Map GPS Coordinates - GPS Map Coordinates ... - Global Mapper

Global Mapper User's Manual
Use the Projection pull-down menu to select the projection you wish to view the currently loaded data in. The
Geographic projection is really the absence of a projection. It is just a linear mapping of latitude/longitude to
a grid. For a good description of most of the other supported projection systems and a discussion of the
tradeoffs in using various projections, we suggest visiting
http://www.progonos.com/furuti/MapProj/Normal/TOC/cartTOC.html.
The Datum pull-down is used to select the datum to use in association with the projection. The most
commonly used datums are WGS84, NAD27, and NAD83. If you find that the datum that you need is not
available, you can use the Add Datum button to add your datum. When that button is pressed, the Create New
Datum dialog (pictured below) is shown, allowing you to enter the parameters for either a 3-parameter
Molodensky datum transformation or a 7-parameter Bursa-Wolfe datum transformation, or even specify a
transformation defined by a text file with a list of control points.
If you choose the Custom Shift Based on Control Point File option, the text file that you select should have a
series of lines defining the mapping from a lat/lon coordinate in the new datum and the corresponding lat/lon
value in WGS84. This is a very easy way to define a datum if you don't know any transformation parameters,
but do know the WGS84 coordinates for at least 2 coordinates in the new datum. The format of each line
would be as follows:
deg_longitude_in_new_datum,deg_latitude_in_new_datum,deg_longitude_in_WGS84,deg_latitude_in_WGS
The Abbreviation field is what will be displayed for the datum name in the status bar. If your datum uses a
prime meridian other than Greenwich, enter the longitude of the meridian used (relative to Greenwich) in the
Prime Meridian entry box.
The datum information will be stored in the custom_datums.txt file in the Global Mapper Application Data
folder (see the Help->About dialog for the location of this folder), so to share your datums just copy that file
to that folder on another user's computer. If a needed ellipsoid is not built in to Global Mapper, use the Add
Ellipsoid button to add a new one or Edit Ellipsoid to edit an existing custom ellipsoid definition.
Map GPS Coordinates - GPS Map Coordinates - GPSCoordinates Map 129