Andrew G

Well, re the test case using an artificial raster I did look at doing that, and also a C test aka lib/raster3d. The first was a bit far from the...

@marisn yes, re q1 != 0.0, that's exactly right, it just guards against when q1 really is exactly 0.0 + I'll try and find some time to write the test...

I've added a unit test that covers a range of horizons and uses the North Carolina test location.

Ok, so the tests I wrote fail when run from the CI system and I don't know why. I'm running them from the grass cli with the current mapset set...