The new methods of dense DTM creation in PHOTOMOD

Andrey SechinScientific Director, Racurs

September 2013, Fontainebleau, France

DEM, DTM, DSM, nDSM

DEM, DTM have different definitions in different countries.In Russian (по-русски) ЦМР, ЦМП

DEM & DTM - bare earth terrain. DSM include tree canopy & buildings.nDSM = DSM - DTM

PHOTOMOD. Different models (depending on algorithm)

Automatic DSM (old cross-correlation algorithm) with filtering buildings and trees

Automatic DSM (old cross-correlation algorithm)

3D semi-automatic model (with manual stereo vectorization)

Different models for Novokuznetsk city GeoEye-1 stereopair (GSD 0.5m)

Local algorithms of DTM creation

Local algorithms

Memory efficient Fast Subpixel accuracy in

“smooth” regions Problems with periodic

structures and poorly textured regions

Big problem with discontinuities on images

Global algorithms of DTM creation

Global algorithms

Global energy minimization Take into account discontinuities and

hidden surfaces Not memory efficient Still require filtering and smoothing in

the end of algorithm

E = E(data) + E(smooth)

Semi Global Matching (SGM) Graph-cuts Simple Tree Iterative- deformation method

(RACURS)

PHOTOMOD: iterative deformation method (IDM)

All images are taken into account simultaneously

Memory efficient

Image pyramid hierarchy is used for speed and reliability

Image resection is used to calculate occlusions

Still requires filtering and smoothing on the final step

Local vs Global method

SGM andIterative deformation methods

CrossCorrelation

SGM example

Stereopair and disparity map

IDM: GeoEye example

Cross Correlation

IDM

IDM: Pleiades example

IDM: Pleiades example

IDM: DMC aerial example

GSD = 6 cm

IDM: DMC aerial example

GSD = 6 cm

IDM UltraCam example

GSD = 7 cm

RMS difference betweenLIDAR and DSM – 21 cm

IDM UltraCam example

IDM UltraCam example

Thank you for attention