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1

Here is an approach in R. It is computationally expensive and very slow when applied to large rasters. Because of this, I added a point sub-sampling approach that seems tractable. I should note that, because the raster needs to be coerced into a vector, this function is not memory safe. This function returns the percent volume data and not a contour, but ...


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Provided you have the Spatial Analyst or 3D Analyst extension installed, you can use the Contour tool. This allows you to set an interval as you require. This will create contours over your whole raster. Then you can easily select those between 700 and 1000 using Select By Attributes.


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Simple method: Rename the file(s) to csv or asc to see the tables (you may need to edit each one and add a header line), create a feature class from XY table (or make XY event layer) then perform a Point to Raster (your cellsize is 15 metres), this will give you a DEM. With the DEM run GDAL_Contour or Esri contour: gdal_contour -i 10 ...


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For the contour creation, see How to create contour lines from point data? You can add Natural Earth shapefile boundaries (or any other shaoefiles) as background, or Openstreetmap tiles via the Openlayers plugin.


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About a year ago i've been created a video how to make contour lines from points with qgis. Available here: http://youtu.be/w4fEewn7gz0 Language: hungarian :D


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Contours are a model of the surface, a DEM is also a model of the surface, debating the relative inaccuracies of one model vs another seems a bit pointless. Contours don't exactly follow the same elevation on the source DEM and are usually generalized or smoothed for a more cartographic appearance, if you try to compare them in the Z with a DEM both are ...



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