If you have any experience in this subject...or if you can guide me to good reading material would be glad. Not familier with this yet.
Comparing between a good quality georeferenced orthophoto and a historical aerial photo, seems to be a high-oblique photograph. Covergages are different, they partly overlap.The times taken are different, historical one is laiden with long shadows. Both have 3 bands each; RGB. Historical photo, RGB values are quite close (not the same though!). It also has bad data: as white strips plus white patches of data (not pure white; data are there, DN is higher, so WHITER). Fiducial marks are there, but no information on the geolocations. Tried to register regions of interest of the historical photo to the orthophoto using known locations, but everytime, ended up having expanded objects in the historical photograph, eventhough locations are quite closer to the orthophoto.
Is georeferencing and orthorectifying required? couldn't this be achieved only with registering?
Is it possible to use this kind of an aerial image for a change detection for at least planly visible areas?
Thanks
Hi Nilupul,
Aerial photographs need to be orthorectified and georeferenced. Orthorectification is about geometrically warping the image so that it becomes planimetrically accurate, and not a perspective image, which is what a photograph is. If you're using ArcMap, orthorectification and georeferencing are generally done together by establishing control points, minimizing position error measured by Root Mean Square Error (RMSE), and selecting a mathematical model for how much warping to allow in the image (i.e., a polynomial model). Have a look at:
http://resources.arcgis.com/en/help/main/10.2/index.html#/Fundamentals_of_orthorectifying_a_raster_dataset/009t000000ms000000/
I'm sure this is possible in open-source GIS like GRASS, SAGA, or QGIS, just haven't done it there myself.
Cheers, hope this helps,
P
Hi Nilupul,
Paolo has spelled out what needs to be done on the technical side. Nothing to add there.
What you may need to consider as well, however, is how much the historic aerial photo can actually tell you. The resolution will be determined by the nature of the camera, the film and the photographic aerial platform used at the time. These parameters change over time. Some of that is discussed in this paper: https://www.researchgate.net/publication/272312418
Cheers
Dirk
Article Interpreting World War II Intelligence Data for Cultural Her...
Thank you Dr. Spennemann.
yes, the different properties of the two photographs seem to affect what I am seeing on the ground, to a very large extent. Thank you for leading me to the article.
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