2014-07-07 10:21:22 +00:00
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/**********************************************************************
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*
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* PostGIS - Spatial Types for PostgreSQL
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* http://postgis.net
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*
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* Copyright 2014 Kashif Rasul <kashif.rasul@gmail.com> and
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* Shoaib Burq <saburq@gmail.com>
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*
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* This is free software; you can redistribute and/or modify it under
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* the terms of the GNU General Public Licence. See the COPYING file.
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*
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**********************************************************************/
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#include "stringbuffer.h"
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#include "liblwgeom_internal.h"
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static char * lwline_to_encoded_polyline(const LWLINE*, int precision);
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static char * lwmmpoint_to_encoded_polyline(const LWMPOINT*, int precision);
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static char * pointarray_to_encoded_polyline(const POINTARRAY*, int precision);
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/* takes a GEOMETRY and returns an Encoded Polyline representation */
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extern char *
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lwgeom_to_encoded_polyline(const LWGEOM *geom, int precision)
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{
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int type = geom->type;
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switch (type)
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{
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case LINETYPE:
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return lwline_to_encoded_polyline((LWLINE*)geom, precision);
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case MULTIPOINTTYPE:
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return lwmmpoint_to_encoded_polyline((LWMPOINT*)geom, precision);
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default:
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lwerror("lwgeom_to_encoded_polyline: '%s' geometry type not supported", lwtype_name(type));
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return NULL;
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}
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}
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static
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char * lwline_to_encoded_polyline(const LWLINE *line, int precision)
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{
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return pointarray_to_encoded_polyline(line->points, precision);
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}
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static
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char * lwmmpoint_to_encoded_polyline(const LWMPOINT *mpoint, int precision)
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{
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LWLINE *line = lwline_from_lwmpoint(mpoint->srid, mpoint);
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char *encoded_polyline = lwline_to_encoded_polyline(line, precision);
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lwline_free(line);
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return encoded_polyline;
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}
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static
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char * pointarray_to_encoded_polyline(const POINTARRAY *pa, int precision)
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{
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int i;
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2014-07-07 22:53:43 +00:00
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const POINT2D *prevPoint;
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2014-07-07 22:44:15 +00:00
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int *delta = lwalloc(2*sizeof(int)*pa->npoints);
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2014-07-07 10:21:22 +00:00
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char *encoded_polyline = NULL;
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stringbuffer_t *sb;
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double scale = pow(10,precision);
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/* Take the double value and multiply it by 1x10^percision, rounding the result */
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prevPoint = getPoint2d_cp(pa, 0);
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delta[0] = round(prevPoint->y*scale);
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delta[1] = round(prevPoint->x*scale);
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/* points only include the offset from the previous point */
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for (i=1; i<pa->npoints; i++)
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{
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const POINT2D *point = getPoint2d_cp(pa, i);
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delta[2*i] = round(point->y*scale) - round(prevPoint->y*scale);
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delta[(2*i)+1] = round(point->x*scale) - round(prevPoint->x*scale);
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prevPoint = point;
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}
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/* value to binary: a negative value must be calculated using its two's complement */
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for (i=0; i<pa->npoints*2; i++)
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{
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/* Left-shift the binary value one bit */
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delta[i] <<= 1;
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/* if value is negative, invert this encoding */
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if (delta[i] < 0) {
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delta[i] = ~(delta[i]);
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}
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}
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sb = stringbuffer_create();
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for (i=0; i<pa->npoints*2; i++)
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{
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int numberToEncode = delta[i];
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while (numberToEncode >= 0x20) {
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/* Place the 5-bit chunks into reverse order or
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each value with 0x20 if another bit chunk follows and add 63*/
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int nextValue = (0x20 | (numberToEncode & 0x1f)) + 63;
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stringbuffer_aprintf(sb, "%c", (char)nextValue);
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if(92 == nextValue)
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stringbuffer_aprintf(sb, "%c", (char)nextValue);
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/* Break the binary value out into 5-bit chunks */
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numberToEncode >>= 5;
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}
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numberToEncode += 63;
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stringbuffer_aprintf(sb, "%c", (char)numberToEncode);
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if(92 == numberToEncode)
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stringbuffer_aprintf(sb, "%c", (char)numberToEncode);
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}
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2014-07-07 22:44:15 +00:00
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lwfree(delta);
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2014-07-07 10:21:22 +00:00
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encoded_polyline = stringbuffer_getstringcopy(sb);
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stringbuffer_destroy(sb);
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return encoded_polyline;
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}
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