Possible to remap from grid to swath?

[pytroll]

Possible to remap from grid to swath?

[mraspaud]

From jakob.malm on May 19, 2010 10:25:19

Would grid.get_image_from_lonlats do this? I tried the code below, but my area_def
may be completely wrong. I have a rotated lon/lat NWP field, tsur, obtained using
pygrib. The grid is defined in the GRIB file by the following:

first grid point (lon: -22.6°, lat: -31.0°)
last grid point (lon: 38.4°, lat: 30.0°)
southern pole (lon: -10°, lat: -30°)
angle of rotation: 0°

In mind, the following python code should return an array with values very similar to
tsur.values, because tsur.latlons() fills the grid. Instead, the values have a much
reduced range.

area_def = pyresample.utils.get_area_def('hirl', 'HIRLAM NWP area', 'rotated_ll',
'+proj=ob_tran +o_proj=longlat +lon_0=-10 +o_lat_p=-30', 306, 306, (-23, -31, 38, 30))
lons = tsur.latlons()[1]
lats = tsur.latlons()[0]
tsur_resampled = pyresample.grid.get_image_from_lonlats(lons, lats, area_def,
tsur.values)

Another, even simpler, test, which should also return the same values:

tsur_resampled = pyresample.grid.get_resampled_image(area_def, area_def, tsur.values)

Instead of the same values, the resulting array is built of many tiles, and the value
range is much reduced in this case too.

Is it perhaps not possible to use rotated lon/lat projections with these functions?

[mraspaud]

From [email protected] on June 01, 2010 12:57:16

[The answer here is purely informative since we solved the problem together with Jakob.]

In your case, you should use pyresample.swath.resample_* instead:

You have the input lons and lats, and the target lons and lats, so for example:
result_array = pyresample.swath.resample_nearest(lons.ravel(), lats.ravel(),
mydata.ravel(), target_area_def, 5e4)
where target_area_def is a stack of both lons and lats.

Martin

[mraspaud]

From [email protected] on June 21, 2010 01:05:34

The API has changed in 0.6.0 in order to make this use-case more transparent. Please refer to the documentation.

Status: Fixed