New answers tagged

1

If you have National Grid coordinates with trailing letters, you can not use these in ogr2ogr. The ngconverter linked in the other answer will be the best solution. It will output coordinates in EPSG:27700. If you have numerical coordinates, EPSG:27700 will work in ogr2ogr, as pointed out by @iant.


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Something like: ogr2ogr -f XXX -s_srs epsg:27700 -t_srs epsg:4326 out.xxx in.shp The ogr2ogr manual page explains all the options.


0

This script converts lat/lon coordinates to mercator coordinates using mercator scale r = 6378137; scale = cos(lat * pi / 180.0); x = scale * lon * pi * r / 180; y = scale * r * log( tan((90+lat) * pi / 360) );


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As a first guess, you can create a custom transverse mercator projection on one of you coresponding points. Preferably the one closest to the DXF origin: +proj=tmerc +lat_0=41.045452 +lon_0=28.895929 +k=1 +x_0=1.03521 +y_0=-6.34918 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs lon_0 and lat_0 are the degree coordinates in WGS84, and x_0 and y_0 ...


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Have a look at How to georeference a vector layer with control points?, in particular the answer concerning the Vector Bender plugin for QGIS. Watch the video and try the plugin, report back if you encounter any issues.


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I think you have to carry out three transformations, wich are all affine transformations: scale, rotate and translate. I suggest reading about affine transformation on wikipedia: https://en.wikipedia.org/wiki/Affine_transformation If you basically can carry out an affine transformation, then this might help you to determine the correct parameters: http://...


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The plugin in the accepted answer is not available anymore. The Affine Transformations is available and is very useful. With this plugin you can create a formula. In the screenshot I shifted all cells with 17.396 (meters) to the north.


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In ArcGIS you should load the CAD data first and use the Georeferencing toolbar to establish world file coordinates before converting to a shapefile as explained in the Georeferencing CAD datasets help. There are several related help links in this section that explain how you can apply a transformation, but that generally means that the local coordinates ...


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thanks for your answers. I think the problem is the +towgs84 parameter. The 23030 layer is stored in a PostGIS 1.4.2 database and it hasn't +towgs84 in proj4text column spatial_ref_sys table: +proj=utm +zone=30 +ellps=intl +units=m +no_defs Could be this the problem? Greetings.


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How big is the shift? If it is around 100m it might be due to datum transformation as another reference ellipsoid is used in both. If this is the case you need the transformation parameters for ED 50 towards GRS80 in Qgis. The other programs might have this already and applying it therefore correctly. You can also reproject on of them using the also ...



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