This paper discusses two aspects of the new DTM generation project, the product view from the perspective of the owner (Ordnance Survey) and the technical solution for combining DTMs from the system supplier (Inpho). Ordnance Survey (OS) has a long history of providing height information in a national context from both precise geodetic levelling networks and photogrammetrically surveyed contours.
The product being discussed here is based on the most recent contour surveys carried out over the period 1970-1983 in support of national mapping series published at 1:10,000 and 1:25,000 scale. Over the life of the product the technical systems used to maintain the data have been updated from analogue capture machines, to analytical and now digital photogrammetry. The most recent development being the purchase of a digital camera. This technology has now come together to create a new height product from both in house data and third party sourced LIDAR. The technical solution to combine the data has been provided by Inpho using the SCOP++ DTM software and the Topographic Data Management system (TopDM) to process the data and place it in a database from which it can be selected for output by accuracy to build the product tiles. This called for some core development work to enhance the system to provide metadata to meet OS business needs and wrapper software to verify and control the input.

Artikelauszug / Extract:

1. INTRODUCTION
Ordnance Survey has an existing height product which has national coverage of both contours and Digital Terrain Models as 10,548 tiles each covering an area of 5x5km2. These were created from contours in the period 1970 to 1983 using aerial photography and were surveyed for use in mapping products at 1:10,000 scale and smaller. The vertical interval was 5m or 10m depending on the terrain. The DTM was created using third party software which also allowed the incorporation of spot heights data mined from the more accurate levelling network and those created during the contour survey. The vertical accuracy (rmse) of both products is quoted as being from ±2.5m to ±5.0m. This product has successfully met national needs for a number of years and has been improved in currency with the survey of significant landscape features such as motorway cuttings and mineral extraction sites.