ease_lonlat

Small package to convert given geographic coordinates (longitude, latitude) to EASE(2)-grid coordinates (col, row) and vice versa.

This code is inspired by the 'easeconv-0.3' software, the EASE-Grid map transformation utilities Developed and distributed by the National Snow & Ice Data Center (NSIDC), University of Colorado at Boulder. But instead of defining projections and grids "from a scratch", the pyproj library and definition of grids from NSIDC have been used.

MOTIVATION

Get SMOS (CATDS, 25km, global projection) row and col coordinates corresponding to the pixel of EASE2 grid with given lon-lat coordinates.

SUPPORTED GRIDS

'N' stands for North Polar (Lambert's equal-area, azimuthal), 'S' for South Polar (Lambert's equal-area, azimuthal) and 'G' for Global (cylindrical, equal-area) projection. 3125km means pixel size of 3.125 km, 625 means 6.25 km and 125 means 12.5 km.

• EASE2_G1km
• EASE2_G3km, EASE2_N3km, EASE2_S3km
• EASE2_G3125km, EASE2_N3125km, EASE2_S3125km
• EASE2_G625km, EASE2_N625km, EASE2_S625km
• EASE2_G9km, EASE2_N9km, EASE2_S9km
• EASE2_G125km, EASE2_N125km, EASE2_S125km
• EASE_G125km, EASE_N125km, EASE_S125km
• EASE2_G25km, EASE2_N25km, EASE2_S25km
• EASE_G25km, EASE_N25km, EASE_S25km
• EASE2_G36km, EASE2_N36km, EASE2_S36km

TESTED GRIDS

Tested on SMAP data. EASE2-grids - 9km (N, S, G), 36km (N, G).

NOT TESTED GRIDS

If you can test this code on some of the not tested grids, I would appreciate if you do it and let me know :) Especially EASE grids.

• EASE-grids - all.
• EASE2-grids - 1km, 3km, 3.125km, 6.25km and 25km

USAGE

from ease_lonlat import EASE2GRID, SUPPORTED_GRIDS

# define new grid by yourself
grid = EASE2GRID(name='EASE2_G36km', epsg=6933, x_min=-17367530.45, y_max=7314540.83, res=36032.22, n_cols=964, n_rows=406)

# or using parameters taken from NSIDC and kept in SUPPORTED_GRIDS
grid = EASE2GRID(name='EASE2_G36km', **SUPPORTED_GRIDS['EASE2_G36km'])

# convert longitude and latitude to row and col indices
point_lon = 17.4
point_lat = 49.4

# row should be 48, col should be 528
col, row = grid.lonlat2rc(lon=point_lon, lat=point_lat)

# get lon, lat of the center of the pixel
pixel_center_lon, pixel_center_lat = grid.rc2lonlat(col=col, row=row)

TODO

• Generate grid for given region (by lat/lon min/max)
• Add documentation