struct bound_box box;

    box.W = rect->boundary[0];
    box.S = rect->boundary[1];
    box.B = rect->boundary[2];
    box.E = rect->boundary[3];
    box.N = rect->boundary[4];
    box.T = rect->boundary[5];

    dig_boxlist_add((struct boxlist *)list, id, &box);

    return 0;
}

/* This function is called by RTreeSearch() to add selected node/line/area/isle to the list */
static int add_item_box(int id, const struct RTree_Rect *rect, void *list)
{
    struct bound_box box;

    box.W = rect->boundary[0];
    box.S = rect->boundary[1];
    box.B = rect->boundary[2];
    box.E = rect->boundary[3];
    box.N = rect->boundary[4];
    box.T = rect->boundary[5];

    dig_boxlist_add((struct boxlist *)list, id, &box);

    return 1;
}

static void
Vect_snap_lines_list_rtree(struct Map_info *, const struct ilist *,
                           double, struct Map_info *);

static void
Vect_snap_lines_list_kdtree(struct Map_info *, const struct ilist *,
                            double, struct Map_info *);

/*!
   \brief Snap selected lines to existing vertex in threshold.
   
   Snap selected lines to existing vertices of other selected lines.
   3D snapping is not supported.
   
   Lines showing how vertices were snapped may be optionally written to error map. 
   Input map must be opened on level 2 for update at least on GV_BUILD_BASE.
   
   As mentioned above, lines are not necessarily snapped to nearest vertex! For example:
   <pre>
    |                    
    | 1         line 3 is snapped to line 1,
    |           then line 2 is not snapped to common node at lines 1 and 3,
    because it is already outside of threshold
    ----------- 3   

    |
    | 2
    |    
   </pre>
   
   The algorithm selects anchor vertices and snaps non-anchor vertices
   to these anchors.
   The distance between anchor vertices is always > threshold.
   If there is more than one anchor vertex within threshold around a
   non-anchor vertex, this vertex is snapped to the nearest anchor
   vertex within threshold.

   \param Map input map where vertices will be snapped
   \param List_lines list of lines to snap
   \param thresh threshold in which snap vertices
   \param[out] Err vector map where lines representing snap are written or NULL
   
   \return void
*/
void
Vect_snap_lines_list(struct Map_info *Map, const struct ilist *List_lines,
                     double thresh, struct Map_info *Err)
{
    if (getenv("GRASS_VECTOR_LOWMEM"))
        Vect_snap_lines_list_rtree(Map, List_lines, thresh, Err);
    else
        Vect_snap_lines_list_kdtree(Map, List_lines, thresh, Err);
}

static void
Vect_snap_lines_list_kdtree(struct Map_info *Map, const struct ilist *List_lines,
                     double thresh, struct Map_info *Err)
{
    struct line_pnts *Points, *NPoints;
    struct line_cats *Cats;
    int line, ltype, line_idx;
    double thresh2;

    int point;                  /* index in points array */
    int nanchors, ntosnap;      /* number of anchors and number of points to be snapped */
    int nsnapped, ncreated;     /* number of snapped verices, number of new vertices (on segments) */
    int apoints, npoints, nvertices;    /* number of allocated points, registered points, vertices */
    XPNT *XPnts;                /* Array of points */
    NEW *New = NULL;            /* Array of new points */
    int anew = 0, nnew;         /* allocated new points , number of new points */
    struct ilist *List;
    int *Index = NULL;          /* indexes of anchors for vertices */
    int aindex = 0;             /* allocated Index */

    struct kdtree *KDTree;
    double c[2];
    double *kdd;
    int *kduid, kd_found;


    if (List_lines->n_values < 1)
        return;

    Points = Vect_new_line_struct();
    NPoints = Vect_new_line_struct();
    Cats = Vect_new_cats_struct();
    List = Vect_new_list();

    KDTree = kdtree_create(2, NULL);

    thresh2 = thresh * thresh;

    /* Go through all lines in vector, and add each point to structure of points */
    apoints = 0;
    point = 1;                  /* index starts from 1 ! */
    nvertices = 0;
    XPnts = NULL;

    G_important_message(_("Snap vertices Pass 1: select points"));
    for (line_idx = 0; line_idx < List_lines->n_values; line_idx++) {
        int v;

        G_percent(line_idx, List_lines->n_values, 2);

        line = List_lines->value[line_idx];

        G_debug(3, "line =  %d", line);
        if (!Vect_line_alive(Map, line))
            continue;

        ltype = Vect_read_line(Map, Points, Cats, line);

        for (v = 0; v < Points->n_points; v++) {

            G_debug(3, "  vertex v = %d", v);
            nvertices++;

            /* coords */
            c[0] = Points->x[v];
            c[1] = Points->y[v];

            if (kdtree_insert(KDTree, c, point, 0)) {
                /* Add to structure */
                if ((point - 1) == apoints) {
                    apoints += 10000;
                    XPnts =
                        (XPNT *) G_realloc(XPnts,
                                           (apoints + 1) * sizeof(XPNT));
                }
                XPnts[point].x = Points->x[v];
                XPnts[point].y = Points->y[v];
                XPnts[point].anchor = -1;
                point++;
            }
        }
    }
    G_percent(line_idx, List_lines->n_values, 2); /* finish it */

    npoints = point - 1;

