Change compression predictor for DEMs to 3

[pierotofy]

PREDICTOR=[1​/​2​/​3]: Defaults to 1. Set the predictor for LZW, DEFLATE and ZSTD compression. The default is 1 (no predictor), 2 is horizontal differencing and 3 is floating point prediction. PREDICTOR=2 is only supported for 8, 16, 32 and 64 bit samples. PREDICTOR=3 is only supported for 16, 32 and 64 bit floating-point data.

[andrewharvey]

For context, I noticed this while doing a broad investigation on how we could reduce asset space of disk at https://discord.com/channels/1490218202033029212/1490219150222688487/1514265197366481096

Since the DEMs use Float32, PREDICTOR=3 can offer some benefits. In my test my dsm.tif only reduced from 104MB to 103MB not not much difference, but my dtm.tiff went from 113MB to 101MB, which is worth the change as it doesn't seem to make much difference speed wise.

It would be a good idea to do more real world benchmarking though, and compare this when run at the same step as the DTM/DSM creation, rather than post-processing the built dtm/dsm.

[andrewharvey]

It looks like this was also discussed in WebODM/WebODM#1099 and @Saijin-Naib made some suggestions.

From my further testing it appears -of COG with -co PREDICTOR 3 -co LEVEL=12 provides the smallest file size, bringing my original dtm.tif from 113MB to 97MB.

the LEVEL=12 is slower though.

[pierotofy]

Some more benchmarks https://kokoalberti.com/articles/geotiff-compression-optimization-guide/