Working with DEM Models Qgis Quantum GIS

Below you will find a few tips on working with DEM models in Qgis. Image taken from http://earthexplorer.usgs.gov/ of Big Island Hawaii

You download your GeoTiff file and it looks like this:

 

Screenshot from 2013-07-11 09:52:36

 

 

To fix it right click on the layer>properties>Style Tab. Under contrast enhancement choose StretchtoMinMax

 

Screenshot from 2013-07-11 10:12:55

 

 

 

It should look like this:

Screenshot from 2013-07-11 10:14:08

Still not much but better. This is an image of The Big Island Hawaii . The lighter the color the higher to elevation and the darker the color the lower. Since this is an island the dark is water in this case

Let’s run a few raster analysis tools to learn more about it.

First let’s calculate slope. You can either express slope as a percent or as is. If you have issues when creating your raster analysis and it comes out looking much like a tv screen with static you need to convert the unit of the layer to the units of the map. If you map is in meters then it is 111120. If it is in feet 370400. It is input whenever you see this box here:

Calc

Slope as a percent:

slopeaspercent

Slope

 Slope

For this exercise I used a scale of 111120 to convert it to meters

Next we can add contours to the map:

Raster>Extraction>Contour

When choosing an interval be careful. It is going to generate a line shapefile that can be very large so just play around and see what work for your project and make sure to include it somewhere on the map or you can label the contour lines also.

I used 100 meter intervals to create this map. I also turned off the layers so it can be seen better

contour

These are just a few of the tools available in Qgis. Feel free to leave a comment requesting help or any other tutorials.

3 Responses to “Working with DEM Models Qgis Quantum GIS”

  1. Ourizo says:

    And what about the best option to get a DEM from a contour line shapefile??. I´ve tried from de the Raster>interpolation Menu but with the TIN option I dont get any results and the IDW option offers a not too good result.

    I´ve read somewhere I would need to rasterize the vector layer and then proceed to an interpolation with Grass. Is there a good and direct option to interpolate contour lines?.

    Thanks!

  2. Andy says:

    I have had similar issues and converted the contour lines to points, which had the Z value assigned. I then created a new interpolated DEM raster from this and then the DEM

  3. Anil Agashe says:

    I have a dem raster layer taken from USGS. The data is in DDM (Degree Degree Meter)format. How can I convert it to MMM (Meter, Meter, Meter) format?

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