postgis/liblwgeom/lwsegmentize.c

/**********************************************************************
 * $Id$
 *
 * PostGIS - Spatial Types for PostgreSQL
 * http://postgis.refractions.net
 * Copyright 2001-2006 Refractions Research Inc.
 *
 * This is free software; you can redistribute and/or modify it under
 * the terms of the GNU General Public Licence. See the COPYING file.
 *
 **********************************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>

#include "liblwgeom_internal.h"
#include "lwgeom_log.h"


LWMLINE *lwmcurve_segmentize(LWMCURVE *mcurve, uint32_t perQuad);
LWMPOLY *lwmsurface_segmentize(LWMSURFACE *msurface, uint32_t perQuad);
LWCOLLECTION *lwcollection_segmentize(LWCOLLECTION *collection, uint32_t perQuad);

LWGEOM *pta_desegmentize(POINTARRAY *points, int type, int srid);
LWGEOM *lwline_desegmentize(LWLINE *line);
LWGEOM *lwpolygon_desegmentize(LWPOLY *poly);
LWGEOM *lwmline_desegmentize(LWMLINE *mline);
LWGEOM *lwmpolygon_desegmentize(LWMPOLY *mpoly);
LWGEOM *lwgeom_desegmentize(LWGEOM *geom);


/*
 * Tolerance used to determine equality.
 */
#define EPSILON_SQLMM 1e-8

/*
 * Determines (recursively in the case of collections) whether the geometry
 * contains at least on arc geometry or segment.
 */
int
lwgeom_has_arc(const LWGEOM *geom)
{
	LWCOLLECTION *col;
	int i;

	LWDEBUG(2, "lwgeom_has_arc called.");

	switch (geom->type)
	{
	case POINTTYPE:
	case LINETYPE:
	case POLYGONTYPE:
	case TRIANGLETYPE:
	case MULTIPOINTTYPE:
	case MULTILINETYPE:
	case MULTIPOLYGONTYPE:
	case POLYHEDRALSURFACETYPE:
	case TINTYPE:
		return LW_FALSE;
	case CIRCSTRINGTYPE:
		return LW_TRUE;
	/* It's a collection that MAY contain an arc */
	default:
		col = (LWCOLLECTION *)geom;
		for (i=0; i<col->ngeoms; i++)
		{
			if (lwgeom_has_arc(col->geoms[i]) == LW_TRUE) 
				return LW_TRUE;
		}
		return LW_FALSE;
	}
}

/*
 * Determines the center of the circle defined by the three given points.
 * In the event the circle is complete, the midpoint of the segment defined
 * by the first and second points is returned.  If the points are colinear,
 * as determined by equal slopes, then NULL is returned.  If the interior
 * point is coincident with either end point, they are taken as colinear.
 */
double
lwcircle_center(const POINT4D *p1, const POINT4D *p2, const POINT4D *p3, POINT4D *result)
{
	POINT4D c;
	double cx, cy, cr;
	double temp, bc, cd, det;

    c.x = c.y = c.z = c.m = 0.0;

	LWDEBUGF(2, "lwcircle_center called (%.16f,%.16f), (%.16f,%.16f), (%.16f,%.16f).", p1->x, p1->y, p2->x, p2->y, p3->x, p3->y);

	/* Closed circle */
	if (fabs(p1->x - p3->x) < EPSILON_SQLMM &&
	    fabs(p1->y - p3->y) < EPSILON_SQLMM)
	{
		cx = p1->x + (p2->x - p1->x) / 2.0;
		cy = p1->y + (p2->y - p1->y) / 2.0;
		c.x = cx;
		c.y = cy;
		*result = c;
		cr = sqrt(pow(cx - p1->x, 2.0) + pow(cy - p1->y, 2.0));
		return cr;
	}

	temp = p2->x*p2->x + p2->y*p2->y;
	bc = (p1->x*p1->x + p1->y*p1->y - temp) / 2.0;
	cd = (temp - p3->x*p3->x - p3->y*p3->y) / 2.0;
	det = (p1->x - p2->x)*(p2->y - p3->y)-(p2->x - p3->x)*(p1->y - p2->y);

