Advances in DTM Creation Advances in DTM Creation and Processing Methods and Processing Methods in PHOTOMOD 5in PHOTOMOD 5
Alexey ElizarovDeputy Head of Software Development Department
September 2010, Gaeta, Italy
Xth International Scientific and Technical Conference From Imagery to Map: Digital Photogrammetric Technologies
DTM CreationDTM Creation
Typical DTM step of about 10—100 metresCorrelator-based algorithm for corresponding point search on a pair of images
PHOTOMOD 4.x → 5.0 improvements:Significant improvement of corresponding point search algorithm to increase robustness of the obtained heights.Search in triple overlap areas and inter-strip stereopairs followed by automatic filtering of excessively dense points.
PHOTOMOD 5.0 → 5.1 improvements:see the slides to follow...
DTM Computation InterfaceDTM Computation Interface
Simplified DTM computation setup windowPresets for the most common terrain and imagery types:
ruralurbanmountainous...
HeightHeight ComputationComputation forfor LinearLinear ObjectsObjects ProblemProblem
When correlation coefficientreaches its maximumon a straight line,no certain point matchcan be found...
...if we have noadditional information.
HeightHeight ComputationComputation forfor LinearLinear ObjectsObjects
PHOTOMOD 5.0 PHOTOMOD 5.1in-strip stereopair
epipolar line direction
Corresponding point search on epipolar lines
Robust height determining for linear objects directed at large angles to epipolar lines
Points on linear objects are discarded as unreliable.
HeightHeight ComputationComputation forfor LinearLinear ObjectsObjects
epipolarlinedirection
PHOTOMOD 5.1inter-strip stereopair
PHOTOMOD 5.1all stereopairs
Inter-strip stereopairs give heights of objects that are “weak” in in-strip stereopairs.
Processing all stereopairs gives heights of all objects(a case of multiimage matching).
BuildingsBuildings andand VegetationVegetation FilterFilter
Removes points on non-terrain objects such as buildings, plants.
Yellow points: “good” points left by the filter.Red points: “bad” points removed by the filter.
DenseDense DTMDTM
Dense DTM step is nearly equal to the imagery GSD.
Dense DTM creation steps:1. Computation of a preliminary
dense DEM2. Filtering the preliminary DEM3. Interpolating the DEM
Dense DTM creation is accomplished by:New correlator-based algorithm of fast computation of dense modelUses benefits of NVidia CUDA technology of GPGPU parallel computations:17 megapixels per minute on Tesla C1060 / Quadro FX5800.
Dense model filtration algorithmDense model interpolation algorithm
Dense DTM allows more accurate filtering out non-terrain objects.
DenseDense DTM DTM CreationCreation
Preliminarydense DEM Filtered DEM Interpolated DEM
Excessive details Higher quality
LaserLaser ScannerScanner DataData ImportImport fromfrom LAS LAS filesfiles
Unlimited data volumeArea of interest selectionPossibility to split the result into sheets
FurtherFurther DevelopmentDevelopment ofof DTM DTM CreationCreation MethodsMethods
Moving to image recognition approaches.
Techniques:Dynamic programmingSignal filtration theory
Advantages:Increasing accuracyIncreasing robustnessDSM creationAutomation of object extraction and classification