Does Cesium support the .dds file format in ImageLayers from e.g. a UrlTemplateImageryProvider()?
Short answer: No, but only because no browser that I know of supports dds images. UrlTemplateImageryProvider supports whatever images the underlying browser supports.
Details:
As bizarre as it may sound, the HTML specification does not state what image formats are standard or must be supported, so support is browser dependent. In most cases, jpg, gif, and png are the only 3 types you can rely on cross-browser. (even svg is still kind of flaky in my opinion).
Cesium’s imagery system is pretty flexible, so you could technically write a plug-in that decodes dds images onto a canvas (which Cesium can then draw on the globe) but in practice you would be better off converting to something else server-side ahead of time (or on the fly and caching).
Makes total sense.
There’s no real reason (other than inconvenience) that we can’t and shouldn’t convert all of the images to e.g. .png and have them live side-by-side our .dds images.
Imagemagick is my new best friend…