	/* Check colinearity */
	if (fabs(det) < EPSILON_SQLMM)
		return -1.0;


	det = 1.0 / det;
	cx = (bc*(p2->y - p3->y)-cd*(p1->y - p2->y))*det;
	cy = ((p1->x - p2->x)*cd-(p2->x - p3->x)*bc)*det;
	c.x = cx;
	c.y = cy;
	*result = c;
	cr = sqrt((cx-p1->x)*(cx-p1->x)+(cy-p1->y)*(cy-p1->y));
	
	LWDEBUGF(2, "lwcircle_center center is (%.16f,%.16f)", result->x, result->y);
	
	return cr;
}


/*******************************************************************************
 * Begin curve segmentize functions
 ******************************************************************************/

static double interpolate_arc(double angle, double a1, double a2, double a3, double zm1, double zm2, double zm3)
{
	LWDEBUGF(4,"angle %.05g a1 %.05g a2 %.05g a3 %.05g zm1 %.05g zm2 %.05g zm3 %.05g",angle,a1,a2,a3,zm1,zm2,zm3);
	/* Counter-clockwise sweep */
	if ( a1 < a2 )
	{
		if ( angle <= a2 )
			return zm1 + (zm2-zm1) * (angle-a1) / (a2-a1);
		else
			return zm2 + (zm3-zm2) * (angle-a2) / (a3-a2);
	}
	/* Clockwise sweep */
	else
	{
		if ( angle >= a2 )
			return zm1 + (zm2-zm1) * (a1-angle) / (a1-a2);
		else
			return zm2 + (zm3-zm2) * (a2-angle) / (a2-a3);
	}
}

static POINTARRAY *
lwcircle_segmentize(POINT4D *p1, POINT4D *p2, POINT4D *p3, uint32_t perQuad)
{
	POINT4D center;
	POINT4D pt;
	int p2_side = 0;
	int clockwise = LW_TRUE;
	double radius; /* Arc radius */
	double increment; /* Angle per segment */
	double a1, a2, a3, angle;
	POINTARRAY *pa;
	int result;
	int is_circle = LW_FALSE;

	LWDEBUG(2, "lwcircle_calculate_gbox called.");

	radius = lwcircle_center(p1, p2, p3, &center);
	p2_side = signum(lw_segment_side((POINT2D*)p1, (POINT2D*)p3, (POINT2D*)p2));

	/* Matched start/end points imply circle */
	if ( p1->x == p3->x && p1->y == p3->y )
		is_circle = LW_TRUE;
	
	/* Negative radius signals straight line, p1/p2/p3 are colinear */
	if ( radius < 0.0 || p2_side == 0 )
	    return NULL;
		
	/* The side of the p1/p3 line that p2 falls on dictates the sweep  
	   direction from p1 to p3. */
	if ( p2_side == -1 )
		clockwise = LW_TRUE;
	else
		clockwise = LW_FALSE;
		
	increment = fabs(M_PI_2 / perQuad);
	
	/* Angles of each point that defines the arc section */
	a1 = atan2(p1->y - center.y, p1->x - center.x);
	a2 = atan2(p2->y - center.y, p2->x - center.x);
	a3 = atan2(p3->y - center.y, p3->x - center.x);

	/* p2 on left side => clockwise sweep */
	if ( clockwise )
	{
		increment *= -1;
		/* Adjust a3 down so we can decrement from a1 to a3 cleanly */
		if ( a3 > a1 )
			a3 -= 2.0 * M_PI;
		if ( a2 > a1 )
			a2 -= 2.0 * M_PI;
	}
	/* p2 on right side => counter-clockwise sweep */
	else
	{
		/* Adjust a3 up so we can increment from a1 to a3 cleanly */
		if ( a3 < a1 )
			a3 += 2.0 * M_PI;
		if ( a2 < a1 )
			a2 += 2.0 * M_PI;
	}
	
	/* Override angles for circle case */
	if( is_circle )
	{
		a3 = a1 + 2.0 * M_PI;
		a2 = a1 + M_PI;
		increment = fabs(increment);
		clockwise = LW_FALSE;
	}
	
	/* Initialize point array */
	pa = ptarray_construct_empty(1, 1, 32);

	/* Sweep from a1 to a3 */
	for ( angle = a1; clockwise ? angle > a3 : angle < a3; angle += increment ) 
	{
		pt.x = center.x + radius * cos(angle);
		pt.y = center.y + radius * sin(angle);
		pt.z = interpolate_arc(angle, a1, a2, a3, p1->z, p2->z, p3->z);
		pt.m = interpolate_arc(angle, a1, a2, a3, p1->m, p2->m, p3->m);
		result = ptarray_append_point(pa, &pt, LW_FALSE);
	}	
	return pa;
}

