User's Guide

GETREGIONS

Determine which regions lie within an image

Function:

Determine which of the 12 regions of the global Goode's projection lie within an image.

Parameters:

IN
Input image. The AVHRR archive image for which regions are to be determined. Window and band specifications are not allowed.

NLINES(100)
Number of lines. The number of lines to skip between points of evaluation. The smaller this number is, the less likely it is for a region within the boundaries of the image to be missed.

REGIONS
Regions in image. The region numbers (1 - 12) of the global Goode's projection that fall within the image will be returned as a list in the specified TAE string variable. This variable must have been previously defined. The area extents of these 12 regions are defined in User Note 1.

Example:

  1. LAS> getregions in=ah11041292190004 nlines=10 regions=regstr

    GETREGIONS determines which of the 12 regions lie within the AVHRR archive image AH11041292190004 and returns them in REGSTR. For instance, the return value of REGSTR might be "1 3" indicating that regions 1 and 3 lie within the image.

Description/Algorithm:

To determine the regions that lie within an image, GETREGIONS selects pixels at every NLINES'th line, starting at line 1, along the left and right sides and along the nadir track (center pixel) of the AVHRR archive image. For each selected pixel, the line / sample location is converted to a latitude / longitude location and is evaluated to determine which region the point lies within. All of the region numbers that intersect the bounds of the image are returned to TAE.

Nonfatal Error Message:

    None.

Fatal Error Messages:

  1. [getregions-fatal] Fatal error encountered

    A fatal error was encountered. The message preceding this message is the specific error encountered.

  2. [getregions-dtae] Error sending variable to TAE

    An error was encountered attempting to send the REGIONS variable to TAE. Verify that the variable has been declared as a TAE string.

User Notes:

  1. The boundaries for the 12 regions of the world are defined as follows:

    Region     Minimum      Maximum      Minimum      Maximum
    number     latitude     latitude     longitude    longitude
               (degrees)    (degrees)    (degrees)    (degrees)
    ------------------------------------------------------------
    1          40.73333      90.0         -180.0       -40.0
    2          40.73333      90.0          -40.0       180.0
    3           0.0          40.73333     -180.0       -40.0
    4           0.0          40.73333      -40.0       180.0
    5         -40.73333       0.0         -180.0      -100.0
    6         -40.73333       0.0         -100.0       -20.0
    7         -40.73333       0.0          -20.0        80.0
    8         -40.73333       0.0           80.0       180.0
    9         -90.0         -40.73333     -180.0      -100.0
    10        -90.0         -40.73333     -100.0       -20.0
    11        -90.0         -40.73333      -20.0        80.0
    12        -90.0         -40.73333       80.0       180.0
    

  2. The region numbers that lie within the bounds of the image will be returned in a TAE variable that must be declared prior to calling GETREGIONS. For example, if REGIONS=regns, the following declaration must have previously been made while in LAS:

           local regns type=string