Exporting netcdf file in MODIS sinusoidal grid with xarray

Question

I have 18 tif files in the MODIS sinusoidal grid I would like to convert to one file in netcdf format. I have converted the tifs to an xarray xarray.core.dataset.Dataset format called stacked. At this point if my projection is WGS 84 I can usually export to netcdf like so:

stacked.lat.attrs['long_name'] = 'latitude'
stacked.lat.attrs['units'] = 'degrees_north'
stacked.lat.attrs['standard_name'] = 'latitude'
   
stacked.long.attrs['long_name'] = 'longitude'
stacked.long.attrs['units'] = 'degrees_east'
stacked.long.attrs['standard_name'] = 'longitude'
   
    
stacked[variable].attrs['coordinates'] = 'time lat long'

but since MODIS is not in degrees this causes a problem. I tried to change the units to 'meters' but that did not work. Is there a way to export to netcdf with MODIS (https://spatialreference.org/ref/sr-org/modis-sinusoidal-3/) instead of WGS 84?

cyril · Accepted Answer · 2021-09-06 09:11:31Z

1

Refering to https://spatialreference.org/ref/sr-org/modis-sinusoidal-3/, I am able to define crs using the proj4 standard. Then, I use rioxarray to georeference the dataset. Assuming your dimensions-coordinates are y and x, I would write :

import rioxarray

crs = "+proj=sinu +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"

stacked = stacked.rio.set_spatial_dims(x_dim="x", y_dim="y").rio.write_grid_mapping().rio.write_crs(crs).rio.write_coordinate_system()

A spatial_ref coordinate is created, and the units of your coordinates are normally correct now.

Tell me if it doesn't fit exactly your question.

edited Sep 6, 2021 at 9:11

answered Sep 6, 2021 at 9:05

cyril

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