Prepared Contains mismatch with Contains

[pramsey]

As reported at https://trac.osgeo.org/postgis/ticket/5634. The issue is in GEOS prepared geometry.

A test for PreparedGeometryTest.cpp:

template<>
template<>
void object::test<3>
()
{
    g1 = reader.read( "MULTIPOLYGON(((-60 -50,-70 -50,-60 -40,-60 -50)))" );
    g2 = reader.read( "GEOMETRYCOLLECTION(MULTIPOINT((-60 -50),(-63 -49)))" );

    pg1 = prep::PreparedGeometryFactory::prepare(g1.get());

    ensure(  g1->contains(g2.get()) );
    ensure( pg1->contains(g2.get()) );
}

[pramsey]

Seems to require the double nesting to exercise the bug, both

MULTIPOINT((-60 -50),(-63 -49))

and

GEOMETRYCOLLECTION(POINT(-60 -50),POINT(-63 -49))

work as variations on the second argument.

[pramsey]

@cuteDen-ECNU as a general proposition, every prepared variant should return the same as the non-prepared variant, I imagine there's a lot of possible issues hiding in that proposition.

[dr-jts]

Tests expressed with geosop:

bin/geosop -a "MULTIPOLYGON(((-60 -50,-70 -50,-60 -40,-60 -50)))" -b "GEOMETRYCOLLECTION(MULTIPOINT((-60 -50),(-63 -49)))" contains
==> true

bin/geosop -a "MULTIPOLYGON(((-60 -50,-70 -50,-60 -40,-60 -50)))" -b "GEOMETRYCOLLECTION(MULTIPOINT((-60 -50),(-63 -49)))" containsPrep
==> false

I thought this might be related to #982, but in fact in this case the contains result is correct, but the preparedContains result is wrong. Also, "unwrapping" the MULTIPOINT produces the correct result:

bin/geosop -a "MULTIPOLYGON(((-60 -50,-70 -50,-60 -40,-60 -50)))" -b "MULTIPOINT((-60 -50),(-63 -49))" containsPrep 
==>true

Further investigation is required.

[cuteDen-ECNU]

as a general proposition, every prepared variant should return the same as the non-prepared variant, I imagine there's a lot of possible issues hiding in that proposition.

I agree with you. I am refining my tool to focus on this kind of issue.

[dr-jts]

The problem is caused by this line in AbstractPreparedPolygonContains:

if (geom->getNumGeometries() > 1) {

This does not handle GeometryCollections which contain one element which itself contains multiple elements.

A simple fix is to replace getNumGeometries with getNumPoints.