DistanceOp result failed

[xavierraffin]

When I tried to calculate a projection of a point on a linestring I have got an bad distance result.

When I compiled with -g and without gcc optimisation, the error doesn't appear !'''

This is an extract of my code :

boost::shared_ptr<geos::geom::Linestring> line = ...;
boost::shared_ptr<geos::geom::Point> point = ...;
...
double distance line->distance(point);

Here distance is 64.9363 if compiled in debug (-g and no -O) mode. but distance is 1.79769e+308 if compiled in release mode (without -g and with -O3).

So I looked at the geos source code.

First the distance function in Geometry

double
Geometry::distance(const Geometry *other) const
{
	return DistanceOp::distance(this, other);
}

So I looked at DistanceOp.cpp and see (in computeFacetDistance):

PointExtracter::getPoints(*(geom[1]),pts1);

with GEOS_DEBUG activated I see in debug mode:

PointExtracter found 0 points in geometry 1 and 1 points in geometry 2

and in release mode

PointExtracter found 0 points in geometry 1 and 0 points in geometry 2

The issue is that in release mode the second Geometry object (the Point) is not detected as a point.

So I go further and see that PointExtracter::getPoints static method call a Point method apply_ro wich call in return PointExtracter (subclass of GeometryFilter) method apply_ro.

The code is (PointExtracter.h):

        void filter_ro(const Geometry *geom)
        {
if ( const Point *p=dynamic_cast<const Point *>(geom) )
                comps.push_back(p);
        }

So I add some trace and see that in release mode the PointExtracter::filter_ro method wasn't called by Point::filter_ro (in debug that works).

So I change DistanceOp.cpp to use non-static method instead of the static one (see joined patch).

That solve the issue.

Patch is very short:

===================================================================
--- 3rd/dev/geos/src/operation/distance/DistanceOp.cpp  (révision 3499)
+++ 3rd/dev/geos/src/operation/distance/DistanceOp.cpp  (copie de travail)
@@ -402,8 +402,12 @@

        Point::ConstVect pts0;
        Point::ConstVect pts1;
-       PointExtracter::getPoints(*(geom[0]), pts0);
-       PointExtracter::getPoints(*(geom[1]), pts1);
+
+       PointExtracter pe(pts0);
+       geom[0]->apply_ro(&pe);
+
+       PointExtracter pe1(pts1);
+       geom[1]->apply_ro(&pe1);

 #if GEOS_DEBUG
        std::cerr << "PointExtracter found "

I can add that I try using valgrind to detect some memory errors but I found nothing.

My source code is branches/3.2 rev 3477.

Regards,

Xavier Raffin

[xavierraffin]

patch

[strk]

No more support for 3.2 branch