[geos-devel] CoordinateSequence::reverse(CoordinateSequence *cl) bug

[Elliott Edwards]

Greetings all.

I am not certain that this issue hasn't already been addressed, but I 
thought that I would submit it anyway.

//The existing version
void CoordinateSequence::reverse(CoordinateSequence *cl){
	int last=cl->getSize()-1;
	int mid=last/2;
	for(int i=0;i<=mid;i++) {
		const Coordinate& tmp=cl->getAt(i);
		cl->setAt(cl->getAt(last-i),i);
		cl->setAt(tmp,last-i);
	}
}

The result of this code is not to reverse the coordinate sequence, but 
rather to reflect the first half of it.

Ex: If A-Z are coordinates:

A B C D E F G

would incorrectly become

A B C D C B A

instead of

G F E D C B A

This is a result of the "tmp" variable being a "Coordinate&" rather than 
  a "Coordinate".

//The corrected version
void CoordinateSequence::reverse(CoordinateSequence *cl){
	int last=cl->getSize()-1;
	int mid=last/2;
	for(int i=0;i<=mid;i++) {
		const Coordinate tmp=cl->getAt(i);
		cl->setAt(cl->getAt(last-i),i);
		cl->setAt(tmp,last-i);
	}
}

Note: This also affects the correctness of Polygon::normalize() because 
it uses the CoordinateSequence::reverse to normalize the polygon winding.

Please disregard this message if this issue has already been resolved or 
a resolution is in the works.

-Elliott Edwards-