LWLINE *
lwcircstring_segmentize(const LWCIRCSTRING *icurve, uint32_t perQuad)
{
	LWLINE *oline;
	POINTARRAY *ptarray;
	POINTARRAY *tmp;
	uint32_t i, j;
	POINT4D p1, p2, p3, p4;

	LWDEBUGF(2, "lwcircstring_segmentize called., dim = %d", icurve->points->flags);

	ptarray = ptarray_construct_empty(FLAGS_GET_Z(icurve->points->flags), FLAGS_GET_M(icurve->points->flags), 64);

	for (i = 2; i < icurve->points->npoints; i+=2)
	{
		LWDEBUGF(3, "lwcircstring_segmentize: arc ending at point %d", i);

		getPoint4d_p(icurve->points, i - 2, &p1);
		getPoint4d_p(icurve->points, i - 1, &p2);
		getPoint4d_p(icurve->points, i, &p3);
		tmp = lwcircle_segmentize(&p1, &p2, &p3, perQuad);

		if (tmp)
		{
			LWDEBUGF(3, "lwcircstring_segmentize: generated %d points", tmp->npoints);

			for (j = 0; j < tmp->npoints; j++)
			{
				getPoint4d_p(tmp, j, &p4);
				ptarray_append_point(ptarray, &p4, LW_TRUE);
			}
			ptarray_free(tmp);
		}
		else
		{
			LWDEBUG(3, "lwcircstring_segmentize: points are colinear, returning curve points as line");

			for (j = i - 1 ; j <= i ; j++)
			{
				getPoint4d_p(icurve->points, j, &p4);
				ptarray_append_point(ptarray, &p4, LW_TRUE);
			}
		}

	}
	getPoint4d_p(icurve->points, icurve->points->npoints-1, &p1);
	ptarray_append_point(ptarray, &p1, LW_TRUE);
		
	oline = lwline_construct(icurve->srid, NULL, ptarray);
	return oline;
}

LWLINE *
lwcompound_segmentize(const LWCOMPOUND *icompound, uint32_t perQuad)
{
	LWGEOM *geom;
	POINTARRAY *ptarray = NULL, *ptarray_out = NULL;
	LWLINE *tmp = NULL;
	uint32_t i, j;
	POINT4D p;

	LWDEBUG(2, "lwcompound_segmentize called.");

	ptarray = ptarray_construct_empty(FLAGS_GET_Z(icompound->flags), FLAGS_GET_M(icompound->flags), 64);

	for (i = 0; i < icompound->ngeoms; i++)
	{
		geom = icompound->geoms[i];
		if (geom->type == CIRCSTRINGTYPE)
		{
			tmp = lwcircstring_segmentize((LWCIRCSTRING *)geom, perQuad);
			for (j = 0; j < tmp->points->npoints; j++)
			{
				getPoint4d_p(tmp->points, j, &p);
				ptarray_append_point(ptarray, &p, LW_TRUE);
			}
			lwfree(tmp);
		}
		else if (geom->type == LINETYPE)
		{
			tmp = (LWLINE *)geom;
			for (j = 0; j < tmp->points->npoints; j++)
			{
				getPoint4d_p(tmp->points, j, &p);
				ptarray_append_point(ptarray, &p, LW_TRUE);
			}
		}
		else
		{
			lwerror("Unsupported geometry type %d found.",
			        geom->type, lwtype_name(geom->type));
			return NULL;
		}
	}
	ptarray_out = ptarray_remove_repeated_points(ptarray);
	ptarray_free(ptarray);
	return lwline_construct(icompound->srid, NULL, ptarray_out);
}

LWPOLY *
lwcurvepoly_segmentize(const LWCURVEPOLY *curvepoly, uint32_t perQuad)
{
	LWPOLY *ogeom;
	LWGEOM *tmp;
	LWLINE *line;
	POINTARRAY **ptarray;
	int i;

