👍 logical and clear thanks Marc MILLAS Senior Architect +33607850334 www.mokadb.com
On Thu, Feb 9, 2023 at 6:16 PM chris hermansen <[email protected]> wrote: > Mark and list; > > On Thu, Feb 9, 2023 at 8:24 AM Marc Millas via QGIS-User < > [email protected]> wrote: > >> Hello, >> >> I got an autocad dxf file describing objects in Djibouti. >> no pb to load it in qgis as a vector layer. >> but... the srid seems to be 0 and QGIS ask for a valid ref >> as the data looks x,y, I did try epsg 32638, which is standard in >> Djibouti. >> loads fine... but the objects are around 200km west of where they should >> be. >> >> any idea ? >> >> Perhaps your dxf data is not georeferenced. It may be in rectangular > coordinates (x, y) representing metres from some origin point that makes > sense when thinking of it as a drawing (like the centre of the drawing or > the southwest corner or a nearby landmark). > > Therefore when you assign a projection to it, its origin point will be at > the origin of the projection. In your case using EPSG 32638, that is UTM > zone 38N whose centre coordinates are 500000 4649776 (see > https://epsg.io/32638). > > The origin point of your drawing will be in that coordinate system; (0,0) > will be 500000 metres west of 45° east longitude and on the equator; in > other words, 40.511256° east longitude and 0° latitude. > > The latitude and longitude of Djibouti City is 11.572076, 43.145645 (see > https://www.latlong.net/place/djibouti-city-djibouti-24884.html). You > can see that your origin point (0,0) in UTM zone 38M is 2.634389° west and > 11.572076° south of Djibouti City. > > Working back to UTM coordinates, in UTM zone 38N Djibouti City is > 297791.1138793365 east and 1279891.9276488272 north (see > https://epsg.io/transform#s_srs=4326&t_srs=32638&x=43.1456450&y=11.5720760 > ) > > If your DXF data coordinates - say the centre of the drawing file - aren't > somewhere around (297791,1279892) then you need to transform your data as > you import it (or afterward). > > Please read these articles > > https://opengislab.com/blog/tag/DWG+DXF+QGIS > https://gis.stackexchange.com/questions/22691/georeferencing-dxf-using-qgis > > https://www.mkrgeo-blog.com/good-solution-to-georeferencing-the-autocad-dwg-drawing-in-qgis-3x/ > > which will provide you with some ideas and more background info. > > -- > Chris Hermansen · clhermansen "at" gmail "dot" com > > C'est ma façon de parler. >
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