12th International Scientific and Technical Conference

From Imagery to Map: Digital Photogrammetric Technologies

September 24–27, 2012, Algarve, Portugal

Modern DSM creation algorithms in DPW’s

Andrey SechinScientific Director, Racurs

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

Local methods

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Local methods: advantages & problems

Pros: no special memory requirements fast subpixel accuracy in “smooth” regions.

Cons: problems in untextured regions, with horizontal patterns, with repetitive patterns discontinuities – the main problem.

Local methods: example

GeoEye-1 (0.5m) stereo satellite imagery

Global methods

E = E(data) + E(smooth)

E(data)- measures photo consistency

E(smooth)- measures smoothness. Penalties for small and large disparity changes

NP hard problem

Two epipolar images are considered

Global methods: dynamic programming

We cut energy function into scan lines.

This gives very fast computing speed.

The result is horizontal streaks in the disparity map.

Global methods: graph-cuts & belief propagation

We minimize energy approximately.

Graph-cuts are not computationally efficient.

Belief propagation generally does not converge but can computationally be very efficient.

Global methods: SGM & simple tree

We approximate energy and find the best solution strictly.

Memory requirements for SGM = w*h*dmax.

Filtering and smoothing is required.

Special algorithms and modifications for multiple images, or for pushbroom sensors.

Global methods: PHOTOMOD approach

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

Thank you for attention