# 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. – mkennedy Apr 29 '15 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. – Henrik Aug 31 '15 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. – mkennedy Aug 31 '15 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) – Remigijus Pankevičius Apr 29 '15 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. – Henrik Aug 31 '15 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 – Wernfried Domscheit Aug 31 '15 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? – Henrik Sep 2 '15 at 9:30
• Please open a new question with tag `proj.4` where you describe the problem. Surely you will get an answer. – Wernfried Domscheit Sep 2 '15 at 9:33