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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.

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2 Answers 2

up vote 4 down vote accepted

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.

enter image description here

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.

enter image description here

Nick.

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That looks quite nice Nick. If you don't mind sharing the color ramp, I'd appreciate a copy. –  n1kn0k Aug 11 '12 at 12:18
    
Hey @nhopton. Bumping this message to remind you about the colorramp you mentioned. :) –  n1kn0k Aug 12 '12 at 8:48
    
Done, see above. N. –  nhopton Aug 12 '12 at 12:50
    
One more thing I learned just now is how "nv" is supported in color ramps. Thanks for that, too. In case other people wants to try Nick's color ramp, you may encounter errors on QGIS as it is. Try this instead: pastie.org/4463409 –  n1kn0k Aug 13 '12 at 0:54
1  
A qualified success? You might get better results if you load the elevation-coloured layer first, with no transparency, then load the contour layer on top of this. Then load the hill-shade on top of all of the others and set its transparency to around 80 or 90 per cent. N. –  nhopton Aug 14 '12 at 8:46
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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.

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Well, basically, I'm just looking for a neutral colormap theme/scheme to use for visualizing SRTM data. It just happens that his scheme was something like that. I wouldn't mind using some other colormap or similar if there's any to be found. –  n1kn0k Aug 10 '12 at 5:49
1  
Maybe this tutorial is helpful for you: geo-works.de/2012/03/… –  Andre Joost Aug 10 '12 at 6:54
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