VIIth International Scientific and Technical Conference From Imagery to Map: Digital Photogrammetric Technologies ADS40 imagery processing using PHOTOMOD: technology and experience Petr S. Titarov, Software Developer September 17-20, 2007, Nessebar, Bulgaria
Report outline • ADS 40 image acquisition • Software involved and data flows • Solving space intersection and resection problems • Processing ADS40 using PHOTOMOD • Pilot project: creating 1 : 2 000 orthoimagery
ADS 40 Level 0 imagery Level 0 image Exterior orientation w X f Y ADS40 Level 0 images are distorted due to pushbroom imaging mode and exterior orientation instability. Z k
ADS 40 Level 1 imagery creating The Level 1 image is generated by projecting Level 0 image onto the constant height plane in the Local Space Rectangular (LSR) reference frame using in-flight (not adjusted) exterior orientation.
Level 0 vs. Level 1 Level 0 image Level 1 image As compared with Level 0 images, the Level 1 images are non-distorted,comfortably viewable, suitable for automatic tie points measurement.
Specific aerial pushbroom imagery artifacts On the edge of the image Inside the image The gaps on the ADS40 Level 1 images are caused by abrupt exterior orientation change. AN-30 Level 1 images edges L-410
Data flows between software involved Sensor calibration (*.cam) In - flight exterior orientation (*.odf) Ground control and tie points GPro Level 0 imagery creation, automatic tie points measurement ORIMA Block adjustment Level 1 imagery creation PHOTOMOD Level 1 imagery + metadata (*.sup) + sensor geometric calibration (*.cam) +in-flight exterior orientation (*.odf) Adjusted exterior orientation (*.odf.adj) DTM/DEM extraction, 2D/3D vectorization, orthoimagery creation
GPS/IMU software, GPro, ORIMA… GPS/IMU software Post-processing of the in-flightGPS/IMU measurements: • POSProc/ POSGPS • GrafNav GPro Image download from on-board storage, Level 0/1 imagery generation ORIMA ADS 40 block adjustment
PHOTOMOD Software PHOTOMOD DTM DTM derivation PHOTOMOD StereoDraw 3D Vectorization PHOTOMOD Mosaic Orthomosaic generating PHOTOMOD Vector Digital map creating
Space intersection and space resection problems Space intersection Space resection Space intersection is solved to derive DTM. Space resection is solved to create orthoimagery.
Solving space resection problem by Level 1 image Level 1 space resection solving scheme Level 0 space resection Solving Level 0 space resection problem is time-consuming operation due to pushbroom image acquisition mode and the instability of the airborne sensor exterior orientation. The procedure consists of three stages: • Iterative contracting the search area (estimating line and detector number ranges); • Sequential line number search throughout the range; • Calculating detector number using line number found;
Solving space intersection problem by Level 1 stereopair Level 1 space intersection solving scheme
Selecting images for processing in PHOTOMOD Stereo processing 14 ̊ backward + nadir nadir + 28̊ forward 14 ̊ backward + 28̊ forward B : H = 0.25 B : H = 0.53 B : H = 0.78 Best correlation, butworst stereo precision Best stereo precision, but worst correlation Orthoimagery creating Orthoimagery should be created using nadir images to minimize the influence of DTM errors on the orthoimage accuracy.
PHOTOMOD project structure for ADS 40 processing Since the block adjustment of ADS 40 data is performed by ORIMA, there is no reason to insert the entire block into single PHOTOMOD project. Project structure in the case of stereopair composed of nadir and off-nadir images Project structure in the case of stereopair composed of backward and forward images: the nadir image is added into separate strip. The orthomosaic is created using capability of PHOTOMOD Mosaic module to involve images from several PHOTOMOD projects.
Adding ADS 40 images into the PHOTOMOD project Automated folder analysis and data search Radiometric enhancement
Focus on reference systems Local Space Rectangular PHOTOMOD project reference system The exterior orientation is given with respect to LSR (Local Space Rectangular) reference system.So the connection between PHOTOMOD project reference system and LSR should be provided.There are two ways to establish the connection: • To measure at least three points with known ground coordinates on the stereopair (shift –rotation – scale seven parameters set will be calculated); • To specify completely the PHOTOMOD project reference system - datum, map projection etc.
Pilot project: 1 : 2000 orthoimagery production Source data • images GSD: 20 cm • strips number: 24 • data (L0&L1) volume: 0.5 Tb Output orthoimagery • scale: 1 : 2 000 • sheets number: 351 • orthoimagery area: 91,25 km2 14 ̊ backward + nadir stereopairs were used to derive DEM for orthoimagery creating
Pilot project: workflow GPS/IMU post-processing In-flight exterior orientation data preparation STEP BY STEP GPro Level 1 imagery generating Block adjustment ORIMA PHOTOMOD Montage DesktopPHOTOMOD AT PHOTOMOD projects creating PHOTOMOD DTM DTM extraction from stereopairs Deriving orthomosaic using images and DEMs from several PHOTOMOD projects PHOTOMOD Mosaic
Pilot project: check points • points number : 15 • strips number: 24 • images GSD: 20 cm • X,Y mean errors: 20 cm • Z mean error: 30 cm
Pilot project: orthoimagery samples Panchromatic Color
Thank you for your attention! THE END