id,summary,reporter,owner,description,type,status,priority,milestone,component,version,severity,resolution,keywords,cc
2174,Problem with RingExtent::calculate in shape2ogr.cpp,bpeschel,rouault,"I am using code from shape2ogr.cpp to determine outer/inner rings and their association.  The method RingExtent::calculate() is used to find the max and min of the object.  This is used later to check if the inner rings are contained by the inner.

However, the code has a bug in it:
{{{
void RingExtent::calculate( int ringParts, double *ringX, double *ringY )
{
    empty = ringParts <= 0;
    if ( !empty )
    {
        xMin = xMax = *ringX;
        yMin = yMax = *ringY;
        while( --ringParts > 0 )
        {
            if ( xMin > *ringX )
                xMin = *ringX;
            else if ( xMax < *ringX )
                xMax = *ringX;
            if ( yMin > *ringY )
               yMin = *ringY;
            else if ( yMax < *ringY )
                yMax = *ringY;
            ++ringX;
            ++ringY;
        }
    }
}
}}}
The problem is in the while loop.  Because SHPReadOGRObject() calls this by:
{{{
 int start = 0;
 int end = 0;
 RingStartEnd ( psShape, iRing, &start, &end );
 extents[ iRing ].calculate( end-start, psShape->padfX + start, psShape->padfY + start );
}}}

So, if the ring has 4 points (causing 5 in the shape file because the first and last must be repeated), start would be 0 and end would be 4.  So, the loop will evaluate points 0, 1, and 2 skipping the fourth point.  If that point happens to be a max or min, the later calculations will not be correct.

It appears this can be fixed by changing
        while( --ringParts > 0 )
to
        while( ringParts-- > 0 )
at least in my limited testing.

If I can attach a file after submission, I will attach a shapefile set that proves this.
",defect,closed,normal,1.6.0,default,unspecified,normal,fixed,,warmerdam