May 122015
 
3D Building Heights in ArcGIS

© Crown Copyright and Database Right 2015. Ordnance Survey (Digimap Licence)

We are pleased to announce that users can now download OS MasterMap Building Height Attribute data in file geodatabase format. The data consists of building polygons together with the building height attributes supplied by OS in the latest alpha release of their Building Height Attribute dataset (December 2014 at the time of writing).

This makes the process of visualising the data in 3D much simpler for the majority of GIS users. The file geodatabase format can be read by both QGIS and ArcGIS, including the new ArcGIS Pro, without the need for any complex data processing. Making the data available in file geodatabase format removes the need for users to download building features from OS MasterMap Topography Layer and then use the JOIN function in GIS to connect the Building Height Attribute data to the buildings.

3D Buildings in ArcGIS

© Crown Copyright and Database Right 2015. Ordnance Survey (Digimap Licence)

The data is supplied on a 5x5km grid, so you may receive multiple separate geodatabases if your area covers multiple 5km grid cells, however it is easy to merge the datasets together using common GIS functions.

We hope this makes it much easier to use the data but we welcome any feedback you may have.

  • Email: edina@ed.ac.uk
  • Phone: 0131 650 3302
Oct 312014
 

To get the most from OS MasterMap data it is usually best to convert it from its supplied format, GML, to a format better suited to the software you are going to use it in. For our CAD users Digimap has been offering the DWG format for several months (see previous blog post); now we are offering a format that makes the data easier to use in GIS software.

Although Shapefile is still the most commonly requested GIS format it cannot handle the large file sizes (over 2GB) that could be requested from the Data Download service; an area of 100km2 in an urban centre would exceed this limit.  We therefore turned to the File Geodatabase format that works in the two most commonly used GIS software applications, ArcGIS and QGIS. There is more information about Geodatabases on Wikipedia here: Wikipedia -ArcGIS Geodatabase

To select the File Geodatabase format, add some MasterMap to your basket in Data Download. Once in the basket you can click the down arrow in the Format column and change it from the default GML to File Geodatabase:

File Geodatabase in Data Dowload

Geodatabase formats are the recommended formats  for use in ArcGIS software, being the most efficient for data storage and analysis. The format supports the use of .lyr files for styling the data and EDINA has provided some for the MasterMap data downloaded from Digimap.

The data can be added to a map in ArcGIS and QGIS in the usual way, though in QGIS you need to use Add vector layer –> Directory rather than a Database as you may assume.

Opening a Digimap File Geodatabase in QGIS

Styling information for both ArcGIS and QGIS has been provided by EDINA in .lyr and QML formats, these can be found at the bottom of Digimap’s help page for OS MasterMap. These representations give enough information to view the data in a style that OS MasterMap is commonly viewed in. The help page also contains a link to the official Ordnance Survey SLD styling information, please see the PDF that comes with the SLD files for information on how to use them.

There are help pages for adding styling information here:

If you require any help on using File Geodatabases from Digimap or any other dataset or format then please get in touch:

  • Phone: 0131 650 3302
  • Email: edina@ed.ac.uk
Jul 222013
 

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.

Digimap Data Download Basket

Click image to view full size.

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.

Image showing FME Workbench converting GML to DWG

Click image to view full size.

1: Shapefiles

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:

Image of VML in ArcMap

Click image to view full size.

A simple set of Layer Files has been created for use in ArcMap and can be downloaded from the VML Help page.

2. DWG

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:

Image showing VML in DWG in AutoCAD

Click image to view full size.

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.