    /* Go through all registered points and if not yet marked mark it as anchor and assign this anchor
     * to all not yet marked points in threshold */

    G_important_message(_("Snap vertices Pass 2: assign anchor vertices"));

    nanchors = ntosnap = 0;
    for (point = 1; point <= npoints; point++) {
        int i;

        G_percent(point, npoints, 4);

        G_debug(3, "  point = %d", point);

        if (XPnts[point].anchor >= 0)
            continue;

        XPnts[point].anchor = 0;        /* make it anchor */
        nanchors++;

        /* Find points in threshold */
        c[0] = XPnts[point].x;
        c[1] = XPnts[point].y;

        Vect_reset_list(List);
        kd_found = kdtree_dnn(KDTree, c, &kduid, &kdd, thresh, &point);
        G_debug(4, "  %d points in threshold box", kd_found);

        for (i = 0; i < kd_found; i++) {
            int pointb;
            double dx, dy, dist2;

            pointb = kduid[i];
            if (pointb == point)
                continue;

            dx = XPnts[pointb].x - XPnts[point].x;
            dy = XPnts[pointb].y - XPnts[point].y;
            dist2 = dx * dx + dy * dy;

            if (dist2 > thresh2) /* outside threshold */
                continue;
                
            /* doesn't have an anchor yet */
            if (XPnts[pointb].anchor == -1) {
                XPnts[pointb].anchor = point;
                ntosnap++;
            }
            else if (XPnts[pointb].anchor > 0) {   /* check distance to previously assigned anchor */
                double dist2_a;

                dx = XPnts[XPnts[pointb].anchor].x - XPnts[pointb].x;
                dy = XPnts[XPnts[pointb].anchor].y - XPnts[pointb].y;
                dist2_a = dx * dx + dy * dy;

                /* replace old anchor */
                if (dist2 < dist2_a) {
                    XPnts[pointb].anchor = point;
                }
            }
        }
        if (kd_found) {
            G_free(kdd);
            G_free(kduid);
        }
    }

    /* Go through all lines and: 
     *   1) for all vertices: if not anchor snap it to its anchor
     *   2) for all segments: snap it to all anchors in threshold (except anchors of vertices of course) */

    nsnapped = ncreated = 0;

    G_important_message(_("Snap vertices Pass 3: snap to assigned points"));

    for (line_idx = 0; line_idx < List_lines->n_values; line_idx++) {
        int v, spoint, anchor;
        int changed = 0;
        double kddist;

        G_percent(line_idx, List_lines->n_values, 2);

        line = List_lines->value[line_idx];

        G_debug(3, "line =  %d", line);
        if (!Vect_line_alive(Map, line))
            continue;

        ltype = Vect_read_line(Map, Points, Cats, line);

        if (Points->n_points >= aindex) {
            aindex = Points->n_points;
            Index = (int *)G_realloc(Index, aindex * sizeof(int));
        }

        /* Snap all vertices */
        G_debug(3, "Snap all vertices");
        for (v = 0; v < Points->n_points; v++) {
            /* Box */
            c[0] = Points->x[v];
            c[1] = Points->y[v];

            /* Find point ( should always find one point ) */
            Vect_reset_list(List);

            spoint = -1;
            kdtree_knn(KDTree, c, &spoint, &kddist, 1, NULL);
            if (spoint == -1)
                G_fatal_error("Point not in KD Tree");

            anchor = XPnts[spoint].anchor;

            if (anchor > 0) {   /* to be snapped */
                Points->x[v] = XPnts[anchor].x;
                Points->y[v] = XPnts[anchor].y;
                nsnapped++;
                changed = 1;
                Index[v] = anchor;      /* point on new location */
            }
            else {
                Index[v] = spoint;      /* old point */
            }
        }

        /* New points */
        Vect_reset_line(NPoints);

        /* Snap all segments to anchors in threshold */
        G_debug(3, "Snap all segments");
        for (v = 0; v < Points->n_points - 1; v++) {
            int i;
            double x1, x2, y1, y2, xmin, xmax, ymin, ymax;
            double rc[4];

            G_debug(3, "  segment = %d end anchors : %d  %d", v, Index[v],
                    Index[v + 1]);

            x1 = Points->x[v];
            x2 = Points->x[v + 1];
            y1 = Points->y[v];
            y2 = Points->y[v + 1];

            Vect_append_point(NPoints, Points->x[v], Points->y[v],
                              Points->z[v]);

            /* Box */
            if (x1 <= x2) {
                xmin = x1;
                xmax = x2;
            }
            else {
                xmin = x2;
                xmax = x1;
            }
            if (y1 <= y2) {
                ymin = y1;
                ymax = y2;
            }
            else {
                ymin = y2;
                ymax = y1;
            }

