Dear Leo
This is a question that only the Japanese are likely to be able to answer
in depth. However, if there is simply an offset in x and y, you could try
finding a few few control points and compare the Easting and Northing of
them to the coordinates in the image, then find an average offset in
Easting and in Northing, separately. Then shift the center point by those
two amounts (Easting and Northing separately)in the .ers file header, and
the images and maps should overlay. However, this won't be very accurate
unless the residual errors are just a simple translation of a plane from
image to map. If it is worse than that (including rotation, for instance) I
think you will just have to use a number of control points and resample the
image to the map. The z-component accuracy will depend on their DEM
generation software and whether it is every-pixel-measured or not, among
other things. You could try adding the average offset in z to all
elevation values in the image for the crudest approach to correction, but I
don't guess the .ers file for an ASTER DEM has a z-value for the image
center, and you will have to employ a formula from the annotation window to
do it.
Your Friend, Bob V.
At 10:09 AM 1/21/02 -0800, you wrote:
>Dear list,
>
> I have an Aster relative DEM. This is the first time I have worked with
>this data, and if anyone has any insight on how to handle this data, it
>would be greatly appreciated. I currently have a DEM, in the same area with
>small overlap, that was extracted from rectified topographic maps, but I
>noticed that the Aster DEM needed to be shifted slightly in the horizontal
>and vertical direction. The questions I have up front is; how do you move
>the DEM in the vertical direction, say 20 meters increase in elevation, so
>that all pixel values in the DEM increase by 20? Also, does the Aster DEM
>need to be georeferenced with the use of GCP's, or does it just need to be
>shifted in the horizontal X & Y, and the vertical Z, for correct elevation?
>
>Thanks in advance for any help,
>
>
>
>Leo M. Romeijn
>Satellite Imaging Corporation
>121 Hawkstone Rd.
>Woodland, WA, USA 98674
>(360) 225-0625 ~ (360) 225-0833 (Fax)
>[EMAIL PROTECTED]
>Web: http://www.satimagingcorp.com
>
>
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