A Case Study of Pleiades Tri-Stereo Imagery:

1. 13th International Scientific and Technical Conference From Imagery to Map: Digital Photogrammetric Technologies A Case Study of Pleiades Tri-Stereo Imagery: accuracy assessment, interpretability, 3D modeling potential. Elena Kobzeva, Chief Engineer, Technology 2000 Nadezhda Malyavina, Head of Racurs Production department Petr Titarov, Software developer, Racurs September 2013, Fontainebleau, France

2. A Case Study of Pleiades Tri-Stereo Imagery Contents • Pleiades imagery orientation accuracy assessment • 3D modeling of urban area (the city of Yekaterinburg) • Creating and updating topographic maps using Pleiades imagery

3. Pleiades imagery orientation accuracy assessment • Pushbroom imagery orientation models • Test dataset description • Pleiades imagery orientation accuracy Rigorous, rational polynomial (RPC) and universal pushbroom models Pleiades Tri-Stereo product and ground points set Orientation accuracy of single Pleiades images, stereopairs and the triplet

4. Pushbroom imagery orientation models Pushbroom imagery orientation models Rigorous Universal Replacement

5. Rigorous orientation model Ray reconstruction: Ray vertex (sensor position): Viewing direction:

6. Rational polynomial model (RPC) where are polynomials: The coordinates in the RPC formulae are normalized to fall into the range of [-1;1].

7. Rational polynomial model (RPC) refinements RPC adjustment: bias removal RPC adjustment: affine refinement

8. Universal pushbroom models Parallel-perspective model Direct Linear Transformation (DLT) Affine model

9. Test dataset description Pleiades Tri-Stereo Imagery

10. Test dataset description Pleiades Tri-Stereo Imagery – Bundle Product Pan Image, GSD 0.7 m Pan Image, GSD 0.7 m Pan Image, GSD 0.7 m MS Image, GSD 2.8 m MS Image, GSD 2.8 m MS Image, GSD 2.8 m The images were pan-sharpened using PHOTOMOD

11. Test dataset description Ground points set Ground coordinates accuracy: 0.2-1.0 m RMSE Points measurements in the images accuracy: 1 pixel

12. Pleiades imagery orientation accuracy assessment: methodology

13. Pleiades imagery orientation accuracy: single images Image phr1a_p_201306010719533_sen_624609101-001

14. Pleiades imagery orientation accuracy : single images Image phr1a_p_201306010720166_sen_624610101-001

15. Pleiades imagery orientation accuracy : single images Image phr1a_p_201306010720273_sen_624611101-001

16. Pleiades imagery orientation accuracy: single images Conclusions: Planimetric accuracy of supplied RPC was RMSE 3.1-4.2 m (the specification is CE90 = 8.5 m). The accuracy of 0.8-1.0 m RMSE (i.e. rather close to the limit set by the measurements accuracy) was achieved with a single GCP, applying shift refinement to the supplied RPC model. The accuracy of 0.7-1.0 m RMSE was achieved with 4 GCPs, applying either shift of affine RPC refinement. Further increasing the number of GCPs did not improve the accuracy. The orientation accuracy achieved with universal methods varied over a wide range and was significantly worse than one achieved with RPC and bias removal.

17. Pleiades imagery orientation accuracy: the triplet Triplet orientation without tie points

18. Pleiades imagery orientation accuracy: the triplet Triplet orientation with tie points

19. Pleiadesimageryorientationaccuracy: the triplet Conclusions: Using supplied RPC and no GCPs, the achieved planimetric accuracy was 3.6 m RMSE in the case of involving tie points and 3.8 m without them; the vertical accuracy was 2.2 m in both cases. So involving tie points in the adjustment procedure did not significantly improve the accuracy; Involving GCPs made the difference between adjustment with and without tie points insignificant. The accuracy of 0.7-1.0 m RMSE was achieved with 4 GCPs, applying either shift of affine RPC refinement. Using a single GCP and applying shift RPC refinement, the planimetric accuracy of 0.7-0.8 m and the vertical accuracy of 2.2-2.3 m were achieved. Increasing GCPs number to 4 allowed improving the results but not significantly, the vertical accuracy became of 2.0-2.1 m. Further increasing the number of GCPs did not improve the accuracy. The universal methods are not suitable for stereoscopic (three dimensional) processing of Pleiades imagery.