            /* Find points */
            Vect_reset_list(List);
            G_debug(3, "  search anchors for segment %g,%g to %g,%g", x1, y1, x2, y2);
            /* distance search: circle around midpoint encompassing 
             *                  endpoints
             * box search: box encompassing endpoints, 
             *             smaller than corresponding circle */
            rc[0] = xmin - thresh * 2;
            rc[1] = ymin - thresh * 2;
            rc[2] = xmax + thresh * 2;
            rc[3] = ymax + thresh * 2;
            
            kd_found = kdtree_rnn(KDTree, rc, &kduid, NULL);

            G_debug(3, "  %d points in box", kd_found);

            /* Snap to anchor in threshold different from end points */
            nnew = 0;
            for (i = 0; i < kd_found; i++) {
                double dist2, along;
                int status;

                spoint = kduid[i];
                G_debug(4, "    spoint = %d anchor = %d", spoint,
                        XPnts[spoint].anchor);

                if (spoint == Index[v] || spoint == Index[v + 1])
                    continue;   /* end point */
                if (XPnts[spoint].anchor > 0)
                    continue;   /* point is not anchor */

                /* Check the distance */
                dist2 =
                    dig_distance2_point_to_line(XPnts[spoint].x,
                                                XPnts[spoint].y, 0, x1, y1, 0,
                                                x2, y2, 0, 0, NULL, NULL,
                                                NULL, &along, &status);

                G_debug(4, "      distance = %lf", sqrt(dist2));

                if (status == 0 && dist2 <= thresh2) {
                    G_debug(4, "      anchor in thresh, along = %lf", along);

                    if (nnew == anew) {
                        anew += 100;
                        New = (NEW *) G_realloc(New, anew * sizeof(NEW));
                    }
                    New[nnew].anchor = spoint;
                    New[nnew].along = along;
                    nnew++;
                }
            }
            if (kd_found) {
                G_free(kduid);
            }
            G_debug(3, "  nnew = %d", nnew);
            /* insert new vertices */
            if (nnew > 0) {
                /* sort by distance along the segment */
                qsort(New, sizeof(char) * nnew, sizeof(NEW), sort_new);

                for (i = 0; i < nnew; i++) {
                    anchor = New[i].anchor;
                    /* Vect_line_insert_point ( Points, ++v, XPnts[anchor].x, XPnts[anchor].y, 0); */
                    Vect_append_point(NPoints, XPnts[anchor].x,
                                      XPnts[anchor].y, 0);
                    ncreated++;
                }
                changed = 1;
            }
        }

        /* append end point */
        v = Points->n_points - 1;
        Vect_append_point(NPoints, Points->x[v], Points->y[v], Points->z[v]);

        if (changed) {          /* rewrite the line */
            Vect_line_prune(NPoints);   /* remove duplicates */
            if (NPoints->n_points > 1 || !(ltype & GV_LINES)) {
                Vect_rewrite_line(Map, line, ltype, NPoints, Cats);
            }
            else {
                Vect_delete_line(Map, line);
            }
            if (Err) {
                Vect_write_line(Err, ltype, Points, Cats);
            }
        }
    }                           /* for each line */
    G_percent(line_idx, List_lines->n_values, 2); /* finish it */

    Vect_destroy_line_struct(Points);
    Vect_destroy_line_struct(NPoints);
    Vect_destroy_cats_struct(Cats);
    G_free(XPnts);
    G_free(Index);
    G_free(New);
    kdtree_destroy(KDTree);

    G_verbose_message(_("Snapped vertices: %d"), nsnapped);
    G_verbose_message(_("New vertices: %d"), ncreated);
}

static void
Vect_snap_lines_list_rtree(struct Map_info *Map, const struct ilist *List_lines,
                     double thresh, struct Map_info *Err)
{
    struct line_pnts *Points, *NPoints;
    struct line_cats *Cats;
    int line, ltype, line_idx;
    double thresh2;

    int point;                  /* index in points array */
    int nanchors, ntosnap;      /* number of anchors and number of points to be snapped */
    int nsnapped, ncreated;     /* number of snapped verices, number of new vertices (on segments) */
    int apoints, npoints, nvertices;    /* number of allocated points, registered points, vertices */
    XPNT *XPnts;                /* Array of points */
    NEW *New = NULL;            /* Array of new points */
    int anew = 0, nnew;         /* allocated new points , number of new points */
    struct ilist *List;
    int *Index = NULL;          /* indexes of anchors for vertices */
    int aindex = 0;             /* allocated Index */

    struct RTree *RTree;
    int rtreefd = -1;
    static struct RTree_Rect rect;
    static int rect_init = 0;

    if (!rect_init) {
        rect.boundary = G_malloc(6 * sizeof(RectReal));
        rect_init = 6;
    }

    if (List_lines->n_values < 1)
        return;

    Points = Vect_new_line_struct();
    NPoints = Vect_new_line_struct();
    Cats = Vect_new_cats_struct();
    List = Vect_new_list();
    if (getenv("GRASS_VECTOR_LOWMEM")) {
        char *filename = G_tempfile();

        rtreefd = open(filename, O_RDWR | O_CREAT | O_EXCL, 0600);
        remove(filename);
    }
    RTree = RTreeCreateTree(rtreefd, 0, 2);

    thresh2 = thresh * thresh;

