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    Lidar data - ASCII to GeoTiffs

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    We have just released our latest 1m and 2m DTM Composite products on the DEFRA DSP. This includes the best available surveys captured before October 2019. With the 2019 release we have changed our data format from ASCII to GeoTiffs. These GeoTIff files are supplied in 5km tiles with elevations in metres. GeoTIFF is a modern GIS format widely used for delivering elevation data and was chosen due to its open standards and highly efficient data storage. Data volumes are on average 5x smaller, enabling faster download over internet and more manageable storage. Storing the data in GeoTiff also enables us to start to deliver more services over the web such as Image Services and WCS services. These services provide APIs for users view the data directly in a browser, or bring the data directly into desktop GIS and perform geoprocessing analysis on it. The old ASCII format meant we were limited to what we could offer. Moving to GeoTiff format also aligns the Composite product to our National LIDAR Programme products.

     The vast majority of software’s including QGIS, ArcGIS, GRASS & AutoCAD Civil3D are able to open a GeoTiff file in the same way as the previous ASCII file. If you do experience any issues we have put together some links on converting between file formats on the Blogs and Guides section of our storymap. This is a straightforward conversion process in GIS software or can be achieved with a few lines of code.

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    • Avatar
      Ian Williams

      Hi Ella,
      This change is causing me a real headache. The old ASCII files were dead easy to read and required no special software. I don't (yet) know much about the GEOTIFF format, but I can't open a TIF file with a text editor or easily read the data into my own software. This move isn't helping to democratise the data. Assuming I ever manage to figure out a way of reading a GEOTIFF file (without having to resort to a third party application), does the format give me xyz point coordinate values as the good old ASCII files did or is it just some image file?

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      Data Services Platform team

      Hi – It’s not possible to open the GeoTIFF file and extract information using basic windows software. The GeoTIFF file format can be opened in QGIS – A free and open source GIS software package. From this you could easily convert back to ASCII if you have specific software you have written that you want to open it in. The GeoTIFF file can also be read using python gdal libraries to extract the XYZ position of each pixel if you are importing into your own software or convert back into ACSCII.
      The GeoTIFF File provides a XYZ position for the centre point of the pixel to the exact same positional accuracy as the previous ASCII files. As mentioned in the FAQ moving to GeoTIFFS means out LIDAR data can be support more modern web GIS applications as well as being significantly smaller which helps with storage, download and transfer costs.

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      Ian Williams

      Hi Ella,
      Thanks for your reply. I've since figured out how to import the new data format into my Mathematica notebooks. I hear what you say about using third party conversion tools such as QGIS, etc. but would prefer not to if possible as things start to get messy if flipping between several different software applications. I do think it's a shame that you've dropped the ASCII format as it was very accessible. Why not just provide the data in both formats?

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      Data Services Platform team

      Unfortunately the DSP isn’t currently able to support multiple download formats on the open data side for raster data. It would be fantastic if both formats could be offered however this would require both formats to be stored on the system and processed adding significant storage costs and resource time to enable this. As an organisation we have also moved away from using ASCII data and we no longer store newly captured LIDAR data in this format.
      Many thanks
      Ella

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      Michael Eldred

      Hello Ella,
      My GIS software supports GeoTIFF but when I download lidar data from the DEFRA website and open the .zip I get 8 files none of which are .geoTIFF or anything like it. In case it's not obvious, I know virtually nothing about the workings of GIS and am currently at a loss to know how else to get the data that used to work so easily with .asc files. Can you help please?

    • Avatar
      Michael Eldred

      Hello Ella
      Problem sorted no need to respond

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      Data Services Platform team

      Thats great, thanks for letting me know