Creating annotated orthomosaic fails when orthomosaic is too big

[jreyesr]

This issue is linked to https://github.com/IS-AgroSmart/AgroSmart-Web/issues/100, but it's not the same.

When the original orthomosaic is too big (tested on a 1.1GB orthomosaic), the Django server crashes when creating the annotated orthomosaic (the one with the snapshot locations). Probably due to lack of memory or some obscure bug in Matplotlib/Pillow/Numpy/whatever.

Suggested fix: creating a smaller version of the orthomosaic (say, 1080px high and whatever width is required to match), call it odm_orthophoto_small.png and using that version to create the annotation. That code may be quite similar to the try_create_thumbnail method, only that the size will be different.

• [ ] Refactor the thumbnail creation code into a private method _create_png_orthomosaic(self, height, out_name) that invokes the command f"gdal_translate -of PNG -outsize 0 {height} {self.get_disk_path()}/odm_orthophoto/rgb.tif {out_name}"
• [ ] Refactor try_create_thumbnail to call _create_png_orthomosaic(512, self.get_thumbnail_path())
• [ ] Add new method on Flight model: get_small_path(self) with content return self.get_disk_path() + "/odm_orthophoto/odm_orthophoto_small.png"
• [ ] Add new line at the start of try_create_annotated_png_ortho: _create_png_orthomosaic(1080, self.get_small_path())
• [ ] Change line im = plt.imread(self.get_png_ortho_path()) on try_create_annotated_png_ortho to instead be im = plt.imread(self.get_small_path())

[jreyesr]

Expected result: a file odm_orthophoto_small.png will be created on flights/uuid/odm_orthophoto. The file will have a 1080px (or thereabouts?) vertical resolution. Since the file will be smaller (and, more importantly, its size will be constant even if the input orthomosaic is huge) the annotated orthomosaic creation will succeed. The annotated orthomosaic will obviously have a 1080px vertical res too, but it is only used on the report, so it should be Good Enough (TM) to be rendered on a PDF.