	LWDEBUG(2, "lwcurvepoly_segmentize called.");

	ptarray = lwalloc(sizeof(POINTARRAY *)*curvepoly->nrings);

	for (i = 0; i < curvepoly->nrings; i++)
	{
		tmp = curvepoly->rings[i];
		if (tmp->type == CIRCSTRINGTYPE)
		{
			line = lwcircstring_segmentize((LWCIRCSTRING *)tmp, perQuad);
			ptarray[i] = ptarray_clone_deep(line->points);
			lwfree(line);
		}
		else if (tmp->type == LINETYPE)
		{
			line = (LWLINE *)tmp;
			ptarray[i] = ptarray_clone_deep(line->points);
		}
		else if (tmp->type == COMPOUNDTYPE)
		{
			line = lwcompound_segmentize((LWCOMPOUND *)tmp, perQuad);
			ptarray[i] = ptarray_clone_deep(line->points);
			lwfree(line);
		}
		else
		{
			lwerror("Invalid ring type found in CurvePoly.");
			return NULL;
		}
	}

	ogeom = lwpoly_construct(curvepoly->srid, NULL, curvepoly->nrings, ptarray);
	return ogeom;
}

LWMLINE *
lwmcurve_segmentize(LWMCURVE *mcurve, uint32_t perQuad)
{
	LWMLINE *ogeom;
	LWGEOM *tmp;
	LWGEOM **lines;
	int i;

	LWDEBUGF(2, "lwmcurve_segmentize called, geoms=%d, dim=%d.", mcurve->ngeoms, FLAGS_NDIMS(mcurve->flags));

	lines = lwalloc(sizeof(LWGEOM *)*mcurve->ngeoms);

	for (i = 0; i < mcurve->ngeoms; i++)
	{
		tmp = mcurve->geoms[i];
		if (tmp->type == CIRCSTRINGTYPE)
		{
			lines[i] = (LWGEOM *)lwcircstring_segmentize((LWCIRCSTRING *)tmp, perQuad);
		}
		else if (tmp->type == LINETYPE)
		{
			lines[i] = (LWGEOM *)lwline_construct(mcurve->srid, NULL, ptarray_clone_deep(((LWLINE *)tmp)->points));
		}
		else
		{
			lwerror("Unsupported geometry found in MultiCurve.");
			return NULL;
		}
	}

	ogeom = (LWMLINE *)lwcollection_construct(MULTILINETYPE, mcurve->srid, NULL, mcurve->ngeoms, lines);
	return ogeom;
}

LWMPOLY *
lwmsurface_segmentize(LWMSURFACE *msurface, uint32_t perQuad)
{
	LWMPOLY *ogeom;
	LWGEOM *tmp;
	LWPOLY *poly;
	LWGEOM **polys;
	POINTARRAY **ptarray;
	int i, j;

	LWDEBUG(2, "lwmsurface_segmentize called.");

	polys = lwalloc(sizeof(LWGEOM *)*msurface->ngeoms);

	for (i = 0; i < msurface->ngeoms; i++)
	{
		tmp = msurface->geoms[i];
		if (tmp->type == CURVEPOLYTYPE)
		{
			polys[i] = (LWGEOM *)lwcurvepoly_segmentize((LWCURVEPOLY *)tmp, perQuad);
		}
		else if (tmp->type == POLYGONTYPE)
		{
			poly = (LWPOLY *)tmp;
			ptarray = lwalloc(sizeof(POINTARRAY *)*poly->nrings);
			for (j = 0; j < poly->nrings; j++)
			{
				ptarray[j] = ptarray_clone_deep(poly->rings[j]);
			}
			polys[i] = (LWGEOM *)lwpoly_construct(msurface->srid, NULL, poly->nrings, ptarray);
		}
	}
	ogeom = (LWMPOLY *)lwcollection_construct(MULTIPOLYGONTYPE, msurface->srid, NULL, msurface->ngeoms, polys);
	return ogeom;
}

LWCOLLECTION *
lwcollection_segmentize(LWCOLLECTION *collection, uint32_t perQuad)
{
	LWCOLLECTION *ocol;
	LWGEOM *tmp;
	LWGEOM **geoms;
	int i;

