Hi Johannes
> However, as I want to automatize the step of rectifying/georeferencing I >> am looking for a way to autodetect these six points in the image. I am >> thinking of tools like pattern/face recognition that are able to >> autodetect objects (e.g. eyes, points etc.) and extract their position >> (coordinates) within that image. I assume these coordinates together >> with their "true" position could then be used for rectifying the picture >> using e.g. i.rectify. >> >> Has anyone done this or a similar exercise before and can recommend >> tools and approaches to auto-detect GCP from an image? >> > > For a similar purpose, to automatize image to image registration, I have used the library OTB toolbox(https://www.orfeo-toolbox.org/) along with GRASS GIS. OTB has a module called homologous point extraction which uses algorithms like SIFT and SURF. https://www.orfeo-toolbox.org//Applications/HomologousPointsExtraction.html After getting the gcp's, I used grass plugin m.gcp.filter to filter out the outliers, followed by i.rectify. On a GRASS environment, following is what I used - representative code: > #GCP extraction using OTBcli_homologous points > otbcli_HomologousPointsExtraction -in1 input_b1.tif -band1 1 -in2 > reference_b1.tif -band2 1 -algorithm sift -mode full -out OUTB1.txt > # Making the text file GRASS compatible > awk '{$5="1\t"$5}1' ${MYTMPDIR}/OUTB1.txt > ${MYTMPDIR}/OUTB1.txt > # importing the input TIFF files > r.in.gdal input=${y}_b1.tif output=${i}_b1 memory=${MEMORY} #Moving the POINTS file to the GRASS group folder > mv ${MYTMPDIR}/OUTB1.txt ${GRASSLOC}/group/${i}/POINTS > #GCP filtering > m.gcp.filter group=${i} order=1 threshold=500 -b > i.rectify -a group=${i} extension=_rectified order=1 method=nearest --o > In this paper (http://www.mdpi.com/2072-4292/8/3/169/htm) , the steps are explained and main codes are provided in appendix. Here is a good link on SIFT, I guess it is more apt for your case with digital photographs. In the above case, we tried on satellite data. http://www.aishack.in/tutorials/sift-scale-invariant-feature-transform-introduction/ Hope this helps!! Sajid
_______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
