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/**********************************************************************
*
* PostGIS - Spatial Types for PostgreSQL
* http://postgis.net
*
* PostGIS is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License, or
* (at your option) any later version.
*
* PostGIS is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with PostGIS. If not, see <http://www.gnu.org/licenses/>.
*
**********************************************************************
*
* Copyright 2014 Kashif Rasul <kashif.rasul@gmail.com> and
*
**********************************************************************/
#include "stringbuffer.h"
#include "liblwgeom_internal.h"
static char * lwline_to_encoded_polyline(const LWLINE*, int precision);
static char * lwmmpoint_to_encoded_polyline(const LWMPOINT*, int precision);
static char * pointarray_to_encoded_polyline(const POINTARRAY*, int precision);
/* takes a GEOMETRY and returns an Encoded Polyline representation */
extern char *
lwgeom_to_encoded_polyline(const LWGEOM *geom, int precision)
{
int type = geom->type;
switch (type)
{
case LINETYPE:
return lwline_to_encoded_polyline((LWLINE*)geom, precision);
case MULTIPOINTTYPE:
return lwmmpoint_to_encoded_polyline((LWMPOINT*)geom, precision);
default:
lwerror("lwgeom_to_encoded_polyline: '%s' geometry type not supported", lwtype_name(type));
return NULL;
}
}
static
char * lwline_to_encoded_polyline(const LWLINE *line, int precision)
{
return pointarray_to_encoded_polyline(line->points, precision);
}
static
char * lwmmpoint_to_encoded_polyline(const LWMPOINT *mpoint, int precision)
{
LWLINE *line = lwline_from_lwmpoint(mpoint->srid, mpoint);
char *encoded_polyline = lwline_to_encoded_polyline(line, precision);
lwline_free(line);
return encoded_polyline;
}
static
char * pointarray_to_encoded_polyline(const POINTARRAY *pa, int precision)
{
int i;
const POINT2D *prevPoint;
int *delta = lwalloc(2*sizeof(int)*pa->npoints);
char *encoded_polyline = NULL;
stringbuffer_t *sb;
double scale = pow(10,precision);
/* Take the double value and multiply it by 1x10^percision, rounding the result */
prevPoint = getPoint2d_cp(pa, 0);
delta[0] = round(prevPoint->y*scale);
delta[1] = round(prevPoint->x*scale);
/* points only include the offset from the previous point */
for (i=1; i<pa->npoints; i++)
{
const POINT2D *point = getPoint2d_cp(pa, i);
delta[2*i] = round(point->y*scale) - round(prevPoint->y*scale);
delta[(2*i)+1] = round(point->x*scale) - round(prevPoint->x*scale);
prevPoint = point;
}
/* value to binary: a negative value must be calculated using its two's complement */
for (i=0; i<pa->npoints*2; i++)
{
/* Left-shift the binary value one bit */
delta[i] <<= 1;
/* if value is negative, invert this encoding */
if (delta[i] < 0) {
delta[i] = ~(delta[i]);
}
}
sb = stringbuffer_create();
for (i=0; i<pa->npoints*2; i++)
{
int numberToEncode = delta[i];
while (numberToEncode >= 0x20) {
/* Place the 5-bit chunks into reverse order or
each value with 0x20 if another bit chunk follows and add 63*/
int nextValue = (0x20 | (numberToEncode & 0x1f)) + 63;
stringbuffer_aprintf(sb, "%c", (char)nextValue);
if(92 == nextValue)
stringbuffer_aprintf(sb, "%c", (char)nextValue);
/* Break the binary value out into 5-bit chunks */
numberToEncode >>= 5;
}
numberToEncode += 63;
stringbuffer_aprintf(sb, "%c", (char)numberToEncode);
if(92 == numberToEncode)
stringbuffer_aprintf(sb, "%c", (char)numberToEncode);
}
lwfree(delta);
encoded_polyline = stringbuffer_getstringcopy(sb);
stringbuffer_destroy(sb);
return encoded_polyline;
}
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