	LWDEBUG(2, "lwcollection_segmentize called.");

	geoms = lwalloc(sizeof(LWGEOM *)*collection->ngeoms);

	for (i=0; i<collection->ngeoms; i++)
	{
		tmp = collection->geoms[i];
		switch (tmp->type)
		{
		case CIRCSTRINGTYPE:
			geoms[i] = (LWGEOM *)lwcircstring_segmentize((LWCIRCSTRING *)tmp, perQuad);
			break;
		case COMPOUNDTYPE:
			geoms[i] = (LWGEOM *)lwcompound_segmentize((LWCOMPOUND *)tmp, perQuad);
			break;
		case CURVEPOLYTYPE:
			geoms[i] = (LWGEOM *)lwcurvepoly_segmentize((LWCURVEPOLY *)tmp, perQuad);
			break;
		case COLLECTIONTYPE:
			geoms[i] = (LWGEOM *)lwcollection_segmentize((LWCOLLECTION *)tmp, perQuad);
			break;
		default:
			geoms[i] = lwgeom_clone(tmp);
			break;
		}
	}
	ocol = lwcollection_construct(COLLECTIONTYPE, collection->srid, NULL, collection->ngeoms, geoms);
	return ocol;
}

LWGEOM *
lwgeom_segmentize(LWGEOM *geom, uint32_t perQuad)
{
	LWGEOM * ogeom = NULL;
	switch (geom->type)
	{
	case CIRCSTRINGTYPE:
		ogeom = (LWGEOM *)lwcircstring_segmentize((LWCIRCSTRING *)geom, perQuad);
		break;
	case COMPOUNDTYPE:
		ogeom = (LWGEOM *)lwcompound_segmentize((LWCOMPOUND *)geom, perQuad);
		break;
	case CURVEPOLYTYPE:
		ogeom = (LWGEOM *)lwcurvepoly_segmentize((LWCURVEPOLY *)geom, perQuad);
		break;
	case MULTICURVETYPE:
		ogeom = (LWGEOM *)lwmcurve_segmentize((LWMCURVE *)geom, perQuad);
		break;
	case MULTISURFACETYPE:
		ogeom = (LWGEOM *)lwmsurface_segmentize((LWMSURFACE *)geom, perQuad);
		break;
	case COLLECTIONTYPE:
		ogeom = (LWGEOM *)lwcollection_segmentize((LWCOLLECTION *)geom, perQuad);
		break;
	default:
		ogeom = lwgeom_clone(geom);
	}
	return ogeom;
}


/**
* Returns LW_TRUE if b is on the arc formed by a1/a2/a3, but not within
* that portion already described by a1/a2/a3
*/
static int pt_continues_arc(const POINT4D *a1, const POINT4D *a2, const POINT4D *a3, const POINT4D *b)
{
	POINT4D center;
	POINT4D *centerptr=&center;
	double radius = lwcircle_center(a1, a2, a3, &center);
	double b_distance, diff;

	/* Co-linear a1/a2/a3 */
	if ( radius < 0.0 )
		return LW_FALSE;

	b_distance = distance2d_pt_pt((POINT2D*)b, (POINT2D*)centerptr);
	diff = fabs(radius - b_distance);
	LWDEBUGF(4, "circle_radius=%g, b_distance=%g, diff=%g, percentage=%g", radius, b_distance, diff, diff/radius);
	
	/* Is the point b on the circle? */
	if ( diff < EPSILON_SQLMM ) 
	{
		int a2_side = signum(lw_segment_side((POINT2D*)a1, (POINT2D*)a3, (POINT2D*)a2));
		int b_side = signum(lw_segment_side((POINT2D*)a1, (POINT2D*)a3, (POINT2D*)b));
		
		/* Is the point b on the same side of a1/a3 as the mid-point a2 is? */
		/* If not, it's in the unbounded part of the circle, so it continues the arc, return true. */
		if ( b_side != a2_side )
			return LW_TRUE;
	}
	return LW_FALSE;
}

static LWGEOM*
linestring_from_pa(const POINTARRAY *pa, int srid, int start, int end)
{
	int i = 0, j = 0;
	POINT4D p;
	POINTARRAY *pao = ptarray_construct(ptarray_has_z(pa), ptarray_has_m(pa), end-start+2);
	LWDEBUGF(4, "srid=%d, start=%d, end=%d", srid, start, end);
	for( i = start; i < end + 2; i++ )
	{
		getPoint4d_p(pa, i, &p);
		ptarray_set_point4d(pao, j++, &p);	
	}
	return lwline_as_lwgeom(lwline_construct(srid, NULL, pao));
}

static LWGEOM*
circstring_from_pa(const POINTARRAY *pa, int srid, int start, int end)
{
	
