Troubleshooting automatically generated lightmap UVs

Pack Margin

To allow filtering, the lightmap contains lighting information in texels near the chart border, so always include some margin between charts to avoid light bleeding when applying the lightmap.

The lightmap resolution defines the texel resolution of your lightmaps. Lightmappers dilate some chart texels in the lightmap to avoid black edges, so the UV charts of your Mesh need to be at least two full texels apart from each other to avoid light bleeding. Use the Pack Margin setting to ensure you have enough margin between the UV charts of your geometry.

In lightmap UV space, the padding between charts need to be at least two full texels in order to avoid UV overlapping and accidental light bleeding. In this image, the black space represents the space between charts.

Min Lightmap Resolution and Min Object Scale

Placing UV charts too close together may cause cross-chart texel bleeding in the final lightmap. Placing charts too far away from each other wastes memory. The ideal packing margin of an object depends on how many lightmap texels are allotted to it.

The number of texels that Unity uses for a MeshRenderer depends on the MeshRenderer’s lightmap resolution and transform scale. To calculate a good margin, Unity needs to know the expected minimum values for these properties.

A MeshRenderer’s lightmap resolution is a combination of the Lightmap Resolution property of the Lighting Settings Asset for the Scene that the MeshRenderer appears in, and the Scale in Lightmap property of the MeshRenderer. Note that this means that the same MeshRenderer can have a different lightmap resolution in different Scenes.

You can use the Inspector to view the lightmap resolution of a MeshRenderer in a given Scene:

1. In the Scene view or Hierarchy, select the GameObject that has the MeshRenderer component.
2. In the Inspector, navigate to the MeshRenderer component’s Lightmapping section.
3. Open the Baked Lightmap fold-out. Unity displays the MeshRenderer’s lightmap resolution in the baked lightmap with the label Lightmap Resolution, and its transform scale in the baked lightmap with the label Lightmap Object Scale.

Angle distortion

The following screenshots demonstrate equal resolution, but with different UVs. The first image has a high Angle Error, and the result contains unintended artifacts. The second image has the default Angle Error (8%). In Meshes with more triangles, angle distortion can significantly distort the shape.

Area distortion

In the image below, two spot lights with the same parameters light the sides of a cylinder. The right-hand side of the cylinder has a higher Area Error value, which distorts the triangles and leads to a lower resolution, creating artifacts in the light.