Displaying offsets is pretty simple - just tessellate the sphere, add offsets to the vertex positions based on the height selected from the maps, and draw the rays in all parts.
How far is the camera from the sphere / earth? If you're right at the surface, you probably shouldn't make a whole “sphere” at all, just create a “height field”. If you are far away (immediately viewing the entire planet), then even the highest mountains should not noticeably move the surface, so instead you should use a simple bump display. Think also, using a combination - rough tessellation, which is really crowded out, and display the image on the difference in the residual height.
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