Digimap are running a free webinar, on Wednesday 15th March between 1-1:30pm. The webinar is likely to be of interest to architecture staff and students, who use detailed Ordnance Survey urban map data in AutoCAD. We will: Show you how to download Ordnance Survey map data from Digimap AutoCAD: Discuss issues relating to the use […]
As many of you may be aware, the number of users of the Digimap service using CAD systems has increased considerably over the years. As this user base has grown we have endeavoured to make the data we provide as easy to use as possible in these systems. As part of this effort to continually improve the service we offer, we have made some considerable enhancements to the products we offer for use in CAD systems.
Part of the problem is that there is a proliferation of systems in use under the general banner of â€˜CADâ€™ systems, including AutoCAD, Revit, Rhinoceros, Vectorworks to name a few.Â A common factor between these systems is that they can accept vector data in DWG format, however, the way that DWG data is handled can vary between systems.
A number of our products in DWG format were loading into CAD systems but some were not correctly spatially referenced. This meant that although the data looked fine and worked perfectly well on its own, but it was difficult to overlay or integrate it with other datasets. We have now fixed this issue, so that it is possible to overlay common products together much more easily.
To accompany the DWG map data we also provide Digital Terrain Model (DTM) data to allow you to create a landsurface to loacte buildings and infrastructure on. In the past we only provided the OS TerrainÂ 5 DTM in a format that was not so easily used in some CAD systems. To remedy this, we are now delivering OS Terrain 5 DTM in the XYZ format that can be used in most CAD systems.
These are the Changes we have made:
- All data available as DWG should overlay correctly where appropriate in AutoCAD Map 3D, AutoCAD, AutoCAD Civil, Revit and Rhinoceros.
- All data has the correct Spatial Reference (British National Grid) and Units (metres).
- OS Terrain 5 Contours are available as 3D Polyline data which is suitable for creating surfaces in Revit and Rhinoceros 5.
- OS Terrain 5 DTM is available in an XYZ format which can be used to create surfaces in AutoCAD and Rhinoceros 5.
- OS MasterMap Sites LayerÂ is now available inÂ DWG.
We have updated our help pages in line with these changes and recommend that you consult the AutoCAD FAQ page whichÂ has further details for how you can load Digimap data in to common CAD packages.
We hope our CAD users find these changes useful but if you have any questions about using Digimap data in a CAD system please let us know. Similarly if you can provide us with any information about using Digimap data in a CAD system we would be very pleased to hear from you.
- Phone: 0131 650 3302
- Email: email@example.com
As part of ongoing efforts to improve the usability of data delivered by Digimap, we have made some significant enhancements to one of the Ordnance Survey licensed datasets.
OS VectorMap® Local is a relatively new product from Ordnance Survey providing slightly less detail than OS MasterMap but still very useful for detailed backdrop mapping. Individual buildings are shown as well as roads, rivers, landcover and contours. The vector version of the data is provided by Ordnance Survey in GML 2.1.2. This is a standard geospatial data format developed by the Open Geospatial Consortium; however it generally needs to be converted into a proprietary format before being used in GIS and CAD software.
To make using this data easier we are now providing OS VectorMap Local in both Shapefile and DWG formats. Shapefiles can be easily opened in ArcGIS and most other GIS programs including OpenSource GIS software such as QGIS and gvSIG. DWG is the native format for AutoCAD and can be used in many other CAD systems as well.
This data is now available for download from the Data Download application in the Digimap Ordnance Survey Collection. VectorMap Local is in the Vector Data section; to change the format of the data you are downloading click on the Change link under Options once you have added it to the basket.
Creating the data:
TO achieve the best results when recreating the data in different formats we had to use different software products for different formats. To convert the data to Shapefile we used the OpenSource Software GDAL program called “ogr2ogr” and for the DWG conversion we used FME from Safe Software. The image below shows part of the FME Workbench project used to convert the data to DWG.
To convert the GML to Shapefile we created a lookup table between the Feature Codes in the GML data to Shapefile Layers. As Ordnance Survey do not provide any guidance in their User Guide as to how to group features in VML , we analysed the data and experimented with various groupings, so that in the end we split the data into a possible 22 separate Layers. These layers may contain multiple feature classes but as they all have the original feature codes on them as attributes as well as all the other original attribution, further distinction between features can be achieved for representation and querying.
Example of the Shapefile data in ArcMap:
A simple set of Layer Files has been created for use in ArcMap and can be downloaded from the VML Help page.
To convert the data to DWG we had to go through a similar process (as well as our data team becoming much more familiar with AutoCAD). We originally intended to produce DXF format data but this turned out to be a problem. We had to make some decisions about how to store attribution in the output data and one of the main considerations was the size of the resultant files. To begin with when we converted a tile of VML that was 60Mb of GML, it expanded in size to 240Mb when converted to DXF containing attributes as Inserts. This was unusable in systems we tried so we had to work on ways of making the files smaller. The first thing we did was change the format from DXF to DWG. As both formats are commonly read by various CAD systems this seems a reasonable thing to do although it may make the data slightly less interoperable. This changed the file size to 44Mb for our sample dataset. This was still quite large and some systems were having problems with this, especially when dealing with tiles in dense urban areas. We therefore decided to change the way we were storing attributes in the data. Instead of using Inserts we used Extended Entity Data (or XData) which was one of the options available in FME. This stores a fixed amount of information against an entity in the drawing. We use this to store the attribute information that was in the original GML data, including the original feature code. It’s a bit more difficult to work with this data but it can be viewed in AutoCAD Map 3D by using the Express Tools –> Tools –> List Object Xdata or typing xdlist in the command prompt.
Using XData brought the size of our sample tile down to 10Mb and was usable in all the systems we tested it with. If you need access to the attributes either as Inserts or as Map 3D Object data please let us know.
As part of the conversion process we defined the representation for features in the DWG file, including point symbols and area fills. Features have also been grouped together into separate Layers as we did with the Shapefiles.
Example of the data in AutoCAD:
Finally, after getting the project set up in FME and a thorough testing of the data, we ran the batch process to convert the data. This took nearly 3 days per format to convert the full load of our national coverage of VML data. This data will be updated on the normal update schedule, as we get updated VML from Ordnance Survey as Change Only Updates so future conversions will be much quicker.
Remember,both these datasets are available through Data Download by selecting VectorMap Local and then changing the format after you have added the data to your basket.
We intend to produce alternative formats for other products, including OS MasterMap, so we would very much like to hear your thoughts on the data that we have produced so far and let us know if this meets your needs.