    /* Go through all lines in vector, and add each point to structure of points */
    apoints = 0;
    point = 1;                  /* index starts from 1 ! */
    nvertices = 0;
    XPnts = NULL;

    G_important_message(_("Snap vertices Pass 1: select points"));
    for (line_idx = 0; line_idx < List_lines->n_values; line_idx++) {
        int v;

        G_percent(line_idx, List_lines->n_values, 2);

        line = List_lines->value[line_idx];

        G_debug(3, "line =  %d", line);
        if (!Vect_line_alive(Map, line))
            continue;

        ltype = Vect_read_line(Map, Points, Cats, line);

        for (v = 0; v < Points->n_points; v++) {
            G_debug(3, "  vertex v = %d", v);
            nvertices++;

            /* Box */
            rect.boundary[0] = Points->x[v];
            rect.boundary[3] = Points->x[v];
            rect.boundary[1] = Points->y[v];
            rect.boundary[4] = Points->y[v];
            rect.boundary[2] = 0;
            rect.boundary[5] = 0;

            /* Already registered ? */
            Vect_reset_list(List);
            RTreeSearch(RTree, &rect, find_item, List);
            G_debug(3, "List : nvalues =  %d", List->n_values);

            if (List->n_values == 0) {  /* Not found */
                /* Add to tree and to structure */
                RTreeInsertRect(&rect, point, RTree);
                if ((point - 1) == apoints) {
                    apoints += 10000;
                    XPnts =
                        (XPNT *) G_realloc(XPnts,
                                           (apoints + 1) * sizeof(XPNT));
                }
                XPnts[point].x = Points->x[v];
                XPnts[point].y = Points->y[v];
                XPnts[point].anchor = -1;
                point++;
            }
        }
    }
    G_percent(line_idx, List_lines->n_values, 2); /* finish it */

    npoints = point - 1;

    /* Go through all registered points and if not yet marked mark it as anchor and assign this anchor
     * to all not yet marked points in threshold */

    G_important_message(_("Snap vertices Pass 2: assign anchor vertices"));

    nanchors = ntosnap = 0;
    for (point = 1; point <= npoints; point++) {
        int i;

        G_percent(point, npoints, 4);

        G_debug(3, "  point = %d", point);

        if (XPnts[point].anchor >= 0)
            continue;

        XPnts[point].anchor = 0;        /* make it anchor */
        nanchors++;

        /* Find points in threshold */
        rect.boundary[0] = XPnts[point].x - thresh;
        rect.boundary[3] = XPnts[point].x + thresh;
        rect.boundary[1] = XPnts[point].y - thresh;
        rect.boundary[4] = XPnts[point].y + thresh;
        rect.boundary[2] = 0;
        rect.boundary[5] = 0;

        Vect_reset_list(List);
        RTreeSearch(RTree, &rect, add_item, List);
        G_debug(4, "  %d points in threshold box", List->n_values);

        for (i = 0; i < List->n_values; i++) {
            int pointb;
            double dx, dy, dist2;

            pointb = List->value[i];
            if (pointb == point)
                continue;

            dx = XPnts[pointb].x - XPnts[point].x;
            dy = XPnts[pointb].y - XPnts[point].y;
            dist2 = dx * dx + dy * dy;

            if (dist2 > thresh2) /* outside threshold */
                continue;
                
            /* doesn't have an anchor yet */
            if (XPnts[pointb].anchor == -1) {
                XPnts[pointb].anchor = point;
                ntosnap++;
            }
            else if (XPnts[pointb].anchor > 0) {   /* check distance to previously assigned anchor */
                double dist2_a;

                dx = XPnts[XPnts[pointb].anchor].x - XPnts[pointb].x;
                dy = XPnts[XPnts[pointb].anchor].y - XPnts[pointb].y;
                dist2_a = dx * dx + dy * dy;

                /* replace old anchor */
                if (dist2 < dist2_a) {
                    XPnts[pointb].anchor = point;
                }
            }
        }
    }

    /* Go through all lines and: 
     *   1) for all vertices: if not anchor snap it to its anchor
     *   2) for all segments: snap it to all anchors in threshold (except anchors of vertices of course) */

    nsnapped = ncreated = 0;

    G_important_message(_("Snap vertices Pass 3: snap to assigned points"));

    for (line_idx = 0; line_idx < List_lines->n_values; line_idx++) {
        int v, spoint, anchor;
        int changed = 0;

        G_percent(line_idx, List_lines->n_values, 2);

        line = List_lines->value[line_idx];

        G_debug(3, "line =  %d", line);
        if (!Vect_line_alive(Map, line))
            continue;

        ltype = Vect_read_line(Map, Points, Cats, line);

        if (Points->n_points >= aindex) {
            aindex = Points->n_points;
            Index = (int *)G_realloc(Index, aindex * sizeof(int));
        }

