I have found some open source data of mean wind speeds for the UK at 10m, 25m and 45m. I've shared the zip folder to my dropbox which you can download at:


My issue is that I have no idea how to view the .asc files in QGIS - I receive an error

"...is not a valid or recognised data source"

I've tried taking the first line/header out of the files and saving them but I get the same error. Is it correct that these files will result in a raster output rather than a set of vectors?

  • 3
    Here's a link to a script I wrote a very long time ago. Should still work geonet.esri.com/thread/19004
    – user2856
    Apr 18, 2017 at 20:11
  • @Luke - So by using QGIS and with the files in my download folder, would you be so kind as to explain how I get the code to relate to the files? I've never used python before and I feel a bit put off by it!
    – James B
    Jun 8, 2017 at 12:22
  • 1
    You don’t use qgis, you use python from the command line. python dti_windspeed.py path/to/inputfile path/to/output.asc
    – user2856
    Jun 8, 2017 at 12:51
  • Sorry for being ignorant, but I thought python was only accessed from qgis. I really don't have any idea what I'm supposed to do.
    – James B
    Jun 8, 2017 at 15:15
  • Assuming you are using Windows. Find where python.exe is. Open Windows Explorer, navigate to where you saved the script and data. Hold shift key, right click that folder and select "open command prompt here" . For each dti asc file type C:\path\to\python.exe dti_windspeed.py input.asc output.asc Obviously changing input.asc to the real filename and output.asc to what you want to call the new file. You can then convert the new files to Raster in qgis
    – user2856
    Jun 8, 2017 at 20:54

1 Answer 1


Sadly the DTI seem to have invented a new format and used an existing well known extension for it.

An Ascii grid file (a raster) would start with 6 header lines and then the data. These files contain:

Each ASCII file has a header line with information about the source file, file type etc.

Subsequent lines in the file have the appearance:
(Easting, Northing) speed; speed; speed; etc.
Easting The East co-ordinate to the first value in the line
Northing The North co-ordinate for that line
speed Is the wind speed estimate for the kilometre square in m/s.
There are 100 wind speed estimates in each line of the ASCII file. East is incremented by 1 for each new wind speed estimate. Each of the wind speed estimates is delimited by the character ';' so that other software packages may separate each of the wind speed estimates. This is a fixed-width data file.

Which has to be one of the worst file formats I've ever seen. I think you will need to write some custom code to read this junk.

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