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iGage
iG8 User Manual
Advanced Base Configuration
The Quick Start Guide
When you are configuring a base in SurvCE, you are faced with 6 choices for initializing the Base position:
In general:
‘Read From GPS’: If you don’t know the position of the base, click on ‘Read From GPS’ to use an ‘Autonomous
Base Position’. With WAAS corrections the autonomous position will be within 2-meters of the true ITRF2014
position. If absolute coordinates are needed, you can translate the job to OPUS or a control based position. See
the section ‘
Adjusting Data Stored with an Autonomous Base to an OPUS Position
‘Enter Lat/Lon’: If you know the geographic coordinates (Latitude / Longitude) from a control sheet use ‘Enter
Lat/Lon’, you can enter either the orthometric or ellipsoid height.
‘Enter Grid System Coordinates’: If you know the State Plane Coordinates and you are working in State Plane
at Grid use ‘Enter Grid System Coordinates’.
‘Previously Surveyed Point’: If you have been working on a job and have surveyed your base position as part of
a previous setup, then you should be able to use ‘Previously Surveyed Point’.
‘Use Local Coordinates’: If you want to have Local Coordinates (like 10,000, 10,000, 0) for the Base with a
geodetic or state plane basis of bearings, at Grid or at Ground then select ‘Use Local Coordinates’. WARNING:
be careful with ‘Use Local Coordinates’ it is completely different than ‘Enter Grid System Coordinates’.
‘Read From File’: If you have previously setup on the job, and you stored a .REF file, use ‘Read From File’
But the correct method is: ‘It depends...’
The Real Word Guide
Setting a base is covered in the Carlson SurvCE User
Manual on Page 147 in section ‘
5.4 GPS Base
.’
The Bottom Line
When you configure the Base, the goal is to tell the GNSS
base receiver what the actual coordinates for the
electrical phase center (PC) of the GNSS antenna is,
including the actual ellipsoid elevation.
If you specify a projected Grid Coordinate, then SurvCE
will convert it to the equivalent Latitude / Longitude /
Ellipsoid Height.
In SurvCE you always provide the Ground Mark (GM)
elevation. SurvCE will convert to Ellipsoid, add the
vertical rod height HI (which may need to be derived
from a slant measurement) and the L1 offset (determined
by the antenna model) which describes the offset from
the receiver’s ARP at the bottom (Antenna Reference
Point) to the electrical phase center (PC) of the internal
antenna.
In other words: you supply the X, Y, Orthometric Height
of the point on the ground and SurvCE computes the
Latitude, Longitude and Ellipsoid Height of the antenna
phase center. This antenna position is transmitted to the
GNSS engine with a command to ‘Be a Base’ and
corrections are generated for transmission to the Rover
based on this known position.
Programmed Position Must Match True
Position
It would make things simple if you could enter any
position and elevation into the GNSS receiver and it
would just work. In fact, this is exactly how the ‘Use Local
Coordinates’ button works.