PNG to StereoProjection

Someone asked me "Is there an easy way to change the image being projected?"

Yes, we can use the `surface()` operation to load an image, and then perform the `projection()` operation to get a 2D object. After that, my `stereographic_projection()` module can make a stereographic projection from the 2D object. The solution works but the `projection()` operation is slow.


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- *[OpenSCAD Documentation - Traditional Chinese](https://openhome.cc/Gossip/OpenSCAD/)*
- *[OpenSCAD Documentati