Elevation Correction

by pkan

Downloads: 64,344 (30) • Reviews: 11

Version:

1.9

Updated:

Nov 29, 2017

ASTER GDEM

ASTER GDEM

Postby rikicarra » Sat Nov 13, 2010 8:25 pm

I have downloaded some "tiles" of my area (Italy) from the ASTER database (http://www.gdem.aster.ersdac.or.jp/outline.jsp) and placed the tif files in a folder, added that folder in the configuration page of the plugin and tested on one activity. Apparently the plugin is able to recognize the DEM information from ASTER but the elevation information are wrong, every point is about 15 m altitude, while the other DEM (SRTM) are almost correct. The reason why I am trying to use DEM from ASTER is because they claim the DEM is 30 m grid, compared to 90 m grid of SRTM for Italy.
Anybody has experience with ASTER GDEM?

Thank you.
Riccardo
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Re: ASTER GDEM

Postby pkan » Sun Nov 14, 2010 6:29 am

First of all, ASTER GDEM is not quite as good as it might seem at first glance. From the README file that is included in downloads:
Statistically, the ASTER GDEM appears generally to meet its pre-production estimated
vertical accuracy of 20 m at 95% confidence, globally. Some tiles have substantially better
than 20 m accuracy, and some tiles have substantially worse than 20 m vertical accuracy.
The ASTER GDEM contains anomalies and artifacts that will reduce its usability for certain
applications, because they can introduce large elevation errors on local scales. However, in
spite of its flaws, the ASTER GDEM will be a very useful product for many applications,
including those requiring a true global DEM.

METI and NASA acknowledge that Version 1 of the ASTER GDEM should be viewed as
“experimental” or “research grade.” However, they have decided to release the ASTER
GDEM, because they believe its potential benefits outweigh its flaws and because they hope
the work of the user community can help lead to an improved ASTER GDEM in the future.

See also a review at viewfinderpanoramas.org.

However, if you still want to use the ASTER GDEM data with the elevation correction plugin, you should be able to do so by treating it as a custom DEM the way you seem to have attempted. (Install the GDAL plugin, then either use "Add DEM" to add ASTER GDEM files one by one, or put the *_dem.tif files in a directory and use "Add Folder".) Make sure you only add (or put in the DEM folder) *_dem.tif files, not *_num.tif files, since the latter don't contain actual elevation data. Your problems might be due to the plugin interpreting *_num.tif files as elevation data.

Also note that you can use the new elevation correction activity detail page to easily compare elevation data from different DEMs, e.g., SRTM and ASTER GDEM. The detail page is enabled from the plugin settings page.
pkan
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Re: ASTER GDEM

Postby rikicarra » Sun Nov 14, 2010 5:05 pm

pkan wrote:First of all, ASTER GDEM is not quite as good as it might seem at first glance. From the README file that is included in downloads:
Statistically, the ASTER GDEM appears generally to meet its pre-production estimated
vertical accuracy of 20 m at 95% confidence, globally. Some tiles have substantially better
than 20 m accuracy, and some tiles have substantially worse than 20 m vertical accuracy.
The ASTER GDEM contains anomalies and artifacts that will reduce its usability for certain
applications, because they can introduce large elevation errors on local scales. However, in
spite of its flaws, the ASTER GDEM will be a very useful product for many applications,
including those requiring a true global DEM.

METI and NASA acknowledge that Version 1 of the ASTER GDEM should be viewed as
“experimental” or “research grade.” However, they have decided to release the ASTER
GDEM, because they believe its potential benefits outweigh its flaws and because they hope
the work of the user community can help lead to an improved ASTER GDEM in the future.

See also a review at viewfinderpanoramas.org.

However, if you still want to use the ASTER GDEM data with the elevation correction plugin, you should be able to do so by treating it as a custom DEM the way you seem to have attempted. (Install the GDAL plugin, then either use "Add DEM" to add ASTER GDEM files one by one, or put the *_dem.tif files in a directory and use "Add Folder".) Make sure you only add (or put in the DEM folder) *_dem.tif files, not *_num.tif files, since the latter don't contain actual elevation data. Your problems might be due to the plugin interpreting *_num.tif files as elevation data.

Also note that you can use the new elevation correction activity detail page to easily compare elevation data from different DEMs, e.g., SRTM and ASTER GDEM. The detail page is enabled from the plugin settings page.

You are absolutely correct. The problem was that I copied both files for each tile, the _num and the _dem, apparently the elevation that the plugin was using was the _num (which is something like the max error for each node of the grid). I have deleted all the _num files and now it works fine. Thank you for the suggestion.

I will do some experiments and try to judge the quality of the ASTER DEM, compering with other DEMs and with my Edge 705 tracks.
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