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

HighHigh QualityQuality SmoothSmooth ContourContour LinesLines

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

Thank you for attentionThank you for attention!!