User's Guide

RELIEFX

Corrects ground control points for relief displacement

Function:

Corrects ground control points for relief displacement errors (which are caused by terrain elevation) relative to a specified elevation base for Landsat 1, 2, and 3 MSS CCT-X data which have been geometrically corrected (either system or precision corrected).

Parameters:

INTL
Input tie point location file. This file contains control points which are to be adjusted for the effects of relief. These control points consist of X,Y search coordinates and their elevations.

INGRID
Input grid file. Input geometric mapping grid file containing the geometric mapping grid. This grid is used to map the coordinates into the raw CCT-X space. This grid is generally created by XRECTIFTY or XUTM. This is the same geometric mapping grid which was used to create the geometrically corrected image.

OUTTL
Output tie point location file. This tie point location file contains the adjusted coordinates.

ELEV(0.0)
Elevation. The reference elevation to which the relief displacement is adjusted. Elevation is added to the the reference ellipsoid to create a base elevation which corresponds to a reference plain above the ellipsoids. The default is to add zero meters to the reference ellipsoid. The unit of measure for ELEV is meters.

PRINT("TERM")
Output destination. The destination of the output. The original control points, the elevation, and the control points adjusted for relief displacement errors are displayed.
  = --:        No Report
  = TERM:      Terminal.  Output is sent to the user's 
               terminal.
  = LP:        Line printer.  Output is sent to the 
               printer defined by $PRINTER.
  = Filename:  User-supplied filename.  Output is sent 
               to the user-supplied file with the ex-
               tension ";prt".

Example:

LAS> reliefx intl=control ingrid=grid outtl=adjust elev=1341.12
The tie point coordinates in CONTROL;TPL are read. The coordinates are transformed to the raw CCT-X image coordinates using GRID;GRID. The coordinates are adjusted for relief, using an elevation of 1341.12 meters is used as the base elevation. Finally, the new coordinates are transformed back to the output space and written to ADJUST;TPL. The results are displayed on the terminal.

Description/Algorithm:

Tie points are read from INTL. The search coordinates for each point are transformed to the raw CCT-X image space using INGRID. These points are then adjusted for relief displacement using the same algorithm that RELIEF2 uses (see RELIEF2 for more details) with the exception that the nadir pixel calculation is not needed. This is due to the fact that the nadir pixel is always pixel number 1610 for a full MSS-X scene. If ELEV is specified, the relief displacement is calculated using this elevation as a reference. Finally, these points are transformed back to the space that the tie points were selected in by using the inverse mapping. The results are written to OUTTL and PRINT.

Nonfatal Error Messages:

None.

Fatal Error Message:

[reliefx-fatal] Fatal error encountered
The message displayed immediately preceding this message is the specific error encountered. Processing is terminated.

User Notes:

RELIEFX is used to correct for errors due to relief displacement in control points in Landsat 1, 2, and 3 MSS CCT-X imagery. Control points will be corrected to a reference elevation as specified by ELEV. By correcting the control points, relief distortions contained in the control points are not introduced into the geometric model. To correct for relief in the imagery, a pixel-by-pixel adjustment must be performed (TPGEOM). If a pixel-by-pixel terrain correction is to be performed, ELEV should be equal to zero.
See RELIEF2 for more description on the algorithm.