SPOT 5 data for line map updating: New perspectives in mapping



7 Map updating method and performance using SPOT 5
Line map updating is the key cartographic application which is now possible using SPOT 5 images with outstanding performance.

The interesting scales are 1/50 000 and 1/25 000 scales which are, for most countries, the scales of the base national maps.

The method :
1:25 000 scale map updating was tested several times by IGN and GDTA very successfully.

The methodology, developed by IGN in the 90s for lower scales, is the following:
  • Scanning of the old map master films with a very high resolution. These master plates (nowadays master films) are the printing elements of paper maps. There is one master film per colour to print the paper map, i.e. one master film for the blue containing all elements of the map printed in blue (hydrography), one for the green containing all vegetation information, one for the black (the richer master films with all buildings, roads,..), one for the bistre containing all contour lines, etc…The number of master films is variable, depending on the country and the type of map. Each master film is like a layer containing a type of information displayed in one colour, so separated from the others and so much easier to be updated.
  • Geocoding of the raster scanned master films;
  • Ortho-correction of the corresponding SPOT 5 2.5 m image using Reference3Dâ or the old map and contour lines;
  • Superposition of scanned master films, with a transparent background, over the SPOT orthoimage;
  • Digitizing of new features, masking of features which do not exist any more;
  • Integration of vector corrections into each master films using the proper graphic symbol.

ă CNES, IGN, GDTA & A. Husseini
Picture n°3 : 1:20 000 scale map updating using SPOT 5 THX image (Beirut, Lebanon: from top to bottom, the old map (1973), the SPOT 5 image (2003) with over the black master film, and the updated map (2003).

The output of the process is a set of digital master films, ready to be combined during printing to obtain the updated paper map. The digital master films are available for the next updating a few years later. The picture n°3 presents a test done by IGN and GDTA to update a 1:20 000 scale map of Beirut (Lebanon): in the middle of the picture one can see the SPOT 5 image with one master plate over (the black one containing the main planimetric information). This showed how useful the Spot Image is, especially over areas where it is impossible to fly with a plane.

The performances:
In July 2004, IGN carried out map updating of a 1:25 000 scale map in real conditions in situ at the Serbian Survey (Vojnogeografski Institut - VGI - Belgrade) using a SPOT 5 THX image (merge between a 2.5-m Panchromatic image with a 10-m colour image). The results were the following :
  • 3280 new buildings, many changes in the road network were digitized;
  • very good fitting between the Serbian map and the SPOT 5 orthoimage;
  • the sheet rapidly checked on the field;
  • updated map ready for printing;
  • all the updating process and rapid field checking in two weeks!
A huge benefit compared with a traditional method which requires months for one map updating. The cost, compared with a traditional method using aerial photos, is approximately divided by five.

8 Use of Reference3D to extract new maps
Reference3Dâ and SPOT 5 data are currently used as "foundation data" by several governments (including the French one) to extract vector maps at a 1:50 000 scale over areas which cannot be reached easily. The rough production principle, designed to minimize the cost of the source images, as well as the production efforts, is to divide the area to be mapped into several equal-density zones, and to affect to each zone a given source image: Reference3D orthoimage for the low density, SPOT 5 m or 2.5 m for the middle or middle+ density, and to keep the 1-m imagery (Ikonos, QuickBird,…) to the very minimum extent needed, over the very dense areas. This is done in the frame of multilateral production groups (MGCP, FDB,…)


ăCNES, VGI, IGN, IGNFI 2004
Picture n°4 : map updating of a Serbian 1:25 000 map. 1- The old map 2- The SPOT 5 THX orthoimage 3- In violet, the new updated features 4- The updated map.

9 Conclusion
As a consequence of the Satellite Revolution, map updating of 1:25 000 or 1:50 000 scale maps is now an easy process to achieve, with moderate costs and rapid results. In this developing market, SPOT 5 data are precious because they combine and optimize the advantages of a good cartographic system (large field of view, excellent geometric properties, very high resolution) with the satellite advantages (revisit capabilities, worldwide availability). At the same time they offer global reference data packages to ensure the best accuracy. These new tools and techniques will probably definitively change the way we map our world.

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