Stitching vertices to no-data pixels create walls

ℹ️ Funded by an industrial customer.

Summary

For map tiles, the stitching algorithm "stitches" the edges between two neighbouring tiles, in order to avoid small gaps. However, if the neighbouring tile is 100% made of no-data value, then the computed height for the edge will be zero, which in some cases can produce a huge difference in height, defeating the purpose of the stitching algorithm.

Normally, this wouldn't be an issue as those walls are eliminated by the transparent pixels. However, in some rare cases, such as when the no-data boundary is very close to the neighbour tile, the wall can be seen.

Steps to reproduce

1. Open the cog_nodata example
2. Set the "replace no data pixels with" to "opaque alpha"
3. Move the camera to a region with no-data, and zoom until a map tile becomes 100% no-data.

Expected behaviour:

The no-data tile should be ignored for the purpose of stitching.

Actual behaviour:

The tiles that are neighbours to the no-data tile have vertical walls on their shared edge with the no-data tile.

Informations

• Giro3D version: 0.29
• Browser (Firefox, Chrome, Opera, Safari...) and version: N/A
• OS (Linux, MacOS, Windows...) N/A

Screenshots