I'm getting a "Illegal grid value in dda_traversal()".

### 9.5.2 I'm getting a "Illegal grid value in dda_traversal()".

"When I render a height field I get lots of warning messages saying "Illegal grid value in dda_traversal()". How can I correct that?"

(Answer by Jerry Anning)

Basically, you have a ray going "between the cracks" of the height field due to an arithmetic accuracy problem. Sometimes it does no harm. Sometime you get black dot or line artifacts. I know of no successful patch so far. I also know no completely reliable workaround. The best bet is to slightly joggle the camera position and/or angle.