Updating and Improving the Accuracy of a Large 3D Database Through the Careful Use of Gcps and Icesat Data : Example of REFERENCE3D

Abstract

Onboard SPOT 5, the HRS instrument systematically collects stereopairs around the Globe since 2002. Each stereopair can encompass an area up to 600 km x 120 km within a single pass (i.e. 72 000 km2 stereoscopic strips). From this time, SPOT 5 stereoscopic imagery becomes one of main satellite data sources for accurate DEM extraction. Spot Image and French National Cartographic Institute (IGN) decided in 2002 to design and build a worldwide accurate database called Reference3DTM using HRS data. This database consists of three information layers: Digital Elevation Model at 1-arc-second resolution (DTED level 2), Orthoimage at 5m resolution and Quality Masks. Huge efforts have been made to standardize the process in order to offer affordable prices. From 2002 to 2008, the targeted accuracies were 16mCE90 for circular horizontal accuracy, and 10mLE90 for elevation accuracy. These accuracy requirements were achieved without any control points nor map support, as demonstrated by numerous scientific assessments of the Reference3D products performed by independent users. The introduction of the paper briefly reminds the most significant assessments performed by major players within the geospatial community, and more specifically the one by ImageONE Co., Ltd.(Tokyo) on two Reference3D geocells over the Northern coast of Japan, Hokkaido province. This work was published in 2008 during the last Beijing ISPRS congress. In 2009, it was decided to introduce reliable GCPs within the Reference3D production process, to increase the horizontal accuracy down to 10mCE90. In addition, two new layers were added to the product, which provide the user with i) the horizontal accuracy for every single pixel of the Reference3D orthoimage and ii) the vertical accuracy for every single elevation value within the Reference3D DEM. The paper shows how the extensive use of ICESat data, correctly selected and filtered, brings extremely valuable information regarding the effective vertical accuracy, and how ICESat data allows to fully quantify the elevation accuracy of a dataset. This will be illustrated by the presentation of the V&V works that took place over the above quoted 2 geocells in Hokkaido province. In conclusion, we present the road map for the update of the whole Reference3D database, which currently spreads over more than 45 millions of sq. km. (being more than 4,200 1° by 1° geocells), already funded and started up to 2014, towards 80 M km2 of Reference3D products.