Currently triplanar uses a square mapping, even when the input bitmap is rectangular. The way to deal with this is to manually control the tiling. But it'd be better to have the triplanar map do this automatically by simply adding a check box.
Please note that CMAX-1342 is "Fit to bitmap" button in CoronaBitmap. It makes sens to have a checkbox in Triplanar, which is on by default, which ignores Bitmap/CoronaBitmap's mapping (because RWS is tricky, as tiling value of 1.0 is triplanars actual size) and just maps the set size as real world width of the texture, height is calculated automatically based on this. This, triplanar specific request is reported at: https://jira-chaos.atlassian.net/browse/CMAX-1192
Please note that CMAX-1342 is "Fit to bitmap" button in CoronaBitmap. It makes sens to have a checkbox in Triplanar, which is on by default, which ignores Bitmap/CoronaBitmap's mapping (because RWS is tricky, as tiling value of 1.0 is triplanars actual size) and just maps the set size as real world width of the texture, height is calculated automatically based on this. This, triplanar specific request is reported at: https://jira-chaos.atlassian.net/browse/CMAX-1192