Image Orientation

Images can be created in two frames of reference, earth and sun-earth. Ground-based imagers normally use the earth frame of reference. Satellite images, and ground-based instruments very close to the geographic poles, use the sun-earth frame of reference.

Earth frame of reference

The frame of reference is fixed to the Earth. For thumbnails four possible orientations are permitted: North at top, looking down (ie East right); North at top, looking up (ie East left); South at top, looking down (ie East left); South at top, looking up (ie East right). Images can be selected in any possible orientation, with 4 extra options added for inter-hemispherical studies (Pole at top, looking down; Pole at top, looking up; Equatorward at top looking down; Equatorward at top, looking up). The descriptions use looking up/down because in the Poleward and Equatorward options the position of East depends on the hemisphere in which the instrument is located.

Keograms can be orientated with either North or South at the top, and must match that chosen for thumbnails. The left edge of the keogram is always the start of the UT day and the right edge the end of the UT day.

Sun-Earth frame of reference

The frame of reference is fixed to the Sun-Earth line. The top of the image always point sunwards. Two possible orientations are permitted: North pole view (dawn on the right and dusk on the left) and South pole view (dawn on the left and dusk on the right).

Keograms are taken at a fixed magnetic local time. The top of the keogram represents the poleward edge (eg 5° or 90° latitude), and the bottom of the keogram represents the equatorward edge (eg 55° latitude). There are no orientation options for keograms in the Sun-Earth frame of reference.

Topic revision: r2 - 2007-03-29 - 18:24:20 - SteveMarple
 
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