wiki:proj=geos

GEOS

The geos projection pictures how a geostationary satellite scans the earth at regular scanning angle intervals.

In order to project using the geos projection you can do the following:

proj +proj=geos +h=35785831.0

The required argument h is the viewing point (satellite position) height above the earth.

Other arguments include:

  • lon_0: the subsatellite longitude point
  • sweep: the sweep angle axis of the viewing instrument. Can be x or y (y is the default). (new in 4.8.0)

The projection coordinate relate to the scanning angle by the following simple relation:

scanning_angle (radians) = projection_coordinate / h

Note on sweep

The viewing instrument on-board geostationary satellites described by this projection have a two-axis gimbal viewing geometry. This means that the different scanning positions are obtained by rotating the gimbal along a N/S axis (or y) and a E/W axis (or x).

https://upload.wikimedia.org/wikipedia/commons/1/19/Two-axis_gimbal.svg

In the image above, the outer-gimbal axis, or sweep-angle axis, is the N/S axis (y) while the inner-gimbal axis, or fixed-angle axis, is the E/W axis (x).

This example represents the scanning geometry of the Meteosat series satellite. However, the GOES satellite series use the opposite scanning geometry, with the E/W axis (x) as the sweep-angle axis, and the N/S (y) as the fixed-angle axis.

The sweep argument is used to tell proj.4 which on which axis the outer-gimbal is rotating. The possible values are x or y, y being the default. Thus, the scanning geometry of the Meteosat series satellite should take sweep as x, and GOES should take sweep as y.

Last modified 10 months ago Last modified on Feb 18, 2016 12:11:30 PM

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