GPS coordinate issue
kentman
Global Mapper UserTrusted User
I have been recording my journeys with GM linked by Bluetooth GPS receiver. The base map I'm using is in British National Grid (BNG) and when I save the tracklog and then view the vertices coordinates are in BNG format but the one I did yesterday is in Lat/Lon, which makes it difficult to map in MapInfo when I save the information to a text file!
Why do the coordinates change like this - I want it to stay as BNG. Nothing has changed since the last save of the workspace and if I set the projection of the layer to BNG the line completely moves off it's recorded position!
Any ideas?
Why do the coordinates change like this - I want it to stay as BNG. Nothing has changed since the last save of the workspace and if I set the projection of the layer to BNG the line completely moves off it's recorded position!
Any ideas?
Comments
-
All exports should occur in the projection set on the Projection tab of the Configuration dialog. Make sure you have that set to British Grid. Don't change the projection of a layer on the Projection tab of the Options dialog for the layer, that will change the actual position of the data on the earth and its rarely needed.
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
global_mapper wrote: »All exports should occur in the projection set on the Projection tab of the Configuration dialog.
So it seems that I have to make sure that the projection is confirmed as BNG, even though it tells me its in BNG, to get the vertices as BNG!
I don't understand - can you shed any light on the matter?
Kent -
Kent,
The vertices will always come in from the GPS as lat/lon WGS84 and will be recorded as that by GM. If you export to a new file the export should be done in whatever projection that you have set on the Projection tab of the Configuration dialog. So if you set that to BNG then export to a new file the coordinates should be convert to and saved in BNG (assuming you don't export to a format that requires lat/lon, like GPX or KML).
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Mike, OK I need to qualify what I mean: when the track has been recorded and I select it with the info button and then select 'Vertices' the vertices show as Lat/Lon but, if I've gone into the Projection and confirmed BNG before recording the track they are show as BNG coordinates in the 'Vertices' list - what I do here is to copy them to the clipboard so I can bring them into MapInfo and do some analysis. If I export 'All Vector' as mif/mid it only gives me the tracklog line with no attributes except the start and end points - no good to me.
I hope that explains it more clearly. -
The Vertices dialog will always display vertices in native projection of the layer they are in, which will be lat/lon WGS84. If you use GPS->Save Tracklog and choose to save the tracklog it will by default save it to a layer as lat/lon/WGS84 coordinates, but if you choose a different layer (like perhaps a new layer) when saving the tracklog you can save it in a layer with a different native projection so you can view the coordinates in that projection.
I would expect all points to be stored when you export to a file except any that were removed due to simplification, but that should only be points that don't significantly contribute to the shape of the line. Can you try after saving the tracklog and see if you get the same results?
Thanks,
Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com -
Thanks Mike, it is indeed the case how you have explained it so when I do save the tracklog as a new layer I get the vertices as BNG. Just my misunderstanding of the process - thanks for the clarification.
On the issue of points being saved: if I export layer as MapInfo TAB all I get in MapInfo is a line but if exported as mid/mif I get the points - I think this is to do with the TAB format and how MI reads it. Strangely, if the exported TAB file is opened in Quantum it sees the points and line whereas MI doesn't!
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