[gdal-dev] Creating Cloud Optimized GeoTIFFs

[anash]

Hi Even,

I have seen pretty much everywhere that COG's are created in 3 steps:

1. compress and tile the image

$ gdal_translate -co TILED=YES -co COMPRESS=DEFLATE in.tif tmp.tif

2. add overviews

$ gdaladdo -r average 2 4 8 16 tmp.tif

3. reorder overviews

$ gdal_translate -co TILED=YES -co COMPRESS=DEFLATE -co
COPY_SRC_OVERVIEWS=YES tmp.tif out.tif

However, it seems that we're tiling and compressing with gdal_translate
twice, which doesn't seem to be the most efficient way to do things.

I have run some initial tests on an untiled/uncompressed image basically
skipping step 1 and going straight to adding overviews and translating to
reorder, compress, and tile. The resulting image passes the COG validator
test, meaning it is a "valid" COG, though the overview offset values are
slightly different:

>>> validate(gdal.Open('tile_first_cog.tif'))
... ([], {'ifd_offsets': {'main': 8, 'overview_2': 31886, 'overview_3':
32822, 'overview_0': 18238, 'overview_1': 28966}, 'data_offsets': {'main':
180166631, 'overview_2': 2300609, 'overview_3': 33246, 'overview_0':
45588773, 'overview_1': 11129028}})

>>> validate(gdal.Open('no_init_tile_cog.tif'))
... ([], {'ifd_offsets': {'main': 8, 'overview_2': 31138, 'overview_3':
32074, 'overview_0': 17490, 'overview_1': 28218}, 'data_offsets': {'main':
180165883, 'overview_2': 2299861, 'overview_3': 32498, 'overview_0':
45588025, 'overview_1': 11128280}})

I am wondering, is there any downside to not starting with an initial
tiling/compression? 



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