        /* Snap all vertices */
        for (v = 0; v < Points->n_points; v++) {
            /* Box */
            rect.boundary[0] = Points->x[v];
            rect.boundary[3] = Points->x[v];
            rect.boundary[1] = Points->y[v];
            rect.boundary[4] = Points->y[v];
            rect.boundary[2] = 0;
            rect.boundary[5] = 0;

            /* Find point ( should always find one point ) */
            Vect_reset_list(List);

            RTreeSearch(RTree, &rect, add_item, List);

            spoint = List->value[0];
            anchor = XPnts[spoint].anchor;

            if (anchor > 0) {   /* to be snapped */
                Points->x[v] = XPnts[anchor].x;
                Points->y[v] = XPnts[anchor].y;
                nsnapped++;
                changed = 1;
                Index[v] = anchor;      /* point on new location */
            }
            else {
                Index[v] = spoint;      /* old point */
            }
        }

        /* New points */
        Vect_reset_line(NPoints);

        /* Snap all segments to anchors in threshold */
        for (v = 0; v < Points->n_points - 1; v++) {
            int i;
            double x1, x2, y1, y2, xmin, xmax, ymin, ymax;

            G_debug(3, "  segment = %d end anchors : %d  %d", v, Index[v],
                    Index[v + 1]);

            x1 = Points->x[v];
            x2 = Points->x[v + 1];
            y1 = Points->y[v];
            y2 = Points->y[v + 1];

            Vect_append_point(NPoints, Points->x[v], Points->y[v],
                              Points->z[v]);

            /* Box */
            if (x1 <= x2) {
                xmin = x1;
                xmax = x2;
            }
            else {
                xmin = x2;
                xmax = x1;
            }
            if (y1 <= y2) {
                ymin = y1;
                ymax = y2;
            }
            else {
                ymin = y2;
                ymax = y1;
            }

            rect.boundary[0] = xmin - thresh;
            rect.boundary[3] = xmax + thresh;
            rect.boundary[1] = ymin - thresh;
            rect.boundary[4] = ymax + thresh;
            rect.boundary[2] = 0;
            rect.boundary[5] = 0;

            /* Find points */
            Vect_reset_list(List);
            RTreeSearch(RTree, &rect, add_item, List);

            G_debug(3, "  %d points in box", List->n_values);

            /* Snap to anchor in threshold different from end points */
            nnew = 0;
            for (i = 0; i < List->n_values; i++) {
                double dist2, along;
                int status;

                spoint = List->value[i];
                G_debug(4, "    spoint = %d anchor = %d", spoint,
                        XPnts[spoint].anchor);

                if (spoint == Index[v] || spoint == Index[v + 1])
                    continue;   /* end point */
                if (XPnts[spoint].anchor > 0)
                    continue;   /* point is not anchor */

                /* Check the distance */
                dist2 =
                    dig_distance2_point_to_line(XPnts[spoint].x,
                                                XPnts[spoint].y, 0, x1, y1, 0,
                                                x2, y2, 0, 0, NULL, NULL,
                                                NULL, &along, &status);

                G_debug(4, "      distance = %lf", sqrt(dist2));

                if (status == 0 && dist2 <= thresh2) {
                    G_debug(4, "      anchor in thresh, along = %lf", along);

                    if (nnew == anew) {
                        anew += 100;
                        New = (NEW *) G_realloc(New, anew * sizeof(NEW));
                    }
                    New[nnew].anchor = spoint;
                    New[nnew].along = along;
                    nnew++;
                }
            }
            G_debug(3, "  nnew = %d", nnew);
            /* insert new vertices */
            if (nnew > 0) {
                /* sort by distance along the segment */
                qsort(New, sizeof(char) * nnew, sizeof(NEW), sort_new);

                for (i = 0; i < nnew; i++) {
                    anchor = New[i].anchor;
                    /* Vect_line_insert_point ( Points, ++v, XPnts[anchor].x, XPnts[anchor].y, 0); */
                    Vect_append_point(NPoints, XPnts[anchor].x,
                                      XPnts[anchor].y, 0);
                    ncreated++;
                }
                changed = 1;
            }
        }

        /* append end point */
        v = Points->n_points - 1;
        Vect_append_point(NPoints, Points->x[v], Points->y[v], Points->z[v]);

        if (changed) {          /* rewrite the line */
            Vect_line_prune(NPoints);   /* remove duplicates */
            if (NPoints->n_points > 1 || !(ltype & GV_LINES)) {
                Vect_rewrite_line(Map, line, ltype, NPoints, Cats);
            }
            else {
                Vect_delete_line(Map, line);
            }
            if (Err) {
                Vect_write_line(Err, ltype, Points, Cats);
            }
        }
    }                           /* for each line */
    G_percent(line_idx, List_lines->n_values, 2); /* finish it */

    Vect_destroy_line_struct(Points);
    Vect_destroy_line_struct(NPoints);
    Vect_destroy_cats_struct(Cats);
    G_free(XPnts);
    G_free(Index);
    G_free(New);
    RTreeDestroyTree(RTree);
    if (rtreefd >= 0)
        close(rtreefd);

    G_verbose_message(_("Snapped vertices: %d"), nsnapped);
    G_verbose_message(_("New vertices: %d"), ncreated);
}


/*!
   \brief Snap lines in vector map to existing vertex in threshold.
  
