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Chris Proba - orthorectification
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Chris Proba - orthorectification
11/11/11 9:16 PM
Hi again!

in the line of my previous post (geometric correction / telemetry file), what I really want to do is to orthorectify a Chris Proba image. As I undertood by the BEAM Help, the sequence is:

1) First, use the Chris Proba geometric correction tool using a telemetry file
2) GPC points have to be defined on the image (the resulting image of the geometric correction tool)
3) Use the orthorectification tool

Is this procedure correct? Once you put GPC points on the displayed image, the orthorectification tool recognize them?

About the orthorectification tool I have some extra questions:

a) can I use another DEM different to GETASSE30 Elevation Model? I would like to use an ASTER DEM

b) what are the tie-points grid? what are the implications of reprojecting them?

Thank you very much and sorry for the avalanche of questions!

virginia
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RE: Chris Proba - orthorectification
11/14/11 9:48 AM as a reply to VIRGINIA ELENA GARCIA MILLAN.
Hi Virginia, the correct sequence for doing the orthorectification of CHRIS/Proba images is:

  1. Define ground control points for your scene
  2. Do the CHRIS/Proba geo-correction
  3. Do the orthorectification by means of the BEAM reprojection tool


The ground control point have to use WGS 84 coordinates, and be sure that you do not use the target altitude when doing the geo-correction. Unfortunately you cannot use the ASTER DEM instead of the GETASSE30 DEM, unless the file formats are the same.

The tie point grids resulting from the CHRIS/Proba geo-correction tool provide viewing angles and latitude & longitude per pixel (each pixel is a tie-point). When they are reprojected, they become usual band, but you do not need to reproject the tie points anyway.
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RE: Chris Proba - orthorectification
11/14/11 1:47 PM as a reply to Ralf Quast.
Hi Ralf!

I found in the BEAM Help that the data format for the GETASSE30 DEM is
binary, 1800*1800 signed 16-bit integer values, big endian order
. If I want to use the ASTER DEM, I have to be sure that the format is the same, right?

Concerning that the resolution of the GETASSE30 DEM is 30 arcsec, if I define the Target altitude in the GPC points manager with a better resolution DEM, as ASTER's, activating "use target altitude" should provide better accuracy than the GETASSE30 DEM in the orthorectification tool, right?

What is your opinion?

Thank you for your previous answers!

vir
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