Looking for a colormap for SRTM like OCM Landscape

Question

In Quantum GIS there's an OpenLayers plugin. I would very much like to use the same colormap/scheme/theme used in the OCM Landscape layer and apply it to SRTM image I have.

I checked the the open cycle map website but didn't find any info regarding the color map they used so I wonder if anyone knows how to generate a similar colormap or QML file?

TIA.

Answer 1

Hum, OpenLayers OCM Landscape layers don't use any sort of elevation colour ramp as far as I can see. If you wanted to achieve the OCM effect I think you would do this by making a hillshade layer and then overlaying this with a vector polygon having the same extents as the hillshade layer. Then set the fill of the polygon to a light blue-grey and play with its transparency.

Every so often I have another try at making a colour ramp that mimics Open Cycle Map and I've not been able to get anywhere near it. There is great subtlety in the OCM maps. My efforts are brutal, see attached illustration for a sample. I can let you have the ramp if you think it might be of any use, you might have better luck.

Added later: The colour ramp below is really only a poor sideways look at OCM.

1100    233 228 214
800 241 232 205
700 236 228 198
600 226 221 192
500 213 210 178
400 208 224 190
300 190 230 189
200 200 237 202
100 230 244 228
50  236 241 230
0   242 242 236
nv  255 255 255

The first column contains elevation values and the other three are RGB values. In my case the values in my DEM ran from 0 to about 1100 metres, so you will probably need to do some editing to adapt the first column of the ramp to suit your data. Copy the ramp to a text file ("ramp.txt", for example) and use this to make your elevation-coloured layer. I use gdaldem color-relief to do this.

Load the DEM into QGIS and go Raster -> Analysis -> DEM (Terrain models). Set "Mode" to "Color relief", give the output file a name, set "Color configuration file" to point to "ramp.txt" and hit "OK". This should produce your elevation-coloured GeoTIFF.

With my data the ramp produces the results shown in the picture below. OCM appears to lean heavily on contours to strengthen the illusion of relief, so I have added these to the mix in the picture. The scale is about 1:100,000. If you wish to compare my effort with OCM's open OpenCycleMap in a browser and fly to "Betws Garmon".

My suggestion is that before you do anything with lat/lon DEMs you project them to a CRS appropriate to the area of interest. The Man page for gdaldem is definitely something at which you should look: http://www.gdal.org/gdaldem.html#gdaldem_color_relief

I'll leave the making of the hillshade layer with you, but shout if you get problems with this.

Good luck.

Nick.

Answer 2

Just guessing: You are looking for a style to render the elevation from SRTM data. The maintainer of OpenCycleMap (AndyAllan) would not give away his style to the public. For lower zoom levels, he has taken the NASA Blue Marble pictures, and changed the sea color. For higher zoom levels, you have to try yourself.