   For details see Vect_snap_lines_list()
  
   \param[in] Map input map where vertices will be snapped
   \param[in] type type of lines to snap
   \param[in] thresh threshold in which snap vertices
   \param[out] Err vector map where lines representing snap are written or NULL
  
   \return void
 */
void
Vect_snap_lines(struct Map_info *Map, int type, double thresh,
                struct Map_info *Err)
{
    int line, nlines, ltype;
    struct ilist *List;

    List = Vect_new_list();

    nlines = Vect_get_num_lines(Map);

    G_important_message(_("Reading features..."));
    for (line = 1; line <= nlines; line++) {
        G_debug(3, "line =  %d", line);

        if (!Vect_line_alive(Map, line))
            continue;

        ltype = Vect_read_line(Map, NULL, NULL, line);

        if (!(ltype & type))
            continue;

        G_ilist_add(List, line);
    }

    Vect_snap_lines_list(Map, List, thresh, Err);

    Vect_destroy_list(List);

    return;
}

/*!
   \brief Snap a line to reference lines in Map with threshold.
  
   3D snapping is supported. The line to snap and the reference lines 
   can but do not need to be in different vector maps.
   
   Vect_snap_line() uses less memory, but is slower than 
   Vect_snap_lines_list()

   For details on snapping, see Vect_snap_lines_list()

   \param[in] Map input map with reference lines
   \param[in] reflist list of reference lines
   \param[in,out] Points line points to snap
   \param[in] thresh threshold in which to snap vertices
   \param[in] with_z 2D or 3D snapping
   \param[in,out] nsnapped number of snapped vertices
   \param[in,out] ncreated number of new vertices (on segments)
  
   \return 1 if line was changed, otherwise 0
 */
int
Vect_snap_line(struct Map_info *Map, struct ilist *reflist,
               struct line_pnts *Points, double thresh, int with_z,
               int *nsnapped, int *ncreated)
{
    struct line_pnts *LPoints, *NPoints;
    struct line_cats *Cats;
    int i, v, line, nlines;
    int changed;
    double thresh2;

    int point;                  /* index in points array */
    int segment;                /* index in segments array */
    int asegments;              /* number of allocated segments */
    int nvertices;              /* number of vertices */
    char *XSegs = NULL;         /* Array of segments */
    NEW2 *New = NULL;           /* Array of new points */
    int anew = 0, nnew;         /* allocated new points , number of new points */
    struct boxlist *List;

    struct RTree *pnt_tree,     /* spatial index for reference points */
                 *seg_tree;     /* spatial index for reference segments */
    struct RTree_Rect rect;

    rect.boundary = G_malloc(6 * sizeof(RectReal));
    rect.boundary[0] = 0;
    rect.boundary[1] = 0;
    rect.boundary[2] = 0;
    rect.boundary[3] = 0;
    rect.boundary[4] = 0;
    rect.boundary[5] = 0;

    changed = 0;
    if (nsnapped)
        *nsnapped = 0;
    if (ncreated)
        *ncreated = 0;

    point = Points->n_points;
    Vect_line_prune(Points);
    if (point != Points->n_points)
        changed = 1;

    nlines = reflist->n_values;
    if (nlines < 1)
        return changed;

    LPoints = Vect_new_line_struct();
    NPoints = Vect_new_line_struct();
    Cats = Vect_new_cats_struct();
    List = Vect_new_boxlist(1);
    with_z = (with_z != 0);
    pnt_tree = RTreeCreateTree(-1, 0, 2 + with_z);
    RTreeSetOverflow(pnt_tree, 0);
    seg_tree = RTreeCreateTree(-1, 0, 2 + with_z);
    RTreeSetOverflow(seg_tree, 0);

    thresh2 = thresh * thresh;

    point = segment = 1;        /* index starts from 1 ! */
    nvertices = 0;
    asegments = 0;

    /* Add all vertices and all segments of all reference lines 
     * to spatial indices */
    nlines = reflist->n_values;
    for (i = 0; i < nlines; i++) {

        line = reflist->value[i];

        G_debug(3, "line =  %d", line);
        if (!Vect_line_alive(Map, line))
            continue;

        Vect_read_line(Map, LPoints, Cats, line);
        Vect_line_prune(LPoints);

        for (v = 0; v < LPoints->n_points; v++) {
            G_debug(3, "  vertex v = %d", v);
            nvertices++;

            /* Box */
            rect.boundary[0] = LPoints->x[v];
            rect.boundary[3] = LPoints->x[v];
            rect.boundary[1] = LPoints->y[v];
            rect.boundary[4] = LPoints->y[v];
            if (with_z) {
                rect.boundary[2] = LPoints->z[v];
                rect.boundary[5] = LPoints->z[v];
            }

