processing earth observing images with ames stereo...

Newly added in our recent 2.3 releaseof ASP is the utility ‘pc_align’. Thisutility implements the iterativeclosest point (ICP) algorithmthrough the use oflibpointmatcher library. Thisallows users to align theirASP created DEM againstpreviously trusted densesources like SRTM, USGSNED, or GMTED. This sameutility can be used to align aDEM to sparse source likeGLAS, LOLA, or MOLA viainput from CSV.

The example shown rightaligns a DEM created fromWorld View 2 imagery (2m/px) of the CathedralRange in California to aprior existing USGS NEDmap (30 m/px). The top leftslice is the ASP created DEMwhile the bottom right is thetrusted reference.

Processing Earth Observing images with Ames Stereo Pipeline

Ross.A.Beyer@nasa.gov http://irg.arc.nasa.gov/ngt/stereo

Affine Script:> stereo <image1> <image2> \

<camera1> <camera2> \<output prefix> \--alignment affineepipolar

Get Ames Stereo Pipeline

Aligning Output to a Trusted Source Science Accomplished with ASP

Methods of Ingestion

Map Projecting Script:> mapproject -t rpc <dem prior>

<image1> <camera1> <mimage1>> mapproject -t rpc <dem prior>

<image2> <camera2> <mimage2>> stereo <mimage1> <mimage2> \

<camera1> <camera2> \<output prefix> <dem prior>

Script:> pc_align --max-displacement <meters> <dem prior> <asp dem> \

--save-transformed-source-points -o pc/pc> point2dem -tr 2.0 -t_srs "projection" pc/pc-trans_source.tif

Script:Reference against geoid

> dem_geoid <dem>

Reference against ellipsoid> dem_geoid <dem> \

--reverse-adjustment

Vertical Datum Support

Script:Follow QR code in top rightcorner or go to:

http://irg.arc.nasa.gov/ngt/stereo

to find download link for yourspecific OS.

> Download StereoPipeline.tar.bz2> tar xf StereoPipeline.tar.bz2> export PATH=$PATH: \

StereoPipeline/bin

Read the Manual!

> open StereoPipeline/*.pdfor

> gvfs-open StereoPipeline/*.pdf

Ames Stereo Pipeline (ASP) has for along time been able to create denseelevation models for Planetary Scienceon non-terrestrial bodies. Now we’veadapted our tools for Earth Science andcan process imagery from Digital Globe,

GeoEye, Astrium, and anything elsewith an RPC model readable by GDAL.

You can download ASP to perform yourown work from our website by followingthe instructions bellow. ASP is Apache

2 licensed (free as in beer) and operateson most forms of Linux and OSX. It issuitable for operation on yourcomputer, the head-less server, or youruniversity cluster.

Processing satellite imagery into a pointcloud is performed with ASP’s ‘stereo’command. It requires two images withdifferent perspectives in NTF or any otherimage format. It also accepts XMLmetadata that describes a rigorouscamera model that is often shipped withDigital Globe data.

The stereo command will by default try tocorrelate, match all pixels betweenimages, without modifying the inputimagery. However that can take a lot oftime and will possibly fail if there is arotation or scale difference betweenimages. Instead it is recommended thatthe input images be epipolar rectifiedusing the “--alignment affineepipolar”option. An example of its effect is shownright.

Alternatively, for difficult stereo pairs, ASPcan use prior existing low resolution DEMfor map projection. The stereo commandis smart enough when generate its pointcloud to reverse the projection arithmeticand then triangulate with the morerigorous camera model.

By default, all data created by ASP isreferenced against an ellipsoid model. ForEarth data this is usually WGS84. Howeverthis is not ideal for watershed analysis as anellipsoidal model does not correctly modelthe changes in gravity across the surface ofthe Earth.

Instead the solution is to use geoid, a lumpymodel that describes mean sea level in theabsence of weather and tides. ASP providesa utility, ‘dem_geoid’, which can be used toreference data against the commonly usedEGM96, NAVD88, or if processing Marsdata, MOLA MEGDRA.

Our team desires to make elevation productsfor all imagery. However we don't have thetime or experience to apply ASP to allapplications. This is why NASA offers ASPcompletely free. We hope to enable thescientific community access to additionalmeasurements that couldn't be hadotherwise due to cost or data volume. Forexamples of ASP used by the community,please follow the sources on the right.

Check out "Monitoring changes in polar ice sheetsand sea ice using airborne and satellite remote

sensing" by Shean et. al. Friday morning, C51A-0498.

Samantha E. Peel, Caleb I. Fassett, "Valleys in pitcraters on Mars: Characteristics, distribution, andformation mechanisms", Icarus, Volume 225, Issue 1,July 2013

N.P. Hammond, C.B. Phillips, F. Nimmo, S.A.Kattenhorn, "Flexure on Dione: Investigatingsubsurface structure and thermal history", Icarus,Volume 223, Issue 1, March 2013

Watters, W. A., L. Geiger, and M. Fendrock. "ShapeDistribution of Fresh Martian Impact Craters fromHigh-Resolution DEMs." LPI Contributions 1719(2013): 3081.

Lefort, Alexandra, et al. "Inverted fluvial features in theAeolis-Zephyria Plana, western Medusae FossaeFormation, Mars: Evidence for post-formationmodification." Journal of Geophysical Research:Planets (1991–2012) 117.E3 (2012).