Forum: General Topics

Hi,

I am having trouble calibrating a map. It's a nautical chart that I know is accurate because I have used it in other mapping programs. The coordinates are clearly marked on the map but when I enter them into the map organiser there is a descrepancy of a few kilometres.

I have also been using google earth to get my co-ordinates but with now luck

For example how would I enter 36o08'.54 south (where "o" is the degree sign). Because I have been entering it as -36.0854. Once I fill in all the coordinates into map organiser and scroll around the map I may get a number like 174.8562E, but if I scroll around google earth the decimal numbers after 174 will only go up to 60 and then it would go to 175.

I am really stuck and I've read all the other forums but they haven't help.

If I create a map from the tile server, it is calibrated correctly and tracks perfectly on my phone (even though the co-ordinates in the map organiser don't match google earth?)

Please help!!

Hi Jimmy,

Google Earth should work fine for working out the coordinates of a place but you need to make sure that you enter them into the Map Organiser in Decimal degrees, rather than Degrees, Minutes and Seconds as it looks like you might have been. To convert from DMS to Decimal Degreees you can use the following formula:

Decimal Degrees = D+M/60+S/3600

If the coordinate is South, or West, then the plus signs should be changed to minuses, ie:

-D-M/60-S/3600

So your example of 36D08M54S South (I assume the 08'.54 is actually 8 minutes 54 seconds rather than 8.54 minutes?) would be:
-36-8/60-54/3600 = -36.148333

Incidentally, in the Google Earth Tools/Options/3D View settings there is an option to display the coordinates in Decimal Degrees, avoiding the need for the above conversion.

There is a second potential problem though in using a nautical chart since it is possibly not in the correct projection for use in the Map Organiser (it needs to be either Rectangular or Mercator). This will result in a slight variance being displayed on the map from the actual location, though if you're lucky the exact difference might be fairly small.

Hope this helps!

Cheers,
Stephen