# Warping and Partitioning for Low Error Shadow Maps

## Addendum

When we compute the storage factor in the paper for the light behind the viewer, we ignore the near plane. This makes little difference when the depth ratio *(f/n)* is large. But after repeated *z*-partitioning, the depth ratio becomes much smaller and the near plane becomes significant. Figure 12 in the paper should actually look like this:

Note that for the light behind the viewer, the storage factor for *z*-partitioning with and without warping (ZP and ZP+W) initially decreases, but then begins to slowly grow. This is due to the fact that from this light direction there is significant overlap between the shadow maps.

There is a point at which face partitioning (FP+ZP+W) actually becomes better than *z*-partitioning. This figure shows where that crossover occurs for varying parameters:

Each region is labelled with the lowest error algorithm. Since we are looking for an algorithm that performs well at high depth ranges with just a few shadow maps, our recommendation to use z-partitioning with warping (ZP+W) does not change.

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