            /* Already registered ? */
            Vect_reset_boxlist(List);
            RTreeSearch(pnt_tree, &rect, find_item_box, (void *)List);
            G_debug(3, "List : nvalues =  %d", List->n_values);

            if (List->n_values == 0) {  /* Not found */

                /* Add to points tree */
                RTreeInsertRect(&rect, point, pnt_tree);

                point++;
            }
            
            /* reference segments */
            if (v) {
                char sides = 0;

                /* Box */
                if (LPoints->x[v - 1] < LPoints->x[v]) {
                    rect.boundary[0] = LPoints->x[v - 1];
                    rect.boundary[3] = LPoints->x[v];
                    sides |= X1W;
                }
                else {
                    rect.boundary[0] = LPoints->x[v];
                    rect.boundary[3] = LPoints->x[v - 1];
                }
                if (LPoints->y[v - 1] < LPoints->y[v]) {
                    rect.boundary[1] = LPoints->y[v - 1];
                    rect.boundary[4] = LPoints->y[v];
                    sides |= Y1S;
                }
                else {
                    rect.boundary[1] = LPoints->y[v];
                    rect.boundary[4] = LPoints->y[v - 1];
                }
                if (LPoints->z[v - 1] < LPoints->z[v]) {
                    rect.boundary[2] = LPoints->z[v - 1];
                    rect.boundary[5] = LPoints->z[v];
                    sides |= Z1B;
                }
                else {
                    rect.boundary[2] = LPoints->z[v];
                    rect.boundary[5] = LPoints->z[v - 1];
                }

                /* do not check for duplicates, too costly
                 * because different segments can have identical boxes */
                RTreeInsertRect(&rect, segment, seg_tree);

                if ((segment - 1) == asegments) {
                    asegments += 1000;
                    XSegs =
                        (char *) G_realloc(XSegs,
                                           (asegments + 1) * sizeof(char));
                }
                XSegs[segment] = sides;
                segment++;
            }
        }
    }

    /* go through all vertices of the line to snap */
    /* find nearest reference vertex */
    for (v = 0; v < Points->n_points; v++) {
        double dist2, tmpdist2;
        double x, y, z;

        dist2 = thresh2 + thresh2;
        x = Points->x[v];
        y = Points->y[v];
        z = Points->z[v];

        /* Box */
        rect.boundary[0] = Points->x[v] - thresh;
        rect.boundary[3] = Points->x[v] + thresh;
        rect.boundary[1] = Points->y[v] - thresh;
        rect.boundary[4] = Points->y[v] + thresh;
        if (with_z) {
            rect.boundary[2] = Points->z[v] - thresh;
            rect.boundary[5] = Points->z[v] + thresh;
        }

        Vect_reset_boxlist(List);

        RTreeSearch(pnt_tree, &rect, add_item_box, (void *)List);

        for (i = 0; i < List->n_values; i++) {
            double dx = List->box[i].E - Points->x[v];
            double dy = List->box[i].N - Points->y[v];
            double dz = 0;
            
            if (with_z)
                dz = List->box[i].T - Points->z[v];
            
            tmpdist2 = dx * dx + dy * dy + dz * dz;
            
            if (tmpdist2 < dist2) {
                dist2 = tmpdist2;

                x = List->box[i].E;
                y = List->box[i].N;
                z = List->box[i].T;
            }
        }

        if (dist2 <= thresh2 && dist2 > 0) {
            Points->x[v] = x;
            Points->y[v] = y;
            Points->z[v] = z;

            changed = 1;
            if (nsnapped)
                (*nsnapped)++;
        }
    }

    /* go through all vertices of the line to snap */
    /* find nearest reference segment */
    for (v = 0; v < Points->n_points; v++) {
        double dist2, tmpdist2;
        double x, y, z;
        
        dist2 = thresh2 + thresh2;
        x = Points->x[v];
        y = Points->y[v];
        z = Points->z[v];

        /* Box */
        rect.boundary[0] = Points->x[v] - thresh;
        rect.boundary[3] = Points->x[v] + thresh;
        rect.boundary[1] = Points->y[v] - thresh;
        rect.boundary[4] = Points->y[v] + thresh;
        if (with_z) {
            rect.boundary[2] = Points->z[v] - thresh;
            rect.boundary[5] = Points->z[v] + thresh;
        }

        Vect_reset_boxlist(List);

        RTreeSearch(seg_tree, &rect, add_item_box, (void *)List);

        for (i = 0; i < List->n_values; i++) {
            double x1, y1, z1, x2, y2, z2;
            double tmpx, tmpy, tmpz;
            int status;
            
            segment = List->id[i];

            if (XSegs[segment] & X1W) {
                x1 = List->box[i].W;
                x2 = List->box[i].E;
            }
            else {
                x1 = List->box[i].E;
                x2 = List->box[i].W;
            }
            if (XSegs[segment] & Y1S) {
                y1 = List->box[i].S;
                y2 = List->box[i].N;
            }
            else {
                y1 = List->box[i].N;
                y2 = List->box[i].S;
            }
            if (XSegs[segment] & Z1B) {
                z1 = List->box[i].B;
                z2 = List->box[i].T;
            }
            else {
                z1 = List->box[i].T;
                z2 = List->box[i].B;
            }

