# Formula for converting SWEREF99 to WGS84?

I have a few hundred rows of data with sweref99 coordinates that I want to plot using Fusion Tables on Google Drive.

What formula can I use to convert the two columns of Sweref99 x and y coordinates?

All my Google results so far just makes me end up at converters, not any formulas, forcing me to manually convert every row.

• SWEREF99 and WGS84 are often considered equivalent so you just have to find a robust ellipsoidal transverse Mercator algorithm. One place could be IOGP (EPSG) GN 7-2 pdf. Disclosure: I'm on the subcommittee that maintains it. Apr 29, 2015 at 21:47
• Is there maybe a way to make this algorithm more approachable? I'm not even sure if "robust" has a specific meaning in this context or if you just mean "good", and I can't find the phrase "ellipsoidal transverse Mercator algorithm" anywhere in the pdf. Aug 31, 2015 at 17:50
• Yes, robust means good where good means 'supports an adequate range of longitudes at mid- to -high latitudes. Some transverse Mercator algorithms use series expansions in the calculations. if the series doesn't have enough terms, longitude calcs on inverse (from xy) start to not work at 8-9 degrees--less at higher latitudes. Aug 31, 2015 at 17:54

You can use the Proj4 converter: http://trac.osgeo.org/proj/ Yes, it is a converter but you can convert bulk coordinates.

Create a simple text file (let's say `sweref99.txt`) with the coordinates, e.g.

``````606905.22 6970515.93
635765.54 7223101.41
``````

In order to convert all coordinates from this file the command is like this:

``````cs2cs +init=epsg:3006 +no_defs +to +init=epsg:4326 +no_defs sweref99.txt
``````

You just have to use the correct EPSG code for SWEREF99, this I don't know which one. You should find it here: Spatial Reference or epsg.io

• from = spatialreference.org/ref/epsg/3006 (epsg projection 3006 - sweref99 tm) to = spatialreference.org/ref/epsg/wgs-84 (obvious one) Apr 29, 2015 at 20:33
• Thanks for the answer, sorry for being the slowest responder ever. I tried doing this and got a (fairly encouraging) error. "projection initialization failure. cause: no options found in 'init' file. program abnormally terminated." Do you know what might fix the problem? I've just followed the readme provided in the download and your and r.pankevicius instructions. Aug 31, 2015 at 17:39
• You must define an environment variable called `PROJ_LIB`. As value put the folder name where the projection file `epsg` is stored Aug 31, 2015 at 20:28
• That's what I do to get this error. I get another error message when i assign another value to PROJ_LIB: "projection initialization failure. cause: no system list, errno: 2", so I must be doing something right... Any ideas? Sep 2, 2015 at 9:30
• Please open a new question with tag `proj.4` where you describe the problem. Surely you will get an answer. Sep 2, 2015 at 9:33