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SGU1
Information on the City of St George Community GPS Base
Hello All,
Todd Jacobsen and I have finished all of our planned enhancements to the city’s base station for this year. Here is a brief description of the changes:
Updated the receiver from a Thales ZMax (circa 2003) to an Ashtech ProFlex 500 (brand new). This was done with a grant from Ashtech that allowed us to purchase the upgraded equipment with an unspeakable factory discount.
Provided for (hopefully) days of battery backup
Changed the radio protocol from EOTT (End Of Transmission Timeout) to Trimtalk II, thus allowing all Trimble users access to corrections via UHF. (This necessitated reprogramming all other existing radios in the region.)
Added a second repeater near I-15 at the Washington City water tank.
Moved internet access from a dedicated Qwest DSL router to the City’s vastly superior (faster/reliable/managed) network.
Added DIP RTCM2 output for GIS receiver use.
Provided for hourly static RINEX files. You can now download RINEX for any moment during the previous 60+ days. We have added flash storage sufficient to store 2+ years of data. In a couple of years, when flash storage is even less costly, we will migrate the existing data to an even larger storage device.
Obtained a IERS DOMES registration for the antenna location (IERS DOMES 49432M001).
Are in the process of NGS National CORS system consideration for inclusion of this site. This will greatly enhance OPUS and OPUS-RS solutions for the region.
I thought that this would be a good time to publish access information and positional information for your use.
SGU1 General Information:
You should always be able to download the latest site log with this link:
ftp://209.33.248.96/sgu1.log.txt (user name ‘user’ password ‘sgu1’)
3.3 Receiver Type : ASHTECH PF500
Satellite System : GPS+GLONASS
Serial Number : 201129001
Firmware Version : s608Gt23
Elevation Cutoff Setting : 0
Date Installed : 2011-08-29T15:40Z
4.1 Antenna Type : ASH701945E_M
Serial Number : CR520030204
Antenna Reference Point : BPA
Marker->ARP Up Ecc. (m) : 0
Marker->ARP North Ecc(m) : 0
Marker->ARP East Ecc(m) : 0
Alignment from True N : 0
Antenna Radome Type : SNOW
Radome Serial Number :
Antenna Cable Type : BELDON RG-8 Braided
Antenna Cable Length : 30M
Date Installed : 2004-01-28
Access by UHF Radio
CMR+, Trimtalk II, 9600 baud, Scrambling/FEC ON
Main Frequency: 454.500 MHz
Utah Hill (West of Ivins): 454.400 MHz
Washington City (East of St George): 454.250 MHz
Real-Time Data via Internet
Streaming data is available from SGU1 via Direct IP:
IP: 209.33.248.96
PORTS: 7201 – CMR+
7202 – CMR+
7203 – RTCM3
7204 – RTCM3
7205 – RTCM2
7206 – ATOM
7207 – DBEN
Base Status and Configuration
You can view the base status using this address:
Server: http://209.33.248.96
User: user
Password: sgu1
There is a nifty web based mission planning tool available here: http://asp.ashtech.com/wmp/ if you need one.
Static Data via Internet FTP
You can download static data, in hourly RINEX files, using this link:
Server: ftp://209.33.248.96
User: ftpuser
Password: sgu1
Data is available starting from 6/27/2011 through the top of the last hour. The folders and files are arraigned with this format:
Obs: YYYY/ddd/sgu1/sgu1dddh.11o.Z
Nav: YYYY/ddd/sgu1/sgu1dddh.11n.Z
Where YYYY is the four character year (2011), ddd is the Julian day (244), squ1 (the site name), h is the UTC hour starting at ‘a’.
So a direct link to the midnight to 1:00 am UTC observation file for September 1, 2011 would be:
ftp://209.33.248.96/2011/244/sgu1/sgu1244a.11o.Z
If you click on the server link ftp://209.33.248.96, you should be able navigate through the directly structure in a web browser. Remember that we are currently UTC – 6 Hours, after the time change we will be UTC – 7 hours.
Base Position
There has been some discussion of the position of the base. The antenna was originally set January 28, 2004 and has never been moved. The base coordinates have been held from the initial installation and (to the best of my knowledge) have never been modified.