            /* Check the distance */
            tmpdist2 =
                dig_distance2_point_to_line(Points->x[v],
                                            Points->y[v],
                                            Points->z[v], 
                                            x1, y1, z1, x2, y2, z2,
                                            with_z, &tmpx, &tmpy, &tmpz,
                                            NULL, &status);

            if (tmpdist2 < dist2 && status == 0) {
                dist2 = tmpdist2;

                x = tmpx;
                y = tmpy;
                z = tmpz;
            }
        }

        if (dist2 <= thresh2 && dist2 > 0) {
            Points->x[v] = x;
            Points->y[v] = y;
            Points->z[v] = z;
            
            changed = 1;
            if (nsnapped)
                (*nsnapped)++;
        }
    }

    RTreeDestroyTree(seg_tree);
    G_free(XSegs);

    /* go through all segments of the line to snap */
    /* find nearest reference vertex, add this vertex */
    for (v = 0; v < Points->n_points - 1; v++) {
        double x1, x2, y1, y2, z1, z2;
        double xmin, xmax, ymin, ymax, zmin, zmax;

        x1 = Points->x[v];
        x2 = Points->x[v + 1];
        y1 = Points->y[v];
        y2 = Points->y[v + 1];
        if (with_z) {
            z1 = Points->z[v];
            z2 = Points->z[v + 1];
        }
        else {
            z1 = z2 = 0;
        }

        Vect_append_point(NPoints, Points->x[v], Points->y[v],
                          Points->z[v]);

        /* Box */
        if (x1 <= x2) {
            xmin = x1;
            xmax = x2;
        }
        else {
            xmin = x2;
            xmax = x1;
        }
        if (y1 <= y2) {
            ymin = y1;
            ymax = y2;
        }
        else {
            ymin = y2;
            ymax = y1;
        }
        if (z1 <= z2) {
            zmin = z1;
            zmax = z2;
        }
        else {
            zmin = z2;
            zmax = z1;
        }

        rect.boundary[0] = xmin - thresh;
        rect.boundary[3] = xmax + thresh;
        rect.boundary[1] = ymin - thresh;
        rect.boundary[4] = ymax + thresh;
        rect.boundary[2] = zmin - thresh;
        rect.boundary[5] = zmax + thresh;

        /* Find points */
        Vect_reset_boxlist(List);
        RTreeSearch(pnt_tree, &rect, add_item_box, (void *)List);

        G_debug(3, "  %d points in box", List->n_values);

        /* Snap to vertex in threshold different from end points */
        nnew = 0;
        for (i = 0; i < List->n_values; i++) {
            double dist2, along;
            int status;
            
            if (!with_z)
                List->box[i].T = 0;

            if (Points->x[v] == List->box[i].E && 
                Points->y[v] == List->box[i].N &&
                Points->z[v] == List->box[i].T)
                continue;       /* start point */

            if (Points->x[v + 1] == List->box[i].E && 
                Points->y[v + 1] == List->box[i].N &&
                Points->z[v + 1] == List->box[i].T)
                continue;       /* end point */

            /* Check the distance */
            dist2 =
                dig_distance2_point_to_line(List->box[i].E,
                                            List->box[i].N,
                                            List->box[i].T, x1, y1, z1,
                                            x2, y2, z2, with_z, NULL, NULL,
                                            NULL, &along, &status);

            if (dist2 <= thresh2 && status == 0) {
                G_debug(4, "      anchor in thresh, along = %lf", along);

                if (nnew == anew) {
                    anew += 100;
                    New = (NEW2 *) G_realloc(New, anew * sizeof(NEW2));
                }
                New[nnew].x = List->box[i].E;
                New[nnew].y = List->box[i].N;
                New[nnew].z = List->box[i].T;
                New[nnew].along = along;
                nnew++;
            }
            G_debug(3, "dist: %g, thresh: %g", dist2, thresh2);
        }
        G_debug(3, "  nnew = %d", nnew);
        /* insert new vertices */
        if (nnew > 0) {
            /* sort by distance along the segment */
            qsort(New, nnew, sizeof(NEW2), sort_new2);

            for (i = 0; i < nnew; i++) {
                Vect_append_point(NPoints, New[i].x, New[i].y, New[i].z);
                if (ncreated)
                    (*ncreated)++;
            }
            changed = 1;
        }
    }

    /* append end point */
    v = Points->n_points - 1;
    Vect_append_point(NPoints, Points->x[v], Points->y[v], Points->z[v]);

    if (Points->n_points != NPoints->n_points) {
        Vect_line_prune(NPoints);       /* remove duplicates */
        Vect_reset_line(Points);
        Vect_append_points(Points, NPoints, GV_FORWARD);
    }

    Vect_destroy_line_struct(LPoints);
    Vect_destroy_line_struct(NPoints);
    Vect_destroy_cats_struct(Cats);
    Vect_destroy_boxlist(List);
    G_free(New);
    RTreeDestroyTree(pnt_tree);
    G_free(rect.boundary);

    return changed;
}