3D mapping from space?
Prof Dr Armin Gruen, Dr Kirsten Wolff
(c3) Identification and mapping of individual map features
We have pointed out that neither the goals nor the procedures of 3D mapping are clearly defined yet. The available new technologies require a totally fresh approach to mapping.
Satellite images are an interesting source for 3D mapping. However, they still do have a number of substantial disadvantages when compared to aerial images. As spatial and hopefully also radiometric resolutions improve in the future their suitability for landscape model generation and for medium scale topo-mapping has to be continuously evaluated.
In our tests with manual mapping from IKONOS stereo images we found problems in reproducing small geo-morphological details in contours, especially in cases of vegetation covering the bare earth. From these satellite images less map features could be interpreted compared to aerial images, and definitely not with the same reliability. However, the experienced topographer, using empirical knowledge, including also the special characteristics of the country, found many more features than we expected. All in all the IKONOS images were not sufficient for the production of 1:25,000 map data. But even if we consider that satellite images are already now available at the same spatial resolution as aerial images (WorldView-1 with 0.5 m GSD) we still have to take into account the lower radiometric quality of satellite data. Especially digital aerial images provide us with a hitherto unsurpassed image quality, which is very crucial when it comes to the interpretation of map features.
However, these statements refer to the map specifications of Switzerland. In other countries these specifications may not be as stringent.All the previous results were obtained by manual measurements. We should clearly understand that we are currently still very far away from any reliable procedure of automated landscape model or map generation. This remains a key topic for further research.
• Fraser, C., Dorji, T.,Gruen, A., 2008: High resolution satellite mapping for spatial information generation in Bhutan. Paper accepted for presentation at the XXIth ISPRS Congress, Beijing, 3-11 July, Commission VI, WG 6.