September 2013, Fontainebleau, France 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

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

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

Pushbroom imagery orientation models Rigorous Universal Replacement

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

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

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

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

Test dataset description Pleiades Tri-Stereo Imagery Parameters Images Image ID DS_PHR1A_201306010719183 _ SE1_PX_E060N56_0920_01800 DS_PHR1A_201306010719416 _ SE1_PX_E060N56_0920_01876 DS_PHR1A_201306010719523 _ SE1_PX_E060N56_0920_01876 Imaging date and time 2013-06-01 07:19:53.4 2013-06-01 07:20:16.6 2013-06-01 07:20:27.4 Viewing angle along track 10.1° -2.7° -8.5° Viewing angle across track 1.4 ° 1.9° 2.1 °

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

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

Pleiades imagery orientation accuracy assessment: methodology Scheme # GCPs number Orientation model Objective I RPC Supplied RPC accuracy assessment II RPC + shift Assessment of accuracy achievable using supplied RPC and tie points (but no ground control) III 1 Assessment of accuracy achievable with RPC and a single ground control point IV 4 RPC + affine Assessment of accuracy achievable with RPC and the typical ground control point configuration, applying affine refinement V To compare the efficiency of affine and shift RPC refinements VI 10 To find out if the accuracy improves with increasing the number of ground control points in the case of applying shift RPC refinement VII To find out if the accuracy improves with increasing the number of ground control points in the case of applying affine RPC refinement VIII all available Assessment of the best achievable accuracy in the case of applying shift RPC refinement IX Assessment of the best achievable accuracy in the case of applying affine RPC refinement X Affine Assessment of accuracy achievable with the affine universal model and a minimal set of ground control points, and comparison with orientation with RPC (the ground control points set was the same as in Schemes III and IV). XI Parallel-perspective Assessment of accuracy achievable with the various universal models and comparison with orientation with RPC (the ground control points set was the same as in Schemes V and VI). XII DLT XIII

Pleiades imagery orientation accuracy: single images Image phr1a_p_201306010719533_sen_624609101-001 Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m I RPC - 33 3.1 4.9 III 1 RPC+shift 0.0 32 1.0 2.3 IV 4 RPC+affine 0.4 0.5 29 1.9 V 0.6 0.8 2.0 VI 10 0.7 23 1.1 VII VIII 2.2 IX 0.9 X affine 2.6 4.2 XI par.persp. 1.3 3.9 XII DLT 1.2 1.7 3.0 XIII 1.6 2.4 1.8 3.4

Pleiades imagery orientation accuracy : single images Image phr1a_p_201306010720166_sen_624610101-001 Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m I RPC - 38 3.9 4.6 III 1 RPC+shift 0.0 37 0.8 1.5 IV 4 RPC+affine 0.1 0.2 34 0.7 1.7 V 0.3 0.4 VI 10 0.6 0.9 28 1.3 VII 0.5 VIII 1.4 IX 1.2 X affine 4.5 7.6 XI par.persp. 2.0 4.1 2.5 4.4 XII DLT 3.0 XIII 2.8 4.8 5.7

Pleiades imagery orientation accuracy : single images Image phr1a_p_201306010720273_sen_624611101-001 Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m I RPC - 38 4.2 5.4 III 1 RPC+shift 0.0 37 0.9 1.8 IV 4 RPC+affine 0.1 0.2 34 0.8 2.1 V 0.3 VI 10 0.5 28 0.7 VII 1.9 VIII IX 0.6 1.7 X affine 6.6 11.3 XI par.persp. 2.8 5.8 3.7 6.3 XII DLT 2.6 2.3 4.7 XIII 3.9 6.5 4.0 7.9

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.

Pleiades imagery orientation accuracy: the triplet Triplet orientation without tie points Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ I RPC - 38 3.8 2.2 4.9 III 1 RPC+shift 0.0 37 0.8 2.3 1.3 5.3 IV 4 RPC+aff. 0.1 34 2.0 4.3 V 0.3 1.6 0.5 2.1 0.7 1.5 4.4 VI 10 0.6 1.4 1.1 2.5 28 VII RPC+affine 1.0 2.7 2.4 1.8 5.0 VIII 5.9 IX 1.2 6.1 X affine 13.5 51.4 36.9 125.6 XI par.persp. 11.5 5.5 23.7 3.4 13.7 7.3 34.3 XII DLT 0.9 3.1 1.9 19.1 49.3 XIII 10.3 5.1 21.4 3.5 12.9 7.2 30.1

