Datum LWGEOM_line_interpolate_point(PG_FUNCTION_ARGS)
{
GSERIALIZED *geom = (GSERIALIZED *)PG_DETOAST_DATUM(PG_GETARG_DATUM(0));
double distance = PG_GETARG_FLOAT8(1);
LWLINE *line;
LWPOINT *point;
POINTARRAY *ipa, *opa;
POINT4D pt;
int nsegs, i;
double length, slength, tlength;
if ( distance < 0 || distance > 1 )
{
elog(ERROR,"line_interpolate_point: 2nd arg isnt within [0,1]");
PG_RETURN_NULL();
}
if ( gserialized_get_type(geom) != LINETYPE )
{
elog(ERROR,"line_interpolate_point: 1st arg isnt a line");
PG_RETURN_NULL();
}
line = lwgeom_as_lwline(lwgeom_from_gserialized(geom));
ipa = line->points;
/* If distance is one of the two extremes, return the point on that
* end rather than doing any expensive computations
*/
if ( distance == 0.0 || distance == 1.0 )
{
if ( distance == 0.0 )
getPoint4d_p(ipa, 0, &pt);
else
getPoint4d_p(ipa, ipa->npoints-1, &pt);
opa = ptarray_construct_reference_data(FLAGS_GET_Z(line->flags), FLAGS_GET_M(line->flags), 1, (uint8_t*)&pt);
point = lwpoint_construct(line->srid, NULL, opa);
PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
}
/* Interpolate a point on the line */
nsegs = ipa->npoints - 1;
length = ptarray_length_2d(ipa);
tlength = 0;
for ( i = 0; i < nsegs; i++ )
{
POINT4D p1, p2;
POINT4D *p1ptr=&p1, *p2ptr=&p2; /* don't break
* strict-aliasing rules
*/
getPoint4d_p(ipa, i, &p1);
getPoint4d_p(ipa, i+1, &p2);
/* Find the relative length of this segment */
slength = distance2d_pt_pt((POINT2D*)p1ptr, (POINT2D*)p2ptr)/length;
/* If our target distance is before the total length we've seen
* so far. create a new point some distance down the current
* segment.
*/
if ( distance < tlength + slength )
{
double dseg = (distance - tlength) / slength;
interpolate_point4d(&p1, &p2, &pt, dseg);
opa = ptarray_construct_reference_data(FLAGS_GET_Z(line->flags), FLAGS_GET_M(line->flags), 1, (uint8_t*)&pt);
point = lwpoint_construct(line->srid, NULL, opa);
PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
}
tlength += slength;
}
/* Return the last point on the line. This shouldn't happen, but
* could if there's some floating point rounding errors. */
getPoint4d_p(ipa, ipa->npoints-1, &pt);
opa = ptarray_construct_reference_data(FLAGS_GET_Z(line->flags), FLAGS_GET_M(line->flags), 1, (uint8_t*)&pt);
point = lwpoint_construct(line->srid, NULL, opa);
PG_RETURN_POINTER(geometry_serialize(lwpoint_as_lwgeom(point)));
}
POINTARRAY *
ptarray_substring(POINTARRAY *ipa, double from, double to, double tolerance)
{
POINTARRAY *dpa;
POINT4D pt;
POINT4D p1, p2;
POINT4D *p1ptr=&p1; /* don't break strict-aliasing rule */
POINT4D *p2ptr=&p2;
int nsegs, i;
double length, slength, tlength;
int state = 0; /* 0=before, 1=inside */
/*
* Create a dynamic pointarray with an initial capacity
* equal to full copy of input points
*/
dpa = ptarray_construct_empty(FLAGS_GET_Z(ipa->flags), FLAGS_GET_M(ipa->flags), ipa->npoints);
/* Compute total line length */
length = ptarray_length_2d(ipa);
LWDEBUGF(3, "Total length: %g", length);
/* Get 'from' and 'to' lengths */
from = length*from;
to = length*to;
LWDEBUGF(3, "From/To: %g/%g", from, to);
tlength = 0;
getPoint4d_p(ipa, 0, &p1);
nsegs = ipa->npoints - 1;
for ( i = 0; i < nsegs; i++ )
{
double dseg;
getPoint4d_p(ipa, i+1, &p2);
LWDEBUGF(3 ,"Segment %d: (%g,%g,%g,%g)-(%g,%g,%g,%g)",
i, p1.x, p1.y, p1.z, p1.m, p2.x, p2.y, p2.z, p2.m);
/* Find the length of this segment */
slength = distance2d_pt_pt((POINT2D *)p1ptr, (POINT2D *)p2ptr);
/*
* We are before requested start.
*/
if ( state == 0 ) /* before */
{
LWDEBUG(3, " Before start");
if ( fabs ( from - ( tlength + slength ) ) <= tolerance )
{
LWDEBUG(3, " Second point is our start");
/*
* Second point is our start
*/
ptarray_append_point(dpa, &p2, LW_FALSE);
state=1; /* we're inside now */
goto END;
}
else if ( fabs(from - tlength) <= tolerance )
{
LWDEBUG(3, " First point is our start");
/*
* First point is our start
*/
ptarray_append_point(dpa, &p1, LW_FALSE);
/*
* We're inside now, but will check
* 'to' point as well
*/
state=1;
}
/*
* Didn't reach the 'from' point,
* nothing to do
*/
else if ( from > tlength + slength ) goto END;
else /* tlength < from < tlength+slength */
{
LWDEBUG(3, " Seg contains first point");
/*
* Our start is between first and
* second point
*/
dseg = (from - tlength) / slength;
interpolate_point4d(&p1, &p2, &pt, dseg);
ptarray_append_point(dpa, &pt, LW_FALSE);
/*
* We're inside now, but will check
* 'to' point as well
*/
state=1;
}
}
if ( state == 1 ) /* inside */
{
LWDEBUG(3, " Inside");
/*
* 'to' point is our second point.
*/
if ( fabs(to - ( tlength + slength ) ) <= tolerance )
{
LWDEBUG(3, " Second point is our end");
ptarray_append_point(dpa, &p2, LW_FALSE);
break; /* substring complete */
}
/*
* 'to' point is our first point.
* (should only happen if 'to' is 0)
*/
else if ( fabs(to - tlength) <= tolerance )
{
LWDEBUG(3, " First point is our end");
ptarray_append_point(dpa, &p1, LW_FALSE);
break; /* substring complete */
}
/*
* Didn't reach the 'end' point,
* just copy second point
*/
else if ( to > tlength + slength )
{
ptarray_append_point(dpa, &p2, LW_FALSE);
goto END;
}
/*
* 'to' point falls on this segment
* Interpolate and break.
*/
else if ( to < tlength + slength )
{
LWDEBUG(3, " Seg contains our end");
dseg = (to - tlength) / slength;
interpolate_point4d(&p1, &p2, &pt, dseg);
ptarray_append_point(dpa, &pt, LW_FALSE);
break;
}
else
{
LWDEBUG(3, "Unhandled case");
}
}
END:
tlength += slength;
memcpy(&p1, &p2, sizeof(POINT4D));
}
LWDEBUGF(3, "Out of loop, ptarray has %d points", dpa->npoints);
return dpa;
}
