when using the unity terrain and determining a point on the terrain via raycast, I want to get a collection of terrain points that are within a sphere with the raycast point as the center.

Now, to get all the points within a vertical cylinder is easy: Just return all the points that are within a circle in the flat 2d heightmap.

However, this is not the same as comparing a sphere, see the attached image (black is the terrain, e.g., one steep peak, red is the sphere, blue is the cylinder, the striped areas are the parts of the terrain that are marked by the geometric shape). In this example, the cylinder would mark a lot more points than the sphere.

I realise that I can initially grab all the points within the cylinder and then sample the heights and compare their distance to the center of the sphere and exclude them if the distance is greater than the radius.

But I would like to know if I am missing a more efficient method here, like some inbuilt function I overlooked or use a vertex shader.

Thanks for your input

ps: I think you cannot access the vertex information of a terrain directly: here or here

They already said that they understood they COULD use the technique you described. You also should use the code tags to properly format your code so itâ€™s readable.

@FinTerra , if you have to iterate through all the points, you can at least check if itâ€™s inside the AABB of the sphere before calculating the distance. For a SphereCollider, this can be done with a colliderâ€™s .bounds which is already calculated for you. Otherwise, check if the Mathf.Abs(xTerrainPoint - xSphereCenter) > sphereRadius then also check Y, then also check Z, and only calculate the distance if youâ€™re within all of those box dimensions.

I apologize if Iâ€™m wrong but Thintedâ€™s post is probably a ChatGPT suggestion. There shouldnâ€™t be any need for spatial partitioning as the GetHeights function will take the points of interest directly from the specified region of the height map. Thereâ€™s no searching required.

Youâ€™re right that it can help but youâ€™re still going to want to do some calculations. GetHeights() is integer sample based, not world coordinate based. You should figure out what span of integer samples are within the world span of X and Z of interest. You can then still check the Y heights against the Y axis bounds of the sphere in question before you check if a hill or valley happens to poke into the sphere or not.