Peculiar inaccuracy in position of markers

Topics: Help
May 17, 2012 at 12:08 PM

Hi all - I have created some markers using the following vb2010 code


'loop around inserting points
coordsys = TDPG.GeoCoordConversion.CoordinateSystems.OSGB36 units = TDPG.GeoCoordConversion.AngleUnit.Degrees coords.Easting = currnodex coords.Northing = currnodey latlng = TDPG.GeoCoordConversion.GridReference.ChangeToPolarGeo(coords) temp.Lat = latlng.Lat temp.Lng = latlng.lon

Dim r1 As New GMap.NET.WindowsForms.GMapRoute(pl1, "route1")
Dim o1 As New GMap.NET.WindowsForms.GMapOverlay(Me.GMapControl1, "routeoverlay")
r1.Stroke.Color = Color.Red
r1.Stroke.Width = 1

the overlay gets drawn but is not accurate on the map - it doesn't matter which map provider I use - I've tried Yahoo, Bing and OpenStreet.

Initially, I thought there was a slight inaccuracy in the 3rd party tool I was using to convert from Eastings/Northings to Lat/Long but I exported the converted values and imported them into MapInfo and they are correct. So I don't understand why GMap isn't plotting them at the same positions as MapInfo (on OS 1:10K raster mapping)

Any ideas anyone?



May 17, 2012 at 1:02 PM

can you try to do the same conversion using DotSpatial?

May 17, 2012 at 1:08 PM

Interestingly, if I plot my converted co-ordinates into Google Earth, they are also misplaced, so the fault can't be in GMaps or the conversion.

I wonder if the base mapping is not as accurate as the OS 1:10K I am comparing it against. I recall that the OS tidied up their stuff in the Positional Accuracy Improvement programme. But I find this hard to believe because this would mean that all Objects plotted on web-mapping would be affected.