How can I create a normal map that points 90 degrees upward from a flat surface? Basically, I would like to have a cross billboard (such as the one below) have it's lighting come from above it. In other words, I would like the lighting to be as if the sunshine was hitting it from above.



The intention is for the billboard - Which will have a grass texture on it - To take lighting from the same direction as the terrain underneath.

The best way to do this, I believe, would appear to be with a normal map, making all 4 faces take lighting from 90 degrees upward.

Would this be possible to do with Blender?
Normal maps are not necessarily for adding detail but to change the way light falls on the surface. Here is a quick example of changed normal map without changing the detail using the Normal node:



Here is an alternative with the normal map generated dynamically by calculating the direction between the object and the light (Can I refer to another object&#39;s properties from a Cycles node shader? Drivers? If so, how?):




Watch this excellent tutorial by 
Zacharias Reinhardt
https://www.youtube.com/watch?v=BtUS8QTsVZA&amp;index=4&amp;list=PLGodxM8aVtUfH9_xv4OdMM4xvBGZpggoA

in a nutshell, you have to


create your full object with material first
render it in ortho on a square plane
generate normal map and color texture for this square projection
use the normal and color textures as material for your "cross billboard"


To get a proper shadow is more complicated but can be achieved as per the great trick of part 2 of the video by Zacharias Reinhardt!