Individual features are not explicitly modelled in the 3D mesh. The mesh will include representations of the terrain, buildings, vegetation, and other features as part of one continuous 3D surface. Individual features can be overlaid onto the mesh using two-dimensional OS products such as OS MasterMap and the OS National Geographic Database (OS NGD). Using these tools, 3D analysis can be used in conjunction with attribute data to gain new insights.
For example, a local council planning department could analyse mesh data to determine the impacts of building a new block of flats at an early stage of the planning process. 3D mesh data can be used to discover local areas that would have their views and environment impacted as a result of the proposed construction project. These areas could subsequently be intersected with 2D address data so that the households and businesses affected could be contacted as part of citizen participation in the planning process.
There is no distinction between terrain (i.e. the ground surface) and other features (for example, buildings) in the mesh. The terrain model is a continuous surface coloured using the source imagery provided which will give a visual indication of whether it is vegetation (for example, grass), bare earth, or fabricated surface (for example, tarmac).
Building geometry is part of the continuous 3D mesh. Even though the imagery used to create it is taken from a nadir viewpoint, the pixels in the image towards the edges of each frame are taken from a slightly oblique viewpoint. In many cases, the combination of multiple overlapping images from different viewpoints makes walls and roofs visible as textures within the 3D mesh.
The resolution of the source imagery captured for the 3D mesh is fine enough to give a good impression of the geometry and colour of the buildings represented. However, when zoomed in, these features will often have a 'draped' look.
Vegetation is modelled as part of the continuous surface where represented on the terrain. For example, the rendition of a tree will model the crown as a continuous surface rather than individual branches and leaves in fine detail. In contrast with a digital surface model, where the crown of a tree is extruded down to the surface, the 3D mesh will more faithfully model the shape of the crown.
To create the 3D mesh, processing software attempts to match similar points in overlapping images of the same scene. This process relies on features in the scene being consistent and static between overlapping images. This is not the case for all bodies of water. Water surfaces in constant movement will look different from one image to the next. In such areas, where the software cannot differentiate between one section of water and another, the image-matching process will fail.
To accommodate areas of constantly changing water, we perform a classification of the imagery to detect areas of water before those images are applied to the mesh. These areas are then masked out and a representative height is assigned to the water-covered area.
The height applied to bodies of water is taken as the minimum height within the water body as measured from a Digital Surface Model (DSM). The DSM is derived from the same imagery used to create the mesh and water height is manually adjusted where necessary
This overview introduces OS 3D Mesh and gives context for all users – highlighting key features, providing examples of uses, and listing details such as product accuracy, supply formats, etc.
OS 3D Mesh beta data is created from aerial imagery originally captured as part of our national imagery capture program on a three-year cycle across the whole of Great Britain.
OS 3D Mesh can be used within a Geographic Information System (GIS) or 3D modelling software to provide a 3D view of the Earth and features present on the surface. The product has been developed to enable the visualisation of an area and for detailed analysis of complex scenes in disciplines such as:
Urban planning
Citizen engagement
Telecommunications planning (for example, line-of-sight modelling)
Security (for example, viewshed analysis for threat detection at international events)
Asset monitoring and planning (for example, wind farm and electricity pylon location planning)
Flood risk assessment
OS 3D Mesh beta data is derived from imagery captured to update the National Geographic Database. Source imagery is captured at a ground sample distance (pixel size on the ground) of 15cm x 15cm.
The European INSPIRE data specification includes elevation datasets such as gridded digital terrain models and Triangulated Irregular Networks (TINS) but does not include 3D meshes. The OS 3D Mesh can therefore not be provided as an INSPIRE compliant dataset, unless and until INSPIRE brings 3D meshes into its remit.
OS 3D Mesh is available as OGC 3D Tiles. This format (often referred to as Cesium 3D Tiles) is an international standard widely used in both the gaming and geospatial data industries. The product will be created to order and supplied as a download. For large areas, the product will be broken down into smaller units for ease of use.
OS 3D mesh provides a single continuous structure formed from triangular faces and textured using colours from source aerial imagery. The mesh is created using proprietary software and can be supplied in several formats to be loaded into 3D data processing software, such as a GIS or a gaming engine. We can supply data in the ESRI 'slpk' format or the Skyline 3DML format and are working on supplying OGC (Cesium) 3D tiles.
Both ArcGIS Pro and QGIS support the use of 3D Mesh data for geospatial processing; however, support and documentation is lacking when compared to 2D raster images and geospatial vectors. Specialist software may be necessary for some applications involving 3D mesh data, although support for the use of 3D data is steadily increasing.
The mesh supplied by this product is created from high-resolution aerial images initially captured as part of the ongoing programme to update the topographic data in the OS National Geographic Database (OS NGD). These aerial images are captured from flight paths that facilitate the creation of overlapping images.
Standard flight plans on OS NGD imagery capture flights provide 80% overlap in the direction of flight and 30% overlap at the sides (between flight strips). The resulting images allow image matching software to create the 3D mesh models used for this product.
The aerial imagery data used to create the 3D mesh is available for the whole of Great Britain and is updated on a rolling basis every 3 years. For the beta product, a 3D mesh for each area will be created to order from this source imagery. Areas previously created will be available to customers as needed.
If OS 3D Mesh proves to be successful, a future 3D mesh product will be created to cover the whole of Great Britain and will be continuously updated as new imagery becomes available.
The OS 3D Mesh beta is an experimental product and will not be updated.
The positional accuracy of the 3D mesh is dependent upon the accuracy of the underlying imagery, the ground control used, and the software used to create it. The overlapping images used to generate the 3D mesh are captured from an overhead (nadir) perspective and have a nominal ground sample distance (pixel size) of 15cm by 15cm.
All imagery is processed using measurements captured from Global Navigation Satellite Systems (for example, GPS and Galileo) from ground control points with a positional accuracy finer than 10cm in the X, Y, and Z dimensions.
OS has undertaken ground surveys using total stations (theodolites which measure both angles and distances) and other terrestrial surveying equipment, in order to collect a set of checkpoints which can be measured against the OS 3D Mesh.
The positional accuracy of the OS 3D mesh data is estimated as 1.1m RMSE. We will do extensive testing to verify this and we may be able to increase the accuracy in future products, by using higher-accuracy ground control point information.
The imagery used to create the mesh was originally captured for use in the update of topographic features in the OS NGD (National Geographic Database) and related products. We have re-used the imagery to produce the OS 3D Mesh beta product, but, as it was captured for other purposes, please note that it is not optimised for mesh creation.
