An issue with DEM terrain models

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An issue with DEM terrain models

Giacomo Fontanelli-2
Hi everybody

I'm using a SRTM 4 (Geotiff, Int16 - Sixteen bit signed integer) and QGIS 2.18.1.

I tried to produce a slope map using Raster > analysis > DEM (terrain model).

In case I would like to have degrees as output i obtain a map with values from 89.5 to 90 degrees only, so almost impossible to classify.

In case I flag the option"Slope expressed as percent" I obtain a map with more pixel values, but the slope is expressd with numbers from 0 to1971690.

What's the problem?

Thank you

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Re: An issue with DEM terrain models

Carlos Cerdán
Hi Giacomo

Perhaps the SRC of your DEM is ESPG4326 (lat-long) if so, vertical units are meters and horizontal units are degrees, then the relation between vertical and horizontal units is 111111, and you must put that value in the "scale" option. It is because 90° = 10'000,000 m (one cuarter of meridian).

Saludos

Carlos



2017-03-09 11:13 GMT-05:00 Giacomo Fontanelli <[hidden email]>:
Hi everybody

I'm using a SRTM 4 (Geotiff, Int16 - Sixteen bit signed integer) and QGIS 2.18.1.

I tried to produce a slope map using Raster > analysis > DEM (terrain model).

In case I would like to have degrees as output i obtain a map with values from 89.5 to 90 degrees only, so almost impossible to classify.

In case I flag the option"Slope expressed as percent" I obtain a map with more pixel values, but the slope is expressd with numbers from 0 to1971690.

What's the problem?

Thank you

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[hidden email]
List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user


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