satpy.readers._geos_area module

Geostationary Projection / Area computations.

This module computes properties and area definitions for geostationary satellites. It is designed to be a common module that can be called by all geostationary satellite readers and uses commonly-included parameters such as the CFAC/LFAC values, satellite position, etc, to compute the correct area definition.

satpy.readers._geos_area.get_area_definition(pdict, a_ext)

Get the area definition for a geo-sat.

Parameters:

• pdict – A dictionary containing common parameters: nlines: Number of lines in image ncols: Number of columns in image ssp_lon: Subsatellite point longitude (deg) a: Earth equatorial radius (m) b: Earth polar radius (m) h: Platform height (m) a_name: Area name a_desc: Area description p_id: Projection id

• a_ext – A four element tuple containing the area extent (scan angle) for the scene in radians

Returns:

An area definition for the scene

Return type:

a_def

Note

The AreaDefinition proj_id attribute is being deprecated.

satpy.readers._geos_area.get_area_extent(pdict)

Get the area extent seen by a geostationary satellite.

Parameters:

pdict – A dictionary containing common parameters: nlines: Number of lines in image ncols: Number of columns in image cfac: Column scaling factor lfac: Line scaling factor coff: Column offset factor loff: Line offset factor scandir: ‘N2S’ for standard (N->S), ‘S2N’ for inverse (S->N) h: Altitude of satellite above the Earth’s surface (m)

Returns:

An area extent for the scene

Return type:

aex

satpy.readers._geos_area.get_geos_area_naming(input_dict)

Get a dictionary containing formatted AreaDefinition naming.

Parameters:

input_dict – dict Dictionary with keys platform_name, instrument_name, service_name, service_desc, resolution . The resolution is expected in meters.

Returns:

area_naming_dict with area_id, description keys, values are strings.

Note

The AreaDefinition proj_id attribute is being deprecated and is therefore not formatted here. An empty string is to be used until the attribute is fully removed.

satpy.readers._geos_area.get_resolution_and_unit_strings(resolution)

Get the resolution value and unit as strings.

If the resolution is larger than 1000 m, use kilometer as unit. If lower, use meter.

Parameters:

resolution – scalar Resolution in meters.

Returns:

Dictionary with value and unit keys, values are strings.

satpy.readers._geos_area.get_xy_from_linecol(line, col, offsets, factors)

Get the intermediate coordinates from line & col.

Intermediate coordinates are actually the instruments scanning angles.

satpy.readers._geos_area.make_ext(ll_x, ur_x, ll_y, ur_y, h)

Create the area extent from computed ll and ur.

Parameters:

• ll_x – The lower left x coordinate (m)

• ur_x – The upper right x coordinate (m)

• ll_y – The lower left y coordinate (m)

• ur_y – The upper right y coordinate (m)

• h – The satellite altitude above the Earth’s surface

Returns:

An area extent for the scene

Return type:

aex

satpy.readers._geos_area.sampling_to_lfac_cfac(sampling)

Convert angular sampling to line/column scaling factor (aka LFAC/CFAC).

Reference: MSG Ground Segment LRIT HRIT Mission Specific Implementation, Appendix E.2.

Parameters:

sampling – float Angular sampling (rad)

Returns:

Line/column scaling factor (deg-1)