Frequently Asked Questions

Input data

How to create CARS compatible ROI input data with OTB ?

CARS supports the ROI products extracts done with the otbcli_ExtractROI OTB application (raster + geometric model).

  • First, retrieve the coordinates of the desired extract on the first image (lets call it img1.jp2), under the form startx, starty, sizex, sizey (in pixels).

  • Perform the extraction of the first image with:

$ otbcli_ExtractROI -in img1.jp2 -out img1_xt.tif uint16 -startx startx -starty starty -sizex sizex -sizey sizey
  • Extract the same zone on the second image (for example img2.jp2), the -mode fit application option has to be used:

$ otbcli_ExtractROI -in img2.jp2 -out img2_xt.tif uint16 -mode fit img1_xt.tif

The application will automatically look for the zone corresponding to img1_xt.tif within img2.jp2.

It is possible to use the -elev.dem srtm/ option to use the DEM during this search in order to be more accurate.

It is to be noted that the option also exists. It accepts a vector file (for example a shapefile or a kml) which enables the image extraction from a footprint.

How to generate input images in epipolar geometry from grids ?

To generate the images in epipolar geometry from the grids computed by cars and the original images, one can refer to the Orfeo Toolbox documentation here .

Output data

How to generate output files overview ?

Considering bulky files, it can be recommended to generate an overview file with GDAL before opening it with QGIS:

$ gdaladdo -ro -r average dsm.tif 2 4 8 16 32 64