	POINT4D p0, p1, p2;
	POINTARRAY *pao = ptarray_construct(ptarray_has_z(pa), ptarray_has_m(pa), 3);
	LWDEBUGF(4, "srid=%d, start=%d, end=%d", srid, start, end);
	getPoint4d_p(pa, start, &p0);
	ptarray_set_point4d(pao, 0, &p0);	
	getPoint4d_p(pa, (start+end)/2, &p1);
	ptarray_set_point4d(pao, 1, &p1);	
	getPoint4d_p(pa, end+1, &p2);
	ptarray_set_point4d(pao, 2, &p2);	
	return lwcircstring_as_lwgeom(lwcircstring_construct(srid, NULL, pao));
}

static LWGEOM*
geom_from_pa(const POINTARRAY *pa, int srid, int is_arc, int start, int end)
{
	LWDEBUGF(4, "srid=%d, is_arc=%d, start=%d, end=%d", srid, is_arc, start, end);
	if ( is_arc )
		return circstring_from_pa(pa, srid, start, end);
	else
		return linestring_from_pa(pa, srid, start, end);
}

LWGEOM*
pta_desegmentize(POINTARRAY *points, int type, int srid)
{
	int i = 0, j, k;
	POINT4D a1, a2, a3, b;
	char *edges_in_arcs;
	int found_arc = LW_FALSE;
	int current_arc = 1;
	int num_edges;
	int edge_type = -1;
	int start, end;
	LWCOLLECTION *outcol;

	/* Die on null input */
	if ( ! points )
		lwerror("pta_desegmentize called with null pointarray");

	/* Null on empty input? */
	if ( points->npoints == 0 )
		return NULL;
	
	/* We can't desegmentize anything shorter than four points */
	if ( points->npoints < 4 )
	{
		/* Return a linestring here*/
		lwerror("pta_desegmentize needs implementation for npoints < 4");
	}
	
	/* Allocate our result array of vertices that are part of arcs */
	num_edges = points->npoints - 1;
	edges_in_arcs = lwalloc(num_edges);
	memset(edges_in_arcs, 0, num_edges);
	
	/* We make a candidate arc of the first two edges, */
	/* And then see if the next edge follows it */
	while( i < num_edges-2 )
	{
		found_arc = LW_FALSE;
		/* Make candidate arc */
		getPoint4d_p(points, i  , &a1);
		getPoint4d_p(points, i+1, &a2);
		getPoint4d_p(points, i+2, &a3);
		for( j = i+3; j < num_edges+1; j++ )
		{
			LWDEBUGF(4, "i=%d, j=%d", i, j);
			getPoint4d_p(points, j, &b);
			/* Does this point fall on our candidate arc? */
			if ( pt_continues_arc(&a1, &a2, &a3, &b) )
			{
				/* Yes. Mark this edge and the two preceding it as arc components */
				LWDEBUGF(4, "pt_continues_arc #%d", current_arc);
				found_arc = LW_TRUE;
				for ( k = j-1; k > j-4; k-- )
					edges_in_arcs[k] = current_arc;
			}
			else
			{
				/* No. So we're done with this candidate arc */
				LWDEBUG(4, "pt_continues_arc = false");
				current_arc++;
				break;
			}
		}
		/* Jump past all the edges that were added to the arc */
		if ( found_arc )
		{
			i = j-1;
		}
		else
		{
			/* Mark this edge as a linear edge */
			edges_in_arcs[i] = 0;
			i = i+1;
		}
	}
	
#if POSTGIS_DEBUG_LEVEL > 3
	{
		char *edgestr = lwalloc(num_edges+1);
		for ( i = 0; i < num_edges; i++ )
		{
			if ( edges_in_arcs[i] )
				edgestr[i] = 48 + edges_in_arcs[i];
			else
				edgestr[i] = '.';
		}
		edgestr[num_edges] = 0;
		LWDEBUGF(3, "edge pattern %s", edgestr);
		lwfree(edgestr);
	}
#endif

	start = 0;
	edge_type = edges_in_arcs[0];
	outcol = lwcollection_construct_empty(COMPOUNDTYPE, srid, ptarray_has_z(points), ptarray_has_m(points));
	for( i = 1; i < num_edges; i++ )
	{
		if( edge_type != edges_in_arcs[i] )
		{
			end = i - 1;
			lwcollection_add_lwgeom(outcol, geom_from_pa(points, srid, edge_type, start, end));
			start = i;
			edge_type = edges_in_arcs[i];
		}
	}
	/* Roll out last item */
	end = num_edges - 1;
	lwcollection_add_lwgeom(outcol, geom_from_pa(points, srid, edge_type, start, end));
	
