I was wondering if there is a way to make an Autocorrelated DEM within QGIS or Grass. I am looking to do this with stereo aerial photography. I am able to do this with a number of COTS tools, but I am looking for an open source solution. If you know of other tools I am open to suggestions.
asked Mar 29, 2013 at 15:28
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3What is autocorrelated DEM?– SS_RebeliousCommented Mar 30, 2013 at 9:51
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2@SS It is a DEM automatically created from a stereo pair by using local correlation calculations ("autocorrelation") to determine the parallax. (I remember seeing an application do this in "real time" at a computer graphics show c. 1989: using a very high-end system, it could process a megapixel image pair in just a few seconds. :-)– whuberCommented Apr 3, 2013 at 17:18
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2 Answers
Autocorrelation is achieved by software 'matching' pixel for pixel from each of the image stereopairs. The diff XY co-ords of each, compared to their neighbours, are used to determine elevation variations.
The quality of the result varies, depending upon the scale of the source imagery, the quality & resolution of the sensor, the type of terrain it covers.
SocetSet (BAE), Imagestation (Intergraph), Match T (Inpho), LPS (Er4das) and UltraMap (Microsoft) are recognised s/w suites that include autocorrelation modules. However they are not stand-alone & with required base modules, cost an arm & a leg, and used only by professional geophysical/mapping organisations. Speed of the process is largely dependent upon the resolution required.
Autocorrelation can't 'see through' trees, will follow the contours of buildings. bridges etc. - i.e. good for orthoimage production.
Each of the above s/w suites include tools that enable quite smart filtering of much of the above 'artifacts', and manual tools for further editing (stereo-breaklining) and other refinements where a pure terrain surface is required (i.e. contours, volumetrics etc.).
I have never heard of a open-source option.
Not sure what you are exactly looking for but check this module:
http://grass.osgeo.org/grass64/manuals/r.surf.fractal.html
It creates a fractal surface of a given fractal dimension.
