Interpreting bounding box in gis

Question

I am trying to understand geo static analysis

test_img_msk = "http://oin-hotosm.s3.amazonaws.com/5a95f32c2553e6000ce5ad2e/0/10edab38-1bdd-4c06-b83d-6e10ac532b7d.tif"

test_img_msk_rast = rasterio.open(test_img_msk)
print('test imag mask bounds ', test_img_msk_rast.bounds)

from rio_tiler.io import COGReader
with COGReader(test_img_msk) as cog:
    print(cog.info())

Above code output is shown below

output 1: test imag mask bounds  BoundingBox(left=683715.3266400001, bottom=1718548.5702, right=684593.2680000002, top=1719064.90736)

output 2: bounds=BoundingBox(left=-61.287001876638215, bottom=15.537756794450583,
                   right=-61.27877967704677, top=15.542486503997608)
                  center=(-61.28289077684249, 15.540121649224096, 16)
                  minzoom=16 maxzoom=22
                  band_metadata=[('1', {}), ('2', {}), ('3', {})]
                  band_descriptions=[('1', ''), ('2', ''), ('3', '')]
                  dtype='uint8' nodata_type='None'
                  colorinterp=['red', 'green', 'blue'] 
                  scale=None offset=None colormap=None 
                  overviews=[2, 4, 8, 16, 32, 64] 
                  count=3 height=11666 width=19836 driver='GTiff'

My question is what is relation between bounding box left=683715.3266400001 and left=-61.287001876638215 in output 2. How to interpert this? Kindly help

Answer 1

Your dataset test_img_msk has a projected coordinate system, EPSG:32620 to be specific which uses coordinate units of meters.

The second bounding box seems to be in a different coordinate system, likely a geographic coordinate system, where the coordinate units are decimal degrees.

So in the end, your left boundary is the same location, just in a different coordinate system.

For more info on projected vs geographic coordinate system, check this article .

Edit :

Looking at the source code of COGReader.info reveals that the bounding box coordinates are transformed from the native projection to the GCS WGS84 using transform_bounds .