Anybody had experience of QGIS? Apparently it can be used to extract contour data from Google Earth- is this a practical proposition?
Thanks
Richard
QGIS
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Re: QGIS
I am an experienced GIS user (ArcGIS) and QGIS is more-or-less an OpenSource version of this with similar functionality. Google Earth generally uses an underlying terrain model derived from SRTM - this used to be fairly crude height information but I read that 30m grid is now available but I cannot determine from looking at the UK if this has been applied. A much easier approach is to download free height data from the OS. OS Terrain 50 is available (along with many other free data sets) from https://www.ordnancesurvey.co.uk/openda ... ducts.html It can be downloaded as contours in shapefile format - these can be imported directly into OCAD. Alternatively download ASCII and use the DEM Import Wizard in OCAD. Another option is to pay a small sum of money (and it is small) to download OS Terrain 5. I use http://www.emapsite.com which is also great way of viewing data sets including OS MasterMap.
I have been knocking together OCAD maps for recce purposes using various free data sources including OS OpenData and for Scotland Historic Land Use data and National Forest Inventory (and limited OpenStreetMap). Some head up digitising is needed to add fences and tracks as these are currently not available free as far as I can determine.
I should add I am a novice OCAD user but the map is a usable document.
I have been knocking together OCAD maps for recce purposes using various free data sources including OS OpenData and for Scotland Historic Land Use data and National Forest Inventory (and limited OpenStreetMap). Some head up digitising is needed to add fences and tracks as these are currently not available free as far as I can determine.
I should add I am a novice OCAD user but the map is a usable document.
Fac et Spera. Views expressed are not necessarily those of the Scottish 6 Days Assistant Coordinator
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Freefall - addict
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Re: QGIS
Thanks Colin, I'll take a look, although a lot of this whistles straight over my head!
To reply to myself: the method I've seen using QGIS doesn't look suitable for orinteering maps. You basically draw a continuous line in the form of a grid over the area and use it to sample the associated data, a kind of transect. The grid would need to be about 5m between lines I suppose, for the level of detail we need, and it's just not practical.
Cheers
Richard
To reply to myself: the method I've seen using QGIS doesn't look suitable for orinteering maps. You basically draw a continuous line in the form of a grid over the area and use it to sample the associated data, a kind of transect. The grid would need to be about 5m between lines I suppose, for the level of detail we need, and it's just not practical.
Cheers
Richard
- RichardE
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Re: QGIS
Richard - you got it. Even if you took lots of sampling points from Google Earth you are not going to get a good terrain model as you will not improve on the accuracy. My recommendation - download the OS Terrain 50 data from the OS and import the ASCII files into OCAD12 using the DEM Import Wizard. It's a good starting point.
Fac et Spera. Views expressed are not necessarily those of the Scottish 6 Days Assistant Coordinator
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Freefall - addict
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Re: QGIS
I have used QGIS and it works a treat. Download the Environment Agency DTM data. This has a grid of heights at various resolutions. 2m is OK but it will obviously miss small features. (Goodness knows why full UK coverage does not exist.) Extract the relevant .asc file for the OS squares you are interested in. In QGIS use the Layer-Open Layer-Open Raster to import this file, or use the chequered icon, and select the datum. Then use Raster-Extraction-Contour menu item. I now extract 20cm, 1m & 5m contours separately. 20cm is useful for some line features. The default is to create ESRi .shp files into a folder but you can change this to create .dxf files. I find the QGIS folder / filename selector somewhat bizarre as well as some other aspects of the user interface. A .dxf file can be IMPORTED into OCAD9. This comes in as unsymbolised objects so they need to be selected and given a symbol. I created 3 new symbols for this. The actual 5m contours for the map or line features can then be created from these using skill and judgement?
Ideally I would like to put all the .asc files into one folder and then run a script that generates and saves all the 3 .dxf files suitably named. I have had some success with doing this manually but I think it should be easy to automate this process but my computer skills are not good enough at present and I do not have time to learn. I'm sure it should be possible to run the script using QGIS in the background.
Attached doc gives some more details. Hopefully one of the computer wizards can come up with a method that does what I want.
Ideally I would like to put all the .asc files into one folder and then run a script that generates and saves all the 3 .dxf files suitably named. I have had some success with doing this manually but I think it should be easy to automate this process but my computer skills are not good enough at present and I do not have time to learn. I'm sure it should be possible to run the script using QGIS in the background.
Attached doc gives some more details. Hopefully one of the computer wizards can come up with a method that does what I want.
- John-O
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Re: QGIS
As this thread mentions OS Mastermap; "parts soon to be freely available":
https://www.governmentcomputing.com/social-media/news/government-opens-os-mastermap-help-businesses-utilise-geospatial-data
https://www.governmentcomputing.com/social-media/news/government-opens-os-mastermap-help-businesses-utilise-geospatial-data
- Nimby
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