Coordinates loaded into wrong location and scale

Hello

Apologies if this is an obvious question - I am very new to Global Mapper but I haven't found an answer to this issue after a few hours of searching.

I am trying to load a .txt file with several (about 70) coordinates into Global Mapper v18.1, having obtained the coords with the Google Geocoding API from addresses. These are decimal coords seperated by tabs, e.g.

LATITUDE LONGITUDE
50.086534 -5.3134111
50.0887322 -5.3106832
50.0838962 -5.3148797
...etc.

Since these were from Google I have assumed a Mercator projection with the datum from EPSG 3857. When I try searching any of these coordinates in Google Maps individually there are no issues locating the buildings, so I know the data is correct.

However when I load just these ~70 coordinates into Global Mapper the scale is way too small, with the data points being about 0.001m away from eachother when they should be more like 10-20m apart (residential housing scale).
- Why is this data being scaled down like that, and how do I fix it?

I have also been trying to load these data points onto an OS map with boundary lines for the town, which uses a different projection/datum (British Grid, OSGB36 (BEST TRANSFORM)). When I do this the points end up about 150 km west of where they should be on the map, even if I convert these data points to the same projection/datum as the OS map (assuming I have done that correctly).
- How can I get these points to match up correctly with the boundary line map?


This is all on Windows 7.


Many thanks in advance

Zach

Answers

  • JeffH@BMGJeffH@BMG Global Mapper Developer Posts: 267Trusted User
    Hi Zach,

    The problem that you're having is that by choosing a Mercator projection using meter units, you're telling Global Mapper that your coordinates are meters, when they're really in degrees. You should be using a Geographic projection, with the datum of your choice.

    Cheers,

    ~Jeff
Sign In or Register to comment.