I just ran 10 24-hour days, spread over 30 days with three day spacing (29 July through 25 August), through OPUS, with these three CORS sites fixed: NVLM, NVPI, FRED. I have posted all of the observation data and OPUS reports at this web address for the untrusting:
OBS Files: http://www.alltopo.com/out/sgu1/OBSFiles.zip
OPUS Reports: http://www.alltopo.com/out/sgu1/10Day.zip
Here is a summary of the results:
|
|
|
|
NAD83 CORS96 |
||
|
FILENAME |
START DATE TIME |
HOURS |
UTM Northing (M) |
UTM Easting (M) |
EL HGT |
|
2011 |
All solutions use NVPI,FRED,NVLM |
|
|
||
|
210_2100.11o |
7/29/2011 0:00 |
24 |
4110520.966 |
271624.643 |
895.572 |
|
213_2130.11o |
8/1/2011 0:00 |
24 |
4110520.967 |
271624.639 |
895.577 |
|
216_2160.11o |
8/4/2011 0:00 |
24 |
4110520.968 |
271624.640 |
895.571 |
|
219_2190.11o |
8/7/2011 0:00 |
24 |
4110520.967 |
271624.641 |
895.575 |
|
222_2220.11o |
8/10/2011 0:00 |
24 |
4110520.966 |
271624.639 |
895.575 |
|
225_2250.11o |
8/13/2011 0:00 |
24 |
4110520.967 |
271624.644 |
895.574 |
|
228_2280.11o |
8/16/2011 0:00 |
24 |
4110520.966 |
271624.638 |
895.569 |
|
231_2310.11o |
8/19/2011 0:00 |
24 |
4110520.965 |
271624.640 |
895.583 |
|
234_2340.11o |
8/22/2011 0:00 |
24 |
4110520.967 |
271624.639 |
895.576 |
|
237_2370.11o |
8/25/2011 0:00 |
24 |
4110520.968 |
271624.642 |
895.573 |
|
|
|
|
|
|
|
|
|
|
AVG |
4110520.967 |
271624.641 |
895.575 |
|
|
|
Range |
0.003 |
0.006 |
0.014 |
|
|
|
StdDev |
0.000 |
0.005 |
0.004 |
The reference position (the position programmed into the base) is:
|
Current Reference Position |
|
|
|
|
|
|
|
From Installation thru 7/9/2011 0:00 |
|
4110520.965 |
271624.649 |
895.589 |
Thus there is a slight difference in the base position with respect to OPUS:
|
Delta from Current Reference Position (meters) |
|
0.002 |
-0.008 |
-0.015 |
Sean Fernandez also recently computed a comparable site position, I assume using TURN reference stations:
|
Sean Fernandez's Position |
|
4110520.974 |
271624.647 |
895.61 |
|
Delta from Current Reference Position (meters) |
|
0.009 |
-0.002 |
0.016 |
I also have some limited historic static data sets collected from 2008 through 2010 and the position of the antenna, as reported by OPUS, has not changed appreciably (contact me directly if you would like copies of this data). I believe the ‘Delta from Current Reference Position’ has been consistent since the station was set in 2004. By CORS standards, the difference is reasonable and very small.
If the site is accepted by NGS for inclusion into the National CORS system, NGS will provide us with a site position which we will adopt. At that time, we will provide everyone with plenty of warning. I suspect the horizontal change would be millimeters, and the height change would be less than 2 centimeters.
If the site is not acceptable to NGS, then at some future time, we as a community may want to change the reference position to exactly match some very long term OPUS average. I would suggest that we wait until after the next adjustment which is going to be implemented this month by NGS.
In any case, the existing site position:
37°06'47.48102"N 113°34'13.02300"W 895.589 m NAD83, CORS96
is the same as we started with, is extremely good and is defendable.
Which GEOID Should You Use?
Obviously, the base position is set to an ellipsoid elevation (not orthometric). Thus you will need to add the geoid separation to directly read an orhtometric height. (Some have suggested that we use an orhtometric height for the base position: J )
There are three possible choices GEOID99, GEOID03 and GEOID09. When this base was originally commissioned, the correct answer was GEOID99.
The latest geoid implementation is the 2009 model. The difference between these three models is substantial. For the ARP of SGU1, these are the three GEOID values:
|
GEOID Comparisons |
|
Geoid Dif |
Orhto |
|
|
|
GEOID99 |
-24.399 |
919.974 |
|
|
|
GEOID03 |
-24.472 |
920.047 |
|
|
|
GEOID09 |
-24.493 |
920.068 |
|
You can see there is nearly a 9 cm difference in apparent orhtometric height over the three models.
I can’t tell you which one you should use. I will suggest that GEOID09 will best match HARN and OPUS. The City of St George continues to use Geoid99 as to not disrupt their elevation database.
The Future
If this base is accepted for inclusion into NGS CORS, we will drop you a note. If it is, we will see significant improvement in South Western Utah OPUS-STATIC solutions and huge improvements in OPUS-RS solutions.
Currently our plans for next year (2012 July Fiscal) include:
Please drop Todd ( todd.jacobsen@sgcity.org ) or I ( ms@igage.com ) a note with other suggestions.
Todd incurred a substantial and unbudgeted hit when he obtained a FCC license for the new Washington repeater. He is accepting donations small and large to help offset the expense. Consider chipping in a few bucks, the base has been a great community resource for almost a decade.
Good survey and mapping to you all,
Mark Silver, ms@igage.com
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