Magellan MobileMapper - GPS Software, Руководство пользователя

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Defining a User Map Datum
Whether you are in the office using MobileMapper Office, or
in the field working with your receiver, the system lets you cre-
ate the user map datum you need.
However you will not use the same methods in the receiver
and in MobileMaper Office to define the semi-major axis and
flattening for your user datum.
In MobileMapper Office, you will use the conventional way of
defining a user datum, i.e. by entering the semi-major axis (
a ),
the inverse flattening ( 1/f ) and the other 7 parameters.
The method used in the receiver is different as it is based on
the use of parameters
∆
a (Delta A)and
∆
f (Delta F) –known as
the Molodensky parameters– instead of a and 1/f . The other 7
seven parameters are exactly the same as those in MobileMap-
per Office.
∆
a and
∆
f are defined as follows:
∆
a (m) = a(WGS 84) - a(Local Datum)
∆
f = f(WGS 84) - f(Local Datum)
Note that the flattening ( f ), instead of the inverse flattening
( 1/f ), is used in the expression of
∆
f . So we have:
Because the resulting
∆
f is a very small quantity, it is multi-
plied by 10 000 to make it easier to handle. (The resulting
value is closer to 1.) It is
this value that you have to enter in
the
Delta F
field on the MobileMapper Pro handheld screen.
The latest release of
receiver software allows
you to define the full
set of 9 parameters
defining a map datum.
After pressing MENU
and selecting
Setup>Map
Datum>Primary/Sec-
ondary and “USER” in
the prompted list, you
now have access to two
different screens on
which these 9 parame-
ters are presented:
1st screen:
Delta A (meters)
Delta F (X 10,000)
Delta X (meters)
Delta Y (meters)
Delta Z (meters).
2nd screen (select
Next> at the bottom of
the 1st screen to
access this screen):
Rotation X (sec)
Rotation Y (sec)
Rotation Z (sec)
Scale factor (ppm).
∆
f
1
1
f
---
WGS 84
( )
---------------------------
1
1
f
---
Local
( )
-----------------------
– =