User's Guide

SETLUT

Find the look-up table (mapping values) for a facsimile print

Function:

Find the look-up table (mapping values) to be used for a facsimile print based on a specified solar zenith view angle.

Parameters:

SUNZEN
Sun zenith angle. The angle from 90 degrees that the path of incident solar energy strikes the earth. The sun zenith angle is calculated at the center of an image and is specified in total degrees.

LUTNUM
Look-up table number. The number of the look-up table which is selected based on the sun zenith angle. This number is returned in the specified TAE variable.

FROM
Input mapping values. The input mapping values which are selected based on the sun zenith angle. The selected input mapping values are returned in the specified TAE variable.

TO
Output mapping values. The output mapping values which are selected based on the sun zenith angle. The selected output mapping values are returned in the specified TAE variable.

NBITS(10)
Number of bits. Select a look-up table for 8 bit or 10 bit data.

  =  8:  8 bit data.  The data
         ranges from 0 to 255.

  = 10:  10 bit data.  The data
         ranges from 0 to 1023.

Examples:

  1. LAS> setlut sunzen=48.154 lutnum=lnum from=fmap to=tmap

    The 10 bit input and output mapping values for a sun zenith angle between 40 and 50 degrees are selected and returned in the TAE variables FMAP and TMAP. The selected look-up table number is also returned in the TAE variable LNUM.

  2. LAS> setlut sunzen=98.273 lutnum=lnum from=fmap to=tmap nbits="8"

    The eight bit input and output mapping values for a sun zenith angle greater than 90 degrees (night) are selected and returned in the TAE variables FMAP and TMAP. The selected look-up table number is also returned in the TAE variable LNUM.

Description/Algorithm:

A look-up table containing mapping values is defined for each 10 degrees of the sun's zenith angles (0 to 90 degrees). Based on the sun's zenith angle and number of bits, the appropriate input and output mapping values are selected and returned to the calling routine though the TAE name variables specified in FROM and TO. The selected look-up table number is also returned to the calling routine through the TAE name variable specified in LUTNUM. For sun zenith angles that are less than zero or greater than ninety, a look-up table number used for night data will be returned.

Nonfatal Error Messages:

    None.

Fatal Error Messages:

    None.

User Notes:

  1. Sun zenith angles range from zero to ninety degrees; any angles less than zero or greater than ninety occur at night. In these cases, the look-up table number for night data is returned.

  2. The sun zenith angle is calculated at the center of the image and is specified in total degrees.