1 Using Reference3D in mapping projects L. Falala IGN France International

2 Medium-scale cartography from 1/250,000 to 1/100,000  Simple process: - Global DEM like SRTM or Reference3D: 30-90m resolution - Medium resolution satellite images like Spot5 or Rapideye: m resolution - Orthorectification of satellite images - Plotting of Geodatabase features directly on orthoimages - Map edition  Altimetric layer: Global DEM - SRTM: from 56º South to 60º North, 3” resolution (90m), freely distributed - ASTER GDEM: 99% of land areas, 1” resolution (30m), freely distributed - Reference3D: >50M km2, 1” resolution (30m), public price: 2-3 US$/km2  Cheap process: a few US$/km2 for data + processing costs  Is it accurate enough for medium-scale cartography ?

3 Impact of DEM accuracy on map quality  Planimetric accuracy of orthoimages depends on: - Ground control points - DEM accuracy  DEM accuracy: - SRTM: 16m at 90% - Reference3D: 10m at 90%  Orthoimages: - Plani error < 20m with viewing angle < 40º Map Scale1/250,0001/200,0001/100,000 Data planimetric accuracy50m40m20m  Paper Map accuracy: 0.2mm

4 Impact of DEM accuracy on map quality  Spot heights: altimetric accuracy = DEM accuracy  Contour interval must be aligned with DEM accuracy: - 20m interval minimum with SRTM and Reference3D  Hill shading and contour lines quality depends on: - Accurate rendering of local shapes in DEM: no blocked valleys, no rounded crests lines - Absence of artefacts in DEM (SRTM void data)

5 New 1/200K maps of Senegal  “PCS200” project: - Conducted in by IGN-FI and mapping agency of Senegal - Financed by European Union - Production of a GeoDatabase and 27 new maps at 1/200,000  Methodology: - Altimetric reference layer: Reference3D DEM - Orthoimages calculated from Spot 5 panchromatic images at 5m and Landsat colour images at 30m - Spot heights interpolated from DEM and distributed every 10km - Hill shading image calculated from Reference3D - Contour lines with 20m interval automatically extracted from Reference3D, automatically smoothed and manually edited

6 New 1/200K maps of Senegal  30m Reference3D DEM20m interval contour lines

7 New 1/200K maps of Senegal  Hill shading from Reference3D DEM

8 New 1/200K maps of Senegal  No GCPs coming from existing maps or field survey  Only tie points with Reference3D

9 New 1/200K maps of Senegal  Checking accuracy: - GPS points and GPS recordings of vehicles during field completion phase -  Consistency of maps and GPS always better than 15m  Success of the project: - 27 maps produced in due time and within specifications - Inexpensive data + simple methodology - Know-how transfer to local institutions -  EU is funding comparable mapping project in Burkina Faso in 2011

10 Old and new map of Kolda (extract)

11 Old and new map of Nioro du Rip (extract)

12 Old and new map of Kaffrine (extract)

13 Mosaic of the 27 new maps

14 Conclusion  For Medium Scale Mapping, altimetric layer can come from Reference3D  Whatever the mapping project: do not understate 3D information - Impact on what you put on the map - Impact on map accuracy

15 IGN France International 39 ter, rue Gay Lussac PARIS France Tél : Fax : IGN France International 8 rue du Sentier PARIS France Tél : Fax : Thank you for your attention Laurent Falala: