In case anybody still need it. The Z value of the scene capture doesn’t change anything (as long as it’s not below the landscape).
Ortho width is the size of your landscape. If your landscape is 25200x25200 units, then set it to 25200
There’s still something I don’t understand about The Witcher 3 “pigment map”.
Their world is HUGE (74km²) and when trying to use this technic with a world half of this size, it’s doesn’t even work very well.
With a 20482048 scene capture texture, one pixel is something like 200 m² on the landscape so if you paint a 50m² circle of dry grass, the grass still look like grass 50m away because it’s smaller than a pixel on the texture capture.
Going over 40964096 scene capture texture result in insane sized texture (4k=130Mb, 8k = 524Mb, absolutly unusable) so I wonder how they get such precision in their “pigment map”