User's Guide

AVHRRCHIPS

Create AVHRR image chips.

Function:

Create image chips in AVHRR satellite space from a single base image and a set of tie points in a TPS file.

Parameters:

IN
Input images. The first image is the base image from which chips will be taken. It must be a single-band image. The second image is the AVHRR image whose space will be used to warp the chips.

INTS
Input tie point selection file. This file specifies tie points, whose latitude and longitude coordinates become the center of each chip.

OUTMT
Output merged tie point file. A merged tie point file contains coordinates in the reference (chip) and search images corresponding to each tie point, along with other information that is used in image correlation.

Examples:

  1. LAS> avhrrchips in=(somimg,avhrrimg) ints=namerica outmt=na1

    The namerica;tps file will be used to select windows in the base image SOMIMG which are then warped into the AVHRR satellite space of AVHRRIMG. The points selected along with the corresponding chip names are stored in na1;mtp.

Description/Algorithm:

Each tie point in INTS is read. If the point falls within both the base image and the AVHRR image, it will be used to create a chip image. First, a 64x64 window in the AVHRR image space surrounding the tie point is calculated. The latitude/longitude extents of this window are used to calculate a corresponding window in the base image. The window of the base image is then warped into the AVHRR image's space and written out as a 64x64 BYTE chip image. The name of the chip and information regarding the coordinates of the chip and AVHRR image are written to the merged tie point file.

Nonfatal Error Messages:

    None.

Fatal Error Messages:

  1. [avhrrchips-alloc] Error allocating dynamic memory

    An error occurred dynamically allocating memory, which was required for further processing. Contact the system administrator if the problem persists.

  2. [avhrrchips-create] Error creating chip <XXX> for <YYY>

    An error occurred creating the image chip XXX for point YYY in INTS. Ensure there is sufficient disk space to create all the chips.

  3. [avhrrchips-fatal] Fatal error encountered

    A fatal error was encountered during processing. The preceding message explains the exact error.

  4. [avhrrchips-in] Error retrieving <XXX> image of IN

    An error occurred retrieving the base image or AVHRR image of IN. The preceding message will indicate the reason. Respecify the image.

  5. [avhrrchips-invddr] Invalid DDR of base image

    The base image IN(1) must be have a valid DDR to supply projection information for finding locations of tie points. Ensure that the base image is in a valid projection.

  6. [avhrrchips-onebnd] Base image must be a single-band image

    The base image must be a single-band image because chips are one band. Retry, specifying one band in IN(1).

  7. [avhrrchips-open] Error opening <XXX> file

    The tie point selection file or merged tie point file could not be opened. Ensure the tie point selection file exists with read permission, the output merged tie point file does not exist, and the directory where OUTMT will be placed has write permission.

  8. [avhrrchips-read] Error reading <XXX>

    An error occurred reading the specified file. Ensure there is read permission on this file.

  9. [avhrrchips-ret] Error retrieving value of <XXX>

    An error occurred retrieving the value of INTS or OUTMT. The preceding message will indicate the reason.

  10. [avhrrchips-write] Error writing merged tie point file

    An error occurred writing information to the output merged tie point file. Ensure the file and directory have write permission, and that there is sufficient disk space.

User Note:

  1. All output chip images are of type BYTE. If any of the pixel values taken from the base image IN(1) are outside the valid range of values for BYTE data (0-255), negative values will be set to 0 and values greater than 255 will be set to 255.