User's Manual

English
49
Coordinate
Systems
When creating a new DXF job or when creating a layer as the
first layer in a new *.map job, MobileMapper Field asks you
to define a coordinate system.
Choosing a Coordinate System
Proceed in this order:
1. Choose the World Geodetic System or the country where
your field operations will take place
2. In the field just underneath, choose the datum used
3. In the field just underneath, choose the projection used.
4. Choose the vertical datum in the last field. The default
possible choices are:
– Ellipsoid: Each altitude or height value is simply
determined with respect to the selected ellipsoid
(second field above).
– EGM84: Each altitude or height value is still initially
determined with respect to the selected ellipsoid but a
correction is applied to that value. The correction is
read from the EGM84 geoid (Earth Geoid Model 1984,
a global geoid model) and is specific to the computed
horizontal position.
Other geoid models may be downloaded to the receiver
from the MobileMapper Software CD. Once downloaded,
they are made available as possible choices in the Vertical
Datum field.
The Properties... button at the bottom of the screen allows you
to view the properties of the selected datum and projection.
The New... button at the bottom of the screen allows you to
create a user system (datum + projection).
Defining a User System
• Tap on the New button.
• Select the type of projection you wish to use in your
coordinate system. Depending on that choice, you will
have to enter a certain number of parameters.
Remember every time you create a new projection and you
have to enter the latitude and longitude of origin, or the
central meridian, these must be expressed in degrees with
eight decimal places (ddd.dddddddd). On the other hand,
false eastings and false northings should always be
expressed in meters, even if a different unit has been
selected in the Units field on the same screen.
• After you have named and defined your new projection
and datum, just tap OK to save the new system and choose