vertices.add(vectorXYZForPointAt(leftXIndex, bottomZIndex));
vertices.add(vectorXYZForPointAt(leftXIndex+1, bottomZIndex));
vertices.add(vectorXYZForPointAt(leftXIndex+1, bottomZIndex+1));
vertices.add(vectorXYZForPointAt(leftXIndex, bottomZIndex+1));
vertices.add(vertices.get(0));
return new PolygonXYZ(vertices);
}