Re: [Qgis-user] Convert ASCII UK Wind Speed to Raster

Thu, 02 Feb 2012 03:52:27 -0800

On 02/02/2012 01:08 PM, uk52rob wrote:

Hi all,

 

I have been looking into converting the old BERR wind database for a while, but have never had any success. Has anyone tried to convert this data to a raster image using QGIS?


If you're willing to use the GRASS plugin, it's not very hard.

First you need to reformat the files a bit. They are setup with 100 speed estimates, using semicolons as separators as follows

( X, Y );  speed1;  speed2;  speed3; ... ;  speed100

Using a text editor program (vim or anything with a good Search/Replace function), I threw out both of the parentheses. THen I replaced the commas with semcolons, and I removed all the spaces. So I ended up with a file with 102 columns, separated by ';'

X;Y;speed1;speed2;speed3;...;speed100

Now I ran the GRASS  module:

v.in.ascii in=Speed10.asc out=speed10 fs=';'

This gives me a point vector with 100 speed values in 100 columns for each point location. Now you have to decide what to do with the values, in order to interpolate a raster. Do you want to average all values at each point?

It might make more sense to bring the text file - after reformatting - into a database program such as sqlite, or spreadsheet *before* importing into GRASS to calculate additional columns of i.e. mean, max,min, etc. Then import into GRASS with the above v.in.ascii.

The final step is run v.surf.idw or v.surf.rst to get your raster based on one of those aggregate columns.

HTH...

--

Micha

 


 

I have come across the following thread for ArcGIS, but not sure how this would work in QGIS.

 

http://forums.arcgis.com/threads/38041-Converting-ASCII-UK-wind-speed-file-to-a-raster-image

 

Thanks,

 

Rob



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