Terrain Grass Detail Texture Atlas

Hello,

Is there a way to get access to the texture atlas of terrain details (grass textures) ?

I already figured out that I can access every detail texture separately by terrain.terrainData.detailPrototypes[index].prototypeTexture,

but I want to know the Rects on the texture atlas that is send by the terrain to the shader.

I tried to make my own Texture Atlas using Texture2D.PackTextures method but textures are layout different than in the original texture atlas.

T$$anonymous$$s is how looks detail texture atlas made by Unity Terrain:

And t$$anonymous$$s is how looks texture atlas made by me using Texture2D.PackTextures:

As you can see t$$anonymous$$s does not line up (I care about the sizes not the color).

There is the script I wrote to generate the Texture Atlas:

 DetailPrototype[] prototypes = terrain.terrainData.detailPrototypes;
 Texture2D atlas = new Texture2D(terrain.terrainData.detailWidth,
                                 terrain.terrainData.detailHeight);
 Texture2D[] atlasTextures = prototypes.ToList().Select(x => 
                             new Texture2D(x.prototypeTexture.width, x.prototypeTexture.height)
                             ).ToArray();
 Rect[] rects = atlas.PackTextures(atlasTextures, 1, terrain.terrainData.detailWidth);