Aerial photography [BD ORTHO® History — IGN-F] — Department of Calvados — 1991

BD ORTHO® History of 1991 produced by the IGN on the entire Department of Calvados. The product BD ORTHO® History 1991 is a collection of digital mosaics of ancient panchromatic orthophotographs (grey levels) rectified in the projection adapted to the departmental territory (Calvados). BD ORTHO® History of 1991 is freely distributed under an open license thanks to the financial support of the Department of Calvados. The ORTHO® Historical BD consists of digital images (without covering or overloading) and georeferencing indications. The informational content allows local use up to 1: 2,000 to develop the territory. The 1991 ORTHO® BD offers many advantages: — spatial planning: land tenure, land use and new communication channels; — environment: coastal and forest observatory, bocage management; — communication: visualisation of the evolution of the territory. The original files distributed by the Department of Calvados under Open License are: — in legal projection Lambert 93 NTF (Paris)/Lambert zone I (EPSG: 2154); — in Geotif format per slab of 2 km x 2 km; — with a resolution of one pixel = 50 cm; — compressed as a zip archive. Below you will find links to access “multi-party” files for free download. To unzip “multi-parts” files: — Make sure you have downloaded all the parts: 001, 002, 003... — Put all parts in the same directory — Click on file 001 (e.g. tif_1991.zip.001). No need to click 002, 003, 004... Open file.001 opens all other parts of the archive If you have an error there is a good chance that one of your files was only partially downloaded. In order to facilitate the use of these orthophotos, the files proposed here are in GeoPackage OGC format in lambert 93. **Collection context** The number of photographs needed to cover a department is important, these photographs show strong differences in sunshine, colourful appearance, landscape, object behaviour (careers, sands, water surfaces,...) and sometimes seasonal. In practice, the process seeks to correct each image of the internal lighting and color effects associated with sunshine. All images must also be homogenised. For each image an illumination correction (hot-spot and vignettage) is applied. Once this correction has been applied, the images are broadly equalised throughout the construction site. It may be added that on some shots, the use of short focal points or these wide-field cameras has generated important and more difficult to correct vinttage effects (difference in illumination between center and edge of the image). **Collection method** The Geopakage was produced from the GDAL library: * gdalbuildvrt D:\4_Ortho_1991\1991.vrt -addalpha -srcnodata 255 -hidenodata D:\4_Ortho_1991\data\*.TIF * gdalwarp D:\4_Ortho_1991\1991.vrt D:\4_Ortho_1991\1991.gpkg -t_srs EPSG:2154 -r cubic -of gpkg * gdaladdo -r cubic D:\4_Ortho_1991\1991.gpkg 4 16 64 256 For more information, see [the metadata on the Isogeo catalog](https://open.isogeo.com/s/434296189d794266a04a8678e256f0c4/HiLeps3y1qrSx6aTDmKyp0spGPix0/r/22cf775d39cf430a8287b1dacb91168a).