I've been using QGis for few weeks now. Although this site always came very helpful, I can't find solution to my recent problem:

I have few points, and know their coordinates in "WGS-84" and "ISN-93" systems. Those points also have specified coordinates in "Local" system.

The problem is that there are also few points that only have "Local" coordinates, and I would like to find their "ISN-93" coordinates.

How can I do it?

*for example:

point1 ISN93 (685320.253,420614.733) Local (-3537.239,2284.487)

point2 ISN93 (685841.253,420586.536) Local (-3016.528,2248.842)

point3 ISN93 (?,?) Local (-5187.996,2584.508)

I was trying to use simple geometry, but when I measure distance between points, ISN93 system gives slightly different lengths than Local (difference vary between lengths to up to 0,01% of its value), so it's no use.

  • Do you have access to the surveyor or other person who created the local grid? Sometimes they also have the transformation values to convert to a more well-known coordinate reference system. Otherwise, you might have to use something like georeferencing, but for vector data.
    – mkennedy
    Commented Jul 10, 2015 at 16:20

1 Answer 1


A very simple brute force approach:

  1. take the first points coordinates and convert them from ISN93 / Lambert 1993 to WGS84 degrees using cs2cs in the OSGEO4W shell

    cs2cs +init=epsg:3057 +to +init=epsg:4326 -f "%%.8f" <ISN93.txt >WGS84.txt

  2. build a local omerc CRS on that point, with the "local coordinates" as false Easting and Northing

  3. convert the point coordinates into this custom CRS

    cs2cs +init=epsg:3057 +to +proj=omerc +lonc=-15.1778877053125 +lat_0=64.2376322211738 +alpha=0.01 +gamma=0 +k=1.0 +x_0=-3537.239 +y_0=2284.487 +datum=WGS84 +units=m +no_defs -f "%%.8f" <ISN93.txt >local.txt

  4. calculate the offset X and Y in meters for the second point

  5. play with +alpha and +k values to minimize the offsets

This way I get with an offset of 2mm:

+proj=omerc +lonc=-15.1778877053125 +lat_0=64.2376322211738 +alpha=2.646 +gamma=0 +k=1.00032 +x_0=-3537.239 +y_0=2284.487 +datum=WGS84 +units=m +no_defs

I assume your coordinates are in East-North order, and you don't have to care about tectonic moves between ISN93 and WGS84. On an Openstreetmap background, your local grid looks like this:

enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.