Datum ST_AddMeasure(PG_FUNCTION_ARGS)
{
GSERIALIZED *gin = PG_GETARG_GSERIALIZED_P(0);
GSERIALIZED *gout;
double start_measure = PG_GETARG_FLOAT8(1);
double end_measure = PG_GETARG_FLOAT8(2);
LWGEOM *lwin, *lwout;
int type = gserialized_get_type(gin);
/* Raise an error if input is not a linestring or multilinestring */
if ( type != LINETYPE && type != MULTILINETYPE )
{
lwpgerror("Only LINESTRING and MULTILINESTRING are supported");
PG_RETURN_NULL();
}
lwin = lwgeom_from_gserialized(gin);
if ( type == LINETYPE )
lwout = (LWGEOM*)lwline_measured_from_lwline((LWLINE*)lwin, start_measure, end_measure);
else
lwout = (LWGEOM*)lwmline_measured_from_lwmline((LWMLINE*)lwin, start_measure, end_measure);
lwgeom_free(lwin);
if ( lwout == NULL )
PG_RETURN_NULL();
gout = geometry_serialize(lwout);
lwgeom_free(lwout);
PG_RETURN_POINTER(gout);
}
/**
* Re-write the measure ordinate (or add one, if it isn't already there) interpolating
* the measure between the supplied start and end values.
*/
LWMLINE*
lwmline_measured_from_lwmline(const LWMLINE *lwmline, double m_start, double m_end)
{
int i = 0;
int hasm = 0, hasz = 0;
double length = 0.0, length_so_far = 0.0;
double m_range = m_end - m_start;
LWGEOM **geoms = NULL;
if ( lwmline->type != MULTILINETYPE )
{
lwerror("lwmline_measured_from_lmwline: only multiline types supported");
return NULL;
}
hasz = FLAGS_GET_Z(lwmline->flags);
hasm = 1;
/* Calculate the total length of the mline */
for ( i = 0; i < lwmline->ngeoms; i++ )
{
LWLINE *lwline = (LWLINE*)lwmline->geoms[i];
if ( lwline->points && lwline->points->npoints > 1 )
{
length += ptarray_length_2d(lwline->points);
}
}
if ( lwgeom_is_empty((LWGEOM*)lwmline) )
{
return (LWMLINE*)lwcollection_construct_empty(MULTILINETYPE, lwmline->srid, hasz, hasm);
}
geoms = lwalloc(sizeof(LWGEOM*) * lwmline->ngeoms);
for ( i = 0; i < lwmline->ngeoms; i++ )
{
double sub_m_start, sub_m_end;
double sub_length = 0.0;
LWLINE *lwline = (LWLINE*)lwmline->geoms[i];
if ( lwline->points && lwline->points->npoints > 1 )
{
sub_length = ptarray_length_2d(lwline->points);
}
sub_m_start = (m_start + m_range * length_so_far / length);
sub_m_end = (m_start + m_range * (length_so_far + sub_length) / length);
geoms[i] = (LWGEOM*)lwline_measured_from_lwline(lwline, sub_m_start, sub_m_end);
length_so_far += sub_length;
}
return (LWMLINE*)lwcollection_construct(lwmline->type, lwmline->srid, NULL, lwmline->ngeoms, geoms);
}
static LWMPOINT*
lwline_locate_along(const LWLINE *lwline, double m, double offset)
{
POINTARRAY *opa = NULL;
LWMPOINT *mp = NULL;
LWGEOM *lwg = lwline_as_lwgeom(lwline);
int hasz, hasm, srid;
/* Return degenerates upwards */
if ( ! lwline ) return NULL;
/* Create empty return shell */
srid = lwgeom_get_srid(lwg);
hasz = lwgeom_has_z(lwg);
hasm = lwgeom_has_m(lwg);
if ( hasm )
{
/* Find points along */
opa = ptarray_locate_along(lwline->points, m, offset);
}
else
{
LWLINE *lwline_measured = lwline_measured_from_lwline(lwline, 0.0, 1.0);
opa = ptarray_locate_along(lwline_measured->points, m, offset);
lwline_free(lwline_measured);
}
/* Return NULL as EMPTY */
if ( ! opa )
return lwmpoint_construct_empty(srid, hasz, hasm);
/* Convert pointarray into a multipoint */
mp = lwmpoint_construct(srid, opa);
ptarray_free(opa);
return mp;
}
