Hi Reck :
1) select 'spherical' in the camera option (default is perspective)
2) set camera rotation angle to 0,0,0
3) probably increase the sun disk (light sun option) a little bit to avoid out of range value : 0.6-0.7 should work fine (default 0.5).
4) use an image ratio 2 (something like 1024 * 512)
5) render and save as .exr
Here a example using only Terragen image as only light source in Modo (with importance sampling activated.
The sundisk is responsible of the sharp shadow.