iG5 User Manual
72
#11 Be Procedure Smart: avoid Blunders
Assuming that your receiver is in a location that is suitable for
GPS observations, at a suitable time, there are several
procedural blunders that you can do to force a bad result:
•
Mounting system is not level and receiver is not
centered over the ground mark.
•
Antenna height (HI) is wrong.
•
Antenna is mis-rotated, doubling antenna
compensation errors.
•
Wrong antenna type is selected.
•
No battery in head with external power
Use a Fixed Height Tripod, Get the HI Correct!
The #1 OPUS procedure failure is a blundered
instrument height. The ONLY HI that OPUS will
accept is the vertical height above ground to the
ARP (Antenna Reference Point) in meters.
If you use a tribrach, you are going to have to
make a slant measurement and then reduce the
slant distance and SHMP (Slant Height
Measurement Point) vertical offset to a metric
vertical height. The process is described on page
92 in the
section of this User Manual.
Slant reduction error is also very common source of
blundered instrument height. The iGx_Download tool makes
this computation automatically for you, however you must
keep track of Slant vs. Vertical and Feet vs. Meters.
Transposition of digits in random heights that occur with
tribrachs on tripods is a common source of error.
Measurement to the wrong place on the antenna is a
common source of error. Mixing slant measurements in feet
with metric SHMT and radius constants is a common source
of error. Confusing slant heights between multiple
occupations is a common source of errors.
Using ‘inch’ tapes
instead of ‘tenths’ tapes is a common source of errors.