Pleiades imagery orientation accuracy: the triplet Triplet orientation with tie points Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ II RPC+shift - 38 3.6 2.2 4.5 5.7 III 1 0.2 0.6 37 0.7 1.4 5.6 IV 4 RPC+affine 0.1 34 0.8 2.0 4.3 V 0.3 1.6 0.5 2.1 1.5 4.7 VI 10 1.1 2.4 28 2.3 5.4 VII 5.2 VIII 1.2 5.0 IX X affine 0.0 8.0 38.0 19.3 67.8 XI par.persp. 28.7 9.5 64.2 31.9 12.6 95.2 XII DLT 30.5 7.4 67.3 34.6 11.1 106.2 XIII 30.9 70.5 33.8 13.6 105.8

Pleiades imagery orientation accuracy: 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.

Pleiades imagery orientation accuracy: stereopairs vs. the triplet Triplet orientation (maximum B:H=0.37) Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ I RPC - 25 3.6 2.0 4.5 4.9 III 1 RPC+shift 0.0 24 0.8 2.2 1.2 5.3 IV 4 RPC+affine 0.1 21 0.7 1.1 4.3 V RPC+ shift 0.3 1.6 0.5 2.1 1.9 1.4 4.0 VI 10 0.6 1.3 15 0.9 VII 4.4

Pleiades imagery orientation accuracy: stereopairs vs. the triplet Forward + backward stereopair orientation (B:H=0.37) Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ I RPC - 25 3.5 1.9 4.5 4.3 III 1 RPC+ shift 0.0 24 0.8 2.2 1.3 4.9 IV 4 RPC+affine 0.1 0.2 21 0.7 2.0 1.1 4.7 V 0.3 1.7 0.6 1.4 3.6 VI 10 1.2 15 1.0 3.9 VII 0.5 2.1 4.0

Pleiades imagery orientation accuracy: stereopairs vs. the triplet Forward + nadir stereopair orientation (B:H=0.25) Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ I RPC - 25 3.3 2.6 4.2 7.7 III 1 RPC+shift 0.0 24 0.8 2.8 1.4 7.8 IV 4 RPC+ affine 0.6 21 0.7 2.2 1.2 6.4 V 0.4 1.6 0.5 2.5 1.3 6.3 VI 10 1.5 1.0 2.4 15 2.7 6.7 VII 6.5

Pleiades imagery orientation accuracy: stereopairs vs. the triplet Nadir + backward stereopair orientation (B:H=0.11) Scheme GCPs count Orient. model GCP RMSE, m GCP MAX, m CPs count CP RMSE, m CP MAX, m dS dZ I RPC - 25 4.1 3.5 4.9 9.4 III 1 RPC+shift 0.0 24 1.0 3.0 1.7 8.0 IV 4 RPC+ affine 0.2 1.8 0.3 2.5 21 0.7 3.4 1.5 10.1 V 0.4 2.7 0.6 4.0 3.3 1.2 8.8 VI 10 2.4 4.6 15 1.4 VII 0.5 2.2 4.3 2.9 7.8

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).

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

Creating 3D models using PHOTOMOD: deriving DEM

Creating 3D models using PHOTOMOD: generating orthoimagery

Creating 3D models using PHOTOMOD: 3D vectorization

Creating 3D models using PHOTOMOD: automatic 3D modeling

PHOTOMOD. Object texturing

PHOTOMOD. Model texturing using close-range imagery

PHOTOMOD. Import of “special” objects

PHOTOMOD. Creating 3D model of the city of Yekaterinburg

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 and Ikonos Scanned topographic plans of scale 1:500, contour interval 0,5 m; Vector topographic maps of scale 1:10 000 , contour interval 2 m

Interpretation results Imagery Number of recognized objects Images only Add. Info Field ve-rification Not re-cognized Pleiades 103 92 21 20 WV 2 106 90 19 A3 126 78 15 14

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, RGB as reference data

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

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)

Assessment of objects positioning accuracy Parameter WV2 ortho Pleiades ortho Pleiades stereo Number of measurements 371 366 Mean error, m 1.3 1.5 0.9 Maximum error, m 4.0 5.4 3.5 Error distribution – vector map of scale 1: 2 000 Error distribution – vector map of scale 1 : 5 000 0-0,4 mm 0.4-08 mm larger than 0.8 mm 0-0,4 mm 0.4-08 mm larger than 0.8 mm

PHOTOMOD. Drawing contour lines

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

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.

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

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