Reproducing Terrain.SampleHeight() for custom mesh terrains

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Hi folks! I'm trying to write a method which mimics GetHeights() or SampleHeight(), but which works on my own generated mesh terrains. They're functionally similar, just subdivided planes. Each vertex's y position is set by a float[,] heightmap, just like built-in terrains.

I'm finding that similar issues are a common rite-of-passage thing, but I get the feeling I'm missing some simple algorithm that would be lightning fast given that this is a very specific case. It'd be so easy to sample these points using raycasting, but I'm hoping for a less expensive solution based on some mesh-level math wizardry. Am I wrong in assuming this is wise?

For bonus points, could my solution to this also provide a foundation for reproducing GetSteepness() or GetInterpolatedNormal()? Will post again if I have any success on my own. Thanks for any ideas / insight!

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Answer by AlwaysSunny · Jun 05, 2013 at 04:59 AM

I can easily find and reference the nearest vertex because the data structure I use allows this to be really cheap. Since the necessary projections are all XZ parallel, based on which direction I rounded to arrive at the nearest vertex, I can discover the quad the target position is in pretty darn quick and cheap.

Doing some "fancy collegiate arithmetic" picks the correct three points describing the tri and does a weighted interpolation for a height value.

This approach applies to a float[,] heightmap data set, but would also be useful - if slightly more expensive - when working with mesh.vertices in similar cases.

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MattMcg.GameDev · Jan 28, 2015 at 10:39 AM 0

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Hey, I know you posted this a while ago but I was wondering if you still had the code for this? I would really appreciate the help figuring this out for my custom terrain. I do not want your code directly, just some help.

I know how to find the exact 4 height points at a given location. I then struggle to work out which tri I need, i.e. the "fancy collegiate arithmetic". Even if I had the tri, I also don't know what to do with the 3 points I end up with, i.e. how to interpolate it. $$anonymous$$ath is not my strong point.

AlwaysSunny · Jan 28, 2015 at 11:24 AM 1

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I gave a good try hunting this old script but my archives are a nightmare.

The code wasn't complex IIRC. If you know your mesh and the winding order for each quad's tris, finding which tri is your test candidate is as easy as comparing which tri's "90-degree" vertex is closer to the position argument.

e.g. which is closer, the vert at quad[0] (use tri 0,1,3) or the vert at quad[2] (use tri 2,3,1)

From there I'm fuzzy on what I did to sample the height, but it wasn't hard to find the formula once I chose good search terms. Gotta leave that part to you. ;)

$$anonymous$$eep in $$anonymous$$d it's not necessarily prudent to do this. Raycasting may be a superior choice, it all depends on your situation.

Best of luck,

MattMcg.GameDev · Jan 28, 2015 at 11:29 AM 0

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Oh wow. That is such a simple way to figure out with which tri it lies on... I was imagining being far more difficult!

I have tried with Raycasts and it seems a little too expensive for me, due to the amount of objects and terrain sectors. I'm even contemplating using a collider-less terrain as I don't actually need realistic physics. I might just make a very simple custom physics that uses this height sampler to detect when it's on the ground.

Thank you for your reply, you've given me enough direction to solve this I think.

Reproducing Terrain.SampleHeight() for custom mesh terrains

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