# Cartesian co-ordinate system with set 0,0 point?

This is for visualization in construction project planning:

I would like to set a 0,0 point and angle relative to North for an X,Y (and possibly Z) Cartesian co-ordinate system that will then show the cursor position in feet (or meters) relative to the 0,0 point.

It would behave like the co-ordinate window showing Lat./Long. but in feet instead, using the projection system of the layer, or project.

A specific example: I would like to set the corner of a barn as 0,0 and then know where the cursor is in X,Y feet (aligned to the property's road frontage) from that point as I move it around the map.

• It sounds to me like you're talking about a local coordinate system.. you should be able to create one for your project based on your existing coordinate system and modify parameters like false easting and false northing to make your local origin 0,0. What coordinate system is your data currently in? – Michael Stimson Sep 14 '16 at 0:47
• Is the coordinate system determined by the projection? It's EPSG:3857. I guess I've jumped into the deep end of the pool. QGIS seemed so easy to get my maps assembled. But I need to read up on all this. – erkq Sep 14 '16 at 2:26
• The first thing you want to do is find a good projection in metres (or feet) with WGS84 datum, UTM is my go-to so long as your data isn't many degrees wide, which it sounds like it isn't. Obtain your coordinates for the 0,0 point in this spatial reference then modify the false east/north of the UTM spatial reference, set your canvas to the modified spatial reference (enable project-on-the-fly) and you should be now in local coordinates. – Michael Stimson Sep 14 '16 at 3:51
• To expand on @MichaelMiles-Stimson suggestion, you would use the lat,lon values of the 0,0 location to set the latitude of origin and central meridian of a modified UTM/transverse Mercator. False easting/northing should be set to zero. However, this will not align the coordinate system with the road frontage. If you used oblique Mercator, you could also add an azimuth value to rotate the coordinate system (maybe)--OM has an odd implementation in proj.4 (used in QGIS). – mkennedy Sep 14 '16 at 20:14