# How can I transform Real-time Local position system coordinates into GPS/WGS84?

I have a local coordinate system built with Ubisense sensors and tags (it is a real-time locating system used to automatically identify and track the location of objects or people). The local coordinate system is simply a cartesian coordinate system, which I can define the origin and axies at will except the rule that x-y panel must be horizontal, thus the z axis is vertical. After setting up the system, I can get coordinates of tags in the contained area where the sensors can get signals emitted from the tags and locate the tags. Now, I have the problem to convert the (x,y,z) coordinates into global system coordinates.

I made a model myself which took the origin of local coordinate system as a reference point and calculate the difference of other points in lat and lon to make the transformation. However, I guess there must be more standard and accurate way to deal with such problem. Since I am a noob in this field, I did google something and read some pages. However, there is rarely content relevant with this topic(much I found is from some standard to another, however is not a standard coordinate system, it is cartesian but not geocentric). Anyone can give any hints or suggestions for this problem? Your help or attention to this question will be much appreciated.

## 1 Answer

I think you can solve your problem the same way as I suggested here:

Using customized Coordinate System in ArcGIS Desktop?

A local Transverse Mercator CRS at the point of your origin should work. Transformations can be done with cs2cs from the GDAL package.

• Thx. I think this is what I need. However, I know how to do the projection in commandline but dont know how to do something like:+proj=tmerc +lat_0=51.4 +lon_0=7 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +units=m +no_defs in plain code.I know how to initialize some OGRSpatialReference objects for my source and target CRS and a transformation object. But I still dont know how to add the lon_0, lat_0 , angles of oblique to my source CRS. – Derek Feb 7 '14 at 10:16
• I can't help you on coding, but using a proj string instead of EPSG codes should be possible in Python and C. I think this should be put as another question. – AndreJ Feb 7 '14 at 10:33
• The lat_0 and lon_0 are the coordinates of your local CRS origin. You have to explore these with a GPS or from other maps. The angle you have to calculate from the coordinates of two known points on your local X-axis. – AndreJ Feb 7 '14 at 12:08