LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
DOCUMENTATION
OF
LS3D - LEAST SQUARES 3D SURFACE MATCHING
SOFTWARE
How to
co-registration and comparison
of
terrain data sets?
by
Devrim Akca
www.photogrammetry.ethz.ch
Chair of Photogrammetry and Remote Sensing (P+F)
Institute of Geodesy and Photogrammetry (IGP)
Swiss Federal Institute of Technology Zurich (ETHZ)
Wolfgang-Pauli-Strasse 15
CH 8093 Zurich
2008, Zurich
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
•
•
NOTE THAT
Property of the training data set belongs to the Chair of Photogrammetry and Remote Sensing of
ETH Zurich. They can not be published without permission.
The LS3D uses float variables for the point coordinates. If X-Y-Z coordinates are in UTM or in a
similar long form, appropriate leftmost 3 or 4 numbers must be truncate from the coordinate values.
DATA IMPORT:
•
Run the Ls3D software by double-clicking the executable.
•
Set the data directory by clicking the File/Workspace menu button.
•
Click the File/”Convert from ASC to Binary XX2” menu button. Before starting to the
conversion, be sure that all data files have “*.ASC” or “*.asc” suffix.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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There are two data files in our project directory.
4strips_esri_1m.asc
LI_DMC_1M_DSM_ACX_CROPPED.asc.
The first files is in ESRI ASCII grid format, the second one is regular grid pointcloud.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
•
Select the “4strips_esri_1m.asc” file by clicking the mouse. From the “ASCII file internal
format” combo box, select “ESRI ASCII Raster” option. Click the “Batch Mode – Convert
THIS” button. A process runs…
The file was successfully and automatically converted to xx2 format.
The conversion details can be seen in the file “4strips_esri_1m.asc.xxx_ConvInfo.txt”.
•
Select the “LI_DMC_1M_DSM_ACX_CROPPED.asc” file by clicking the mouse. From the
“ASCII file internal format” combo box, select “X-Y-Z (DTM)” option. Click on the “Draw
Histogram ->” button.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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If you know the number of the row and the column elements of the pointcloud, then write
them to the “Width” and “Height” areas. Otherwise, select one of the appropriate dimension
from the small text box.
•
Carefully inspect the data file and understand the NODATA definition which is Z=-999.00 in
our example here. Open the “NO_DATA” tab and apply the nodata value appropriately.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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Open the “stretching” tab. Apply those values. These are linear contract stretch parameters
to be used only for display purposes, not in the computation.
•
Click the “Save as XX2” button. Thus, the conversion procedure for the X-Y-Z pointcloud
file is finished. The conversion parameters can be seen in the file
“LI_DMC_1M_DSM_ACX_CROPPED.asc.xxx_ConvInfo.txt”.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
SURFACE MATCHING
Step 1: Co-registration
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Load both of the files by clicking the File/Open XX2 File menu button.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
•
First, click the “select all” button
of “4strips_esri_1m.asc.xx2” file (template surface,
fixed) then, click the “select all” button of “LI_DMC_1M_DSM_ACX_CROPPED.asc.xx2” file
(search surface, to be transformed).
•
Click the Registration/Pairwise Registration [Ls 3D Surface Matching] menu button. Select
“DSM & DTM data (meter)” from the “Data type” combo box.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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Click on “3Dbox” tab, and change the min Dim-X, Y, and Z parameters to 5.0 meters.
Search surface has a 1 meters resolution. Thus, min Dim-X, Y, and Z parameters should be
factor 3-5 of the point spacing of the search surface.
•
Click on “Pairwise registration - THIS” button. The algorithm should run for a while and an
output file is posted to the screen.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
Step 2: Transformation
•
The estimated transformation parameters are written in
“LI_DMC_1M_DSM_ACX_CROPPED.asc.xx2.trf” file. To apply the transformation
parameters, click on File/ Transform and Save as Binary XX2 menu item. Select the
“LI_DMC_1M_DSM_ACX_CROPPED.asc.xx2” and click on “Save” button.
If the task is only transforming the search surface to the domain of the template surface, user
should stop the procedure at the end of the Step 2. However, in many cases to understand the
quality of the fit between the template and search surfaces is meaningful. This is especially valid
for the quality assessment and change detection tasks. Step 3 provides this information.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
Step 3: Comparison
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Registration/Pairwise Registration [Ls 3D Surface Matching] menu button. Make below
settings.
We set the robust re-weighting factor to a very large number. This leads not to exclude any
observation from the process.
We set the weights of the translation and the rotation elements to very large numbers. Thus, their
value will not vary during the computation.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
Set very large box sizes. If you see black blocks in the final residual graphs (see the next process)
increase the box sizes further.
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Run the matching by clicking on “Pairwise registration - THIS” button. The process takes
some minutes depending on the file sizes. After the computation an output file will be
displayed.
Click on the File / Generate Colour Residual Map menu item.
Select “z_LS3D_rig_TriP_residuals1001.txt” file.
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LS3D Documentation, ©2008, P+F - ETH Zurich
by Dr. Devrim Akca
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Make the below settings. Put minus plus of the 3 times of the sigma value computed in the
output file. Click on the “Process” button.
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The graphical and text output files are in:
z_LS3D_rig_TriP_residuals1001.txt__0_imgDIS.bmp
z_LS3D_rig_TriP_residuals1001.txt__0_imgDIS_lej.bmp
z_LS3D_rig_TriP_residuals1001.txt__0_statis.txt
files.
Colours represent the magnitude of the final left over Euclidean distances between the
template and the search surfaces.
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