A union including about 3200 shapes will be very slow. OpenSCAD does not seem to use any optimization for non-intersection arrangements. I did some testing on that, and results <http://forum.openscad.org/No-bounding-box-test-for-union-before-entering-CGAL-tp17538.html> were discouraging. I just did some fast test also for your code, using the first 200 of your polygons and measured how long F6 will take. It took about 80s, which means, that with suspected O(n²) full rendering will take about 6h. BTW it is not worth investing this time, because I got (as expected): WARNING: Object may not be a valid 2-manifold and may need repair! This is because of numeric problems with shapes having closely adjacent faces, not being matched exactly. Don't know how good your programming is. In cases like this, you always have the option to compose the full shape on your own by use of polyhedron. This means, you have to either retrieve or calculate neighborhood relations first to be able to do the facing. I don't see more land with current OpenSCAD. What about using Blender? -- View this message in context: http://forum.openscad.org/Advice-optimizing-render-for-large-object-tp17571p17573.html Sent from the OpenSCAD mailing list archive at Nabble.com.