	/* Strip down to singleton if only one entry */
	if ( outcol->ngeoms == 1 )
	{
		LWGEOM *outgeom = outcol->geoms[0];
		lwfree(outcol);
		return outgeom;
	}
	return lwcollection_as_lwgeom(outcol);
}


LWGEOM *
lwline_desegmentize(LWLINE *line)
{
	LWDEBUG(2, "lwline_desegmentize called.");

	return pta_desegmentize(line->points, line->flags, line->srid);
}

LWGEOM *
lwpolygon_desegmentize(LWPOLY *poly)
{
	LWGEOM **geoms;
	int i, hascurve = 0;

	LWDEBUG(2, "lwpolygon_desegmentize called.");

	geoms = lwalloc(sizeof(LWGEOM *)*poly->nrings);
	for (i=0; i<poly->nrings; i++)
	{
		geoms[i] = pta_desegmentize(poly->rings[i], poly->flags, poly->srid);
		if (geoms[i]->type == CIRCSTRINGTYPE || geoms[i]->type == COMPOUNDTYPE)
		{
			hascurve = 1;
		}
	}
	if (hascurve == 0)
	{
		for (i=0; i<poly->nrings; i++)
		{
			lwfree(geoms[i]);
		}
		return lwgeom_clone((LWGEOM *)poly);
	}

	return (LWGEOM *)lwcollection_construct(CURVEPOLYTYPE, poly->srid, NULL, poly->nrings, geoms);
}

LWGEOM *
lwmline_desegmentize(LWMLINE *mline)
{
	LWGEOM **geoms;
	int i, hascurve = 0;

	LWDEBUG(2, "lwmline_desegmentize called.");

	geoms = lwalloc(sizeof(LWGEOM *)*mline->ngeoms);
	for (i=0; i<mline->ngeoms; i++)
	{
		geoms[i] = lwline_desegmentize((LWLINE *)mline->geoms[i]);
		if (geoms[i]->type == CIRCSTRINGTYPE || geoms[i]->type == COMPOUNDTYPE)
		{
			hascurve = 1;
		}
	}
	if (hascurve == 0)
	{
		for (i=0; i<mline->ngeoms; i++)
		{
			lwfree(geoms[i]);
		}
		return lwgeom_clone((LWGEOM *)mline);
	}
	return (LWGEOM *)lwcollection_construct(MULTICURVETYPE, mline->srid, NULL, mline->ngeoms, geoms);
}

LWGEOM *
lwmpolygon_desegmentize(LWMPOLY *mpoly)
{
	LWGEOM **geoms;
	int i, hascurve = 0;

	LWDEBUG(2, "lwmpoly_desegmentize called.");

	geoms = lwalloc(sizeof(LWGEOM *)*mpoly->ngeoms);
	for (i=0; i<mpoly->ngeoms; i++)
	{
		geoms[i] = lwpolygon_desegmentize((LWPOLY *)mpoly->geoms[i]);
		if (geoms[i]->type == CURVEPOLYTYPE)
		{
			hascurve = 1;
		}
	}
	if (hascurve == 0)
	{
		for (i=0; i<mpoly->ngeoms; i++)
		{
			lwfree(geoms[i]);
		}
		return lwgeom_clone((LWGEOM *)mpoly);
	}
	return (LWGEOM *)lwcollection_construct(MULTISURFACETYPE, mpoly->srid, NULL, mpoly->ngeoms, geoms);
}

LWGEOM *
lwgeom_desegmentize(LWGEOM *geom)
{
	LWDEBUG(2, "lwgeom_desegmentize called.");

	switch (geom->type)
	{
	case LINETYPE:
		return lwline_desegmentize((LWLINE *)geom);
	case POLYGONTYPE:
		return lwpolygon_desegmentize((LWPOLY *)geom);
	case MULTILINETYPE:
		return lwmline_desegmentize((LWMLINE *)geom);
	case MULTIPOLYGONTYPE:
		return lwmpolygon_desegmentize((LWMPOLY *)geom);
	default:
		return lwgeom_clone(geom);
	}
}