20. Pleiades imagery orientation accuracy: stereopairs vs. the triplet Triplet orientation (maximum B:H=0.37)

21. Pleiades imagery orientation accuracy: stereopairs vs. the triplet Forward + backward stereopair orientation (B:H=0.37)

22. Pleiades imagery orientation accuracy: stereopairs vs. the triplet Forward + nadir stereopair orientation (B:H=0.25)

23. Pleiades imagery orientation accuracy: stereopairs vs. the triplet Nadir + backward stereopair orientation (B:H=0.11)

24. Pleiades imagery orientation accuracy: stereopairs vs. the triplet Conclusions: The accuracy of orientation of the triplet and of the forward+backward stereopair (i.e. the stereopair with the largest base-to-height ratio) was approximately the same. The accuracy of triplet orientation was slightly better than one of the stereopairs which included the nadir image (so the stereopairs had lower base-to-height ratio).

25. Mapping and 3D modeling of urban areas Creating 3D models • Deriving DEM • Generating orthoimagery • 3D modeling of urban area Assessment of suitability for topographic maps creating and updating • Interpretability assessment • Assessment of objects positioning accuracy • Drawing contour lines

26. Creating 3D models using PHOTOMOD: deriving DEM

27. Creating 3D models using PHOTOMOD: generating orthoimagery

28. Creating 3D models using PHOTOMOD: 3D vectorization

29. Creating 3D models using PHOTOMOD: automatic 3D modeling

30. PHOTOMOD.Object texturing

31. PHOTOMOD. Model texturing using close-range imagery

32. PHOTOMOD. Import of “special” objects

33. PHOTOMOD. Creating 3D model of the city of Yekaterinburg

34. Interpretability assessment Source dataset: Pleiades orthoimagery, 0.5m, RGB Worldview-2 orthoimagery, 0.5m, RGB A3 orthoimagery, 0.1m, RGB Topographic interpretation samples set WV-2, GE-1 andIkonos Scanned topographic plans of scale 1:500, contour interval 0,5 m; Vector topographic maps of scale 1:10 000 , contour interval 2 m

35. Interpretation results

36. Assessment of objects positioning accuracy Source dataset: Pleiades stereopair (9º and-11º), 0,5 m, PAN Pleiades orthoimagery 0.5m, RGB WV2 orthoimagery, 0.5m, RGB A3 orthoimagery 0.1m, RGBas reference data

37. PHOTOMOD.Comparing different types of objects Single-storey private houses Multistory city buildings Pleiades A3 Pleiades A3

38. Interpretability analysis It is impossible to tell residential buildings from nonresidential ones 1.5 m - wide ledges are indiscernible Shape and size of multistory buildings are reconstructed correctly Some architectural forms may be missing (the ledges are shown on one side of the building and missing on the other)

39. Assessment of objects positioning accuracy

40. PHOTOMOD.Drawing contour lines

41. Contour lines verification using reference data Vector topographic maps of scale 1:10 000, contour interval 2 m Contour lines derived from the Pleiades stereopair

42. Topographic mapping and 3D modeling of urban areas Conclusions: • The 3D model created is geometrically accurate and discrete, so it is possible to access separate objects, to set attribute values for them and to perform 3D measurements - in other words, to produce geospatial databases. The model can be used for visualization and for 3D city planning. Stereoscopic measurements ensure better accuracy and interpretability than ones performed in single images, while using tri-stereo imagery reduces “blind zones”. • Pleiades images are suitable for creating and updating topographic maps of scale up to 1: 10000. If additional sources of data are available and field verification is possible, it is possible to create and update 1 : 5 000 scale maps of moderate-sized inter-settlement areas. • Accuracy and interpretability of Pleiades imagery are comparable to ones of WordView-2.

43. Acknowledgement RACURS and TECHNOLOGY 2000 express their gratitude to ASTRIUM GeoInformation Services for the Pleiades Tri-Stereo Imagery Product over the city of Yekaterinburg

44. A Case Study of Pleiades Tri-Stereo Imagery Thank you for attention !