Processor: Allow client to specify progress callback function

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.56716% with 18 lines in your changes missing coverage. Please review.

Project coverage is 90.73%. Comparing base (5cfeff2) to head (6b4dde4). Report is 3 commits behind head on master.

Files	Patch %	Lines
python/src/exactextract/exact_extract.py	55.00%	9 Missing :warning:
src/utils_cli.cpp	0.00%	3 Missing :warning:
src/feature_sequential_processor.cpp	89.47%	2 Missing :warning:
src/processor.h	77.77%	2 Missing :warning:
python/src/exactextract/feature.py	87.50%	1 Missing :warning:
src/exactextract.cpp	50.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #128 +/- ## ========================================== + Coverage 90.52% 90.73% +0.20% ========================================== Files 85 85 Lines 6082 6176 +94 Branches 611 611 ========================================== + Hits 5506 5604 +98 + Misses 544 540 -4 Partials 32 32 ```

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[JakubCha]

Hello Dan. I don't know if it's the correct place to ask. I can move it to issues if preferred. Do you plan to expose this functionality to Python API? I'd make use of this in the QGIS plugin as right now I have no way of reporting to user progress of calculating stats.

[dbaston]

Yes, I would expose it to Python. I am wondering if I should also extend it to directly provide a progress percentage.

[JakubCha]

It would be nice to have that as well. I wonder how it would work in Python API.

• in the case of feature-sequential it would make a call to callback function every time the feature is calculated
• raster-sequential - make callback for each chunk is calculated

Am I thinking about it correctly?

[dbaston]

@JakubCha Currently yes, the progress callback is invoked either once per feature or once per raster chunk. In the per-chunk case, the caller has no simple way to know how many chunks there will be, so I've updated the progress bar to take two arguments: the fraction completed, and an informational message. This would also allow providing more frequent progress updates when a feature needs to subdivided to limit memory usage, or when a raster chunk has many intersecting features.