Add PDF reports while using split-merge

[pierotofy]

Currently ODM does not generate PDF reports when using split-merge. It could be possible to generate them by:

• Recomputing/aggregating stats from submodels
• Write a new report generation code (separate from OpenSfM's)

[smathermather]

I'd lean toward aggregate stats. Any reason to not have submodel stats as well? For larger datasets it could be more useful than global stats.

[pierotofy]

I agree to both. The bottom line is that the split-merge report would contain slightly different information compared to normal runs.

[smathermather]

Yup. Agreed.

[YanNoun]

@pierotofy opensfm/action/compute_statistics.py calls stats.py functions that works on a list of reconstructions.

[pierotofy]

Didn't know that. Thanks @YanNoun ! I'll try it out.

[YanNoun]

The save_heatmap/save_topview might be super slow with 100K/1M points, feel free to run some random index-based decimation.

[pierotofy]

I did notice some slowdowns with larger datasets; would this be a good idea for a PR to OpenSfM for the compute_statistics command? (I could add a --decimate flag)

[YanNoun]

Yup definitely, that would be great !

[pierotofy]

mapillary/OpenSfM#695

I opted to allow a user to set a cap on the number of points using random sampling. Definitely helps keep runtime in check!