45 CHC i83 User Manual
GPS 'Settings' Tab
The GPS Settings options on the download tool are only compatible with these receivers:
X90, X91+, X900+, X900S, iG3, iG4
For other receivers use the Wi-Fi connection to make recording interval changes. Check the hardware manual that came
with your receiver.
The ‘Log’ Tab
The ‘Log’ tab shows detailed results of the current program operation. It may be useful to debug some aspects of file
processing.
OPUS: What is it?
OPUS (Online Positioning User Service) is a free service provided by the NGS (National Geodetic Survey.)
From the NGS Website:
“This Online Positioning User Service (OPUS) provides simplified access to high-accuracy National Spatial Reference System
(NSRS) coordinates. Upload a GPS data file collected with a survey-grade receiver and obtain an NSRS position via email.
OPUS requires minimal user input and uses software which computes coordinates for NGS' Continuously Operating Reference
Station (CORS) network. The resulting positions are accurate and consistent with other National Spatial Reference System users.”
Here are links to more detailed information:
http://geodesy.noaa.gov/INFO/OnePagers/OPUSOnePager.pdf
http://geodesy.noaa.gov/OPUS/about.jsp
One of the most important contributions to vertical accuracy computed by OPUS is the length of occupation. Longer
times are better. If you are concerned about elevation, please remember that a 2-hour OPUS static observation has an
expected height accuracy of 2.5 cm. A 6-hour occupation has an expected accuracy of 1.5 cm.
OPUS-RS (Rapid Static)
Standard OPUS-Static sessions require 2 hour observations. OPUS-RS sessions can be as short as 15 minutes.
OPUS-RS solutions are not available universally. In general, OPUS-RS needs:
3 (or more) CORS within 250 km of your site
your site must be within 50 km of the polygon formed by the CORS sites
If you are working in Southwest Nevada, along the high line of Montana or in North or South Dakota, OPUS-RS probably
will not succeed, and you will need to collect at least 2-hours of data for submission to OPUS-STATIC.
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