Production of orthophotos of the Vällen and Länna areas and studies of production lines for CIR photos of large areas. This was done in cooperation with Sören Holm. Production of orthophotos of the Vällen and Länna areas in Uppland County from black and white paper copies from the 1940’s. The difference between orthogonal projection (that orthophotos has) and central projection (that aerial photos has) is that the orthophoto has all its points imaged from straight above while the aerial photo has a greater distortion the further from the centre you look.
The production line for the making of digital orthophotos is done in many steps; orientation of the photos, relative orientation between photos, absolute orientation compared to the Swedish RT90 coordinates, recalculation to the orthogonal projection (rectification) colour balancing and cutting of maps.
The price for orthophotos as described above is about 2,000 SEK per 5×5 km square.
Orthophotos is advantageous as a background for other data and also contains much complementary information which gives a better over all impression. It is possible to interpret some simpler object types and to digitalize these against the orthophoto.
Here are some examples from digital orthophotos that show the landscape from 1941, 1945 and 1999:
|Produced from scanned paper copies of aerial photos from 1941. The negatives are burnt and the paper copies are used for the production of the first 5×5 km map with orthophoto background. The marks were used to create orthophoto mosaics.||Scanned paper copy of aerial photo from 1945.||CIR-photo from 1999
scanned directly from the negative.