2

Say I have the coordinates: N: 5413457.7 E: 1528677.3

If I were to add 10 to the northing value would that make the new coordinates point 10 meters north of the original point?

  • How are they in a table? is it Text N: 5413457.7 E: 1528677.3 or Northings field and Eastings field? I would use field calculator but need to know if the text needs to be broken down and reassembled or if it's just adding to numbers. – Michael Stimson Feb 3 '15 at 0:36
  • @MichaelMiles-Stimson Sorry, I don't understand your question. I'm very new to dealing with coordinates, but I am storing simply a North and South value in an application I'm developing. I have the functionality built in to allow easy conversion between ECEF, NZTM and WGS84. What I need to be able to do is "move" a coordinate north by 10 meters and east by 3 (That is north/east as in north/east that would be on a compass). – Adrian773 Feb 3 '15 at 0:39
  • Yes, just add 10 to the north, 3 to the east and done! But that's not true north, if you want that kind of refinement the question is much more complex. What software are you using? I assumed ArcGis (in the absence of any other) but it sounds like you're developing a program? is it .net, Java.... Geographic coordinates however you can't just add 10 and 3. – Michael Stimson Feb 3 '15 at 0:44
  • Awesome, want to put that as the answer and I'll accept? C# application which I'm using to produce .kml files for Google earth (among other things). I need to be able to calculate the change of distance so that I can recalculate the start/end positions of a pole that is on a lean. – Adrian773 Feb 3 '15 at 0:48
  • The true answer is much bigger than you think. Roughly you can add/subtract values and get within a few centimetres, I have done this before for AGD66 to AGD84 which was close enough at the time. Mostly GIS folk use software like ArcGis or GDAL/OGR to do this sort of calculation for them - projection instead of adjustment. Proj.4 trac.osgeo.org/proj is an open source projection utility that you might want to consider using if more accuracy is required; this will also allow you to project to WGS84/Geographic which is more than just adjusting numbers. – Michael Stimson Feb 3 '15 at 0:53
4

Yes, but to explain why:

I can tell that you have projected coordinates (as I assume you're in New Zealand) the numbers are quite large, much bigger than -180 to 180, which is probably New Zealand Transverse Mercator 2000:

Projection type:Transverse Mercator 
Reference ellipsoid:GRS80
Datum:NZGD2000
Origin latitude:0° 00' 00" South
Origin longitude / central meridan:173° 00' 00" East
False Northing:10,000,000 metres North
False Easting:1,600,000 metres 
EastCentral meridian scale factor:0.9996 - See more at: 

Which is in metres, so you can add 10 to go 10 metres north... approximately. Zones are slightly banana shaped so it's not a true north but roundabout. You can expect to be within a few centimetres of the correct location; the larger the displacement and the further from the centre of the zone the more you are likely to be off.

To get a more accurate figure use software like GDAL/OGR (OGR is for points, GDAL is for raster but they're distributed in the same package); GDAL uses the PROJ.4 library for coordinate transformation. This is open source software so is free to use. It's been a while since I've done OGR and I think it goes a little like this:

OGRpoint myPoint = new OGRPoint(Xcoord,Ycoord);
OGRSpatialReference fromSR = new OGRSpatialReference();
fromSR.importFromEPSG(2193); // NZTM is 2193, WGS84 UTM 59 south is 32759
OGRSpatialReference toSR = new OGRSpatialReference();
toSR.importFromEPSG(32759);
OGRGeometry myGeom = (OGRGeometry) myPoint;
myGeom.assignSpatialReference(fromSR); // assign the spatial reference
myGeom.transformTo(toSR); // convert to the 'to' spatial reference
myPoint = (OGRpoint) myGeom;
outX = myPoint.getX();
outY = myPoint.getY();

This is more accurate than simply adjusting the X and Y... WGS84/Geographic is EPSG:4326.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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