+- Gimp-Forum.net (https://www.gimp-forum.net)
+-- Forum: GIMP (https://www.gimp-forum.net/Forum-GIMP)
+--- Forum: General questions (https://www.gimp-forum.net/Forum-General-questions)
+--- Thread: Circle to Rectangle (/Thread-Circle-to-Rectangle)
Circle to Rectangle - Whitewings - 10-14-2023
I have an old-style two-circles map, similar to the one here:
![[Image: default.jpg]](https://tile.loc.gov/image-services/iiif/service:gmd:gmd3:g3200:g3200:ct007061/full/pct:12.5/0/default.jpg)
I've extracted the circles, and now need to turn them into squares so I can use them as a texture in a render. I've tried various techniques: warp, cage and scale transforms, and scale layer in the layer menu; either they're the wrong tools or I'm not using them properly; is there a way to actually do this?
RE: Circle to Rectangle - Ofnuts - 10-14-2023
(10-14-2023, 05:31 AM)Whitewings Wrote: I have an old-style two-circles map, similar to the one here:
I've extracted the circles, and now need to turn them into squares so I can use them as a texture in a render. I've tried various techniques: warp, cage and scale transforms, and scale layer in the layer menu; either they're the wrong tools or I'm not using them properly; is there a way to actually do this?
What do you expect the result to be? If you are trying to achieve the usual "Mercator" look you have to stretch the pole points into lines and this won't be pretty.
Edit: since you asked on StackOverflow (so I can assume a programming background): you can in theory come up with a "displace map" that will undo the transform (actually, a pair of maps, one for X and one for Y). I have used this with some success (but in a somewhat simpler case).
RE: Circle to Rectangle - rich2005 - 10-14-2023
Similar comment to above, If you want to convert the equidistant projection to say a transverse mercator where latitude and longitude grid is rectangular then there might be some clever web application somewhere.
EDIT: Sorry, failed to notice your MacOS system. No gmic plugin for you.
You can get a rectangular image using the gimp_gmic_qt plugin http://www.gmic.eu filter square-to-circle / circle-to-square looks like this:
[attachment=10487]
RE: Circle to Rectangle - denzjos - 10-14-2023
Some explanation about this matter :
https://squircular.blogspot.com/2015/09/elliptical-arc-mapping.html
https://arxiv.org/ftp/arxiv/papers/1709/1709.07875.pdf
RE: Circle to Rectangle - Whitewings - 10-14-2023
(10-14-2023, 07:58 AM)denzjos Wrote: Some explanation about this matter :
https://squircular.blogspot.com/2015/09/elliptical-arc-mapping.html
The upper illustration is exactly what I want to do.