User's Guide

GRIDCONV

Convolves two geometric mapping grids into one geometric mapping grid.

Function:

Convolves two geometric mapping grids into a single grid. This is useful when doing image-to-image registration and the raw search image must first be corrected to a map projection, then warped to fit the reference space. The resulting grid may then be supplied to RESAMPLE to warp the raw search image directly to the output reference space.

Parameters:

INGRID

Input grid files. The first grid is applied to the second grid. The first grid must contain polynomial coefficients. The polynomial coefficients are applied (convolved) to the second grid to simulate a double-resampling process. (See User Note 4).

OUTGRID

Output grid file. Geometric mapping grid that can be used by RESAMPLE to reproject the search image directly to the reference space.

Examples:

1. LAS> gridconv ingrid=(grid1 grid2) outgrid=result

   GRIDCONV will read the polynomial coefficients found in GRID1;grid and use them to convolve GRID2;grid to produce a new grid named RESULT;grid.

Description/Algorithm

The polynomial from the first grid is read and applied to create an output grid to be used to avoid double resamplng of an image. With this new grid, the last resampling step may be applied to the original data, not the data that has already been resampled once. This results in a precision corrected image which has been resampled one time only.

Nonfatal Error Messages:

None.

Fatal Error Messages:

1. [gridconv-alloc] Error allocating memory

   An error occurred while trying to allocate memory. Re-run, and if the error persists, contact the system administrator.

2. [gridconv-fatal] Fatal error encountered

   A fatal error was encountered during processing. The error message displayed immediately preceding this message is the specific error encountered. Processing is terminated.

User Notes:

1. It is assumed that the two geometric mapping grids map to the same output projection and that the first grid contains a refinement of the process performed by the second grid.

2. The first grid must contain polynomial coefficients which map the output space to input space.

3. The second grid may be created with any gridding method and does not need a set of polynomial coefficients.

4. GRIDCONV is designed to eliminate a double-resampling of imagery. Typically, an image would be taken to a systematic space for control point selection, which involves a grid generation and resampling step. Control points are then selected and another "error surface" is calculated. Another grid and sampling step is therefore required. Resampling another time (i.e., applying RESAMPLE again) results in an image which may be more radiometrically distorted than it needs to be.