A lower priority bug is that the renderer is an idealized globe rather than an ellipsoid.
It requires a bit of thought to handle mercator as well if we're distorting tiles. It may be best to fix the other issue with gudermannian first. Perhaps it is best to leave tiles on an ellipsoid and to correct the images beforehand separately.
https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/Ellipsoid.js#L85 https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/Ellipsoid.js#L386
A lower priority bug is that the renderer is an idealized globe rather than an ellipsoid.
It requires a bit of thought to handle mercator as well if we're distorting tiles. It may be best to fix the other issue with gudermannian first. Perhaps it is best to leave tiles on an ellipsoid and to correct the images beforehand separately.
https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/Ellipsoid.js#L85 https://github.com/AnalyticalGraphicsInc/cesium/blob/master/Source/Core/Ellipsoid.js#L386