Building Height Attribute in AutoCAD

Introduction

Background information on OS MasterMap® Topography Layer Building Height Attribute (BHA) and details of the attributes supplied by Ordnance Survey can be found on the Building Height Attribute Overview page.

Getting Started

Download the following datasets for your area of interest from Digimap using the OS download data tab in Digimap:

• BHA data (BHA data is found in the ‘OS MasterMap’ group): select DWG as the format;
• OS Terrain™ 5 DTM or OS Terrain™ 50 DTM: this will be used as the base (surface) heights for the area;
• Optionally download any additional data you may wish to use as a backdrop draped over the DTM surface. We’re going to use OS VectorMap® Local Raster but other datasets could be used.

Visualising the data in 3D using AutoCAD Map 3D

The steps required to visualise the data in 3D using AutoCAD Map 3D are described below:

1 Add OS MasterMap®Topography

1. Open the OS MasterMap® Topography Layer BHA DWG file in AutoCAD Map 3D.

2. At the Open - Foreign DWG file window click Continue opening DWG file.

3. The downloaded BHA data will be displayed.

2 Connect to OS Terrain 5 DTM

• To add in the OS Terrain™ 5 DTM in ASCII format select Data then Connect to Data from the Task Pane:

• This will open up the Add New Connection window:

• Select Add Raster Image or Surface Connection (highlighted in the image above) and browse to the raster dataset supplied by Digimap.
• Ensure the file type drop down is set to Raster files:

• Give your connection a name and press the Connect button:

• At this point it is advisable to set the coordinate system. Terrestrial data supplied by Digimap uses the British National Grid projection.
• The coordinate system is set by clicking on the Edit Coordinate Systems button and then selecting the appropriate projection:

• To display the data press the Add to Map button:

• The DEM will be displayed using a default palette, this can be modified by double clicking on the layer in the task pane to bring up the Style Editor window where you can adjust the colours and number of classes used to display the data.

• Additional raster data can be added using the Connect to Data menu, this will appear draped over the DEM by default (although the resolution may appear relatively poor).

3 The finished visualisation

To navigate in 3D use the Orbit control on the map navigation control bar:

The screen grab below shows the final visualisation centred on Edinburgh using OS Vector Map Local Raster as the surface layer.