MoDOT Post-Processing - Seiler Instrument

Seiler Support Note June 2010
Post Processing MoDOT Base Station Data
Seiler Instrument has developed the following procedure to allow our Mapping customers to
access the Missouri Continuously Operating Reference Stations GNSS RTK Network data via
the internet for post processing. The existing MoDOT RTK Network was developed and is
being maintained and expanded by the Missouri Department of Transportation (MoDOT RTK)
Geodetic Survey Unit. It is a Global Navigation Satellite System (GNSS) reference station
network which includes Global Positioning System (GPS) signals. The network consists of
permanent CORS sites which provide real-time correctors to mobile users and provides stored
files for post processing.
Users must manually download base files using the MoDOT RTK RINEX Shop interface on
the MoDOT RTK website to post process data in Trimble Pathfinder Office (PFO) or Trimble
GPS Analyst extension for ArcGIS. MoDOT RTK does not allow automatic access to data
through the Trimble software wizards. MoDOT RTK Rinex files are kept on the server for 60
days.
User must have a MoDOT RTK logon user name and password to access the MoDOT RTK
data. Obtaining a logon may take a day or so to obtain. Apply for Logon at:
http://gpsweb.modot.mo.gov/ then click on sentence New users may register here to obtain
full service of this website or just use guest account below. You cannot access the CORS
data via a Guest logon.

Quick Steps
• Manually identify the timeframe for your data to be post processed
• Create a folder to save base files to (User need only do this once on a PC)
• Download data from MoDOT RTK website
• Make MoDOT RTK Data ready for post processing- duplicate the navigation files
• Start the Differential Correction Wizard
• Process data within 20 days as MoDOT doesn’t store the data more than 20 days
Manually identify the timeframe for your data to be post processed
1. Open file or files to be post processed in PFO
2. Verify Time zone setting is correct
• Select Options Time Zone
Central Std (-6) November 2, 2009 - March 8, 2010
Central Day (-5) March 8, 2010 - November 1, 2010
3. Document the time span for the data to be post processed. Write down Date and Time to
manually get the matching files from MoDOT RTK RINEX Shop web server. Be sure to
cover entire data timeframe.
• View Timeline. Select option View Timeline (check will appear in front of
Timeline if it is active)
Or
• Open the Data Position properties window
• Select the First feature and Last Feature.
4. Exit Pathfinder Office
Create a folder for all base files (User need only do this once on a computer)
5. If this is the first download from MODOT RTK, use Windows Explorer to create a folder
to store all future MODOT RTK base file downloads
• Create a folder C:\pfdata\MoDOT RTK\base
NOTE: If you do not create this folder in this exact location, the post processing wizard will not
know where to look for the base files- location must be C:\pfdata\MoDOT RTK\base
After post processing, all files in this folder may be deleted. During the actual post processing
correction process, the wizard copies the needed base data to the current project/ base folder
in a subfolder named for the CORS site.
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Download data from MODOT RTK website
NOTE: MODOT RTK Rinex files are kept on the server for 60 days.
6. Open Internet Explorer and navigate to MODOT RTK RINEX shop and download data
• Go to http://gpsweb.modot.mo.gov/
7. You must have a user logon to access the RINEX SHOP
• If you have a Login and Password, fill it in
• If you do not, then click on the link for new users and
obtain one
NOTE: Logon and password are always “lowercase”
letters
• After entering Login and Password, press Submit to
continue
8. Start a RINEX Download
• Click on MoDOT RINEX Shop link in navigation bar at
left
• Click button Start New Order
• Click on Continuously Operating Reference
Station (CORS) hyperlink to proceed
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8. Start New Order and Select “CORS”
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NOTE: If you are working inside the MODOT RTK network area, you should never be
more than 50 miles from a single base station. For H-star processing, if project area is
within 50 miles of a single MODOT RTK station, user should Use a single base
provider. If distance to base is greater than 50 miles, user should select Use multiple
base providers. If you are not certain of the distance, download all stations in the
working area and a distance from your work area and the CORS will appear when
selecting the CORS during the post processing to help you decide what provider to use.
• Click the green plus on the map
to highlight the MODOT RTK
station(s) that you want to include
the base data you require
• CORS name/s should highlight in
blue on the list to the right
• If you click the same station 2x it
will UN-Select itself
OR
• Press and hold Ctrl Key and pick
all required station directly in the
list on the right
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9. When finished selecting CORS, press NEXT: TIME SELECTION > > at the bottom of the screen
REMINDER: Process data within 20 days as MoDOT doesn’t store the data more than 20 days.
Note: CORS selected should all be listed at the top of the page
10. Select correct DATE for your project. One day plus unlimited hours per download. If you have multiple days
that are not in consecutive order, you must do multiple downloads to avoid huge size files.
11. Select GPS Time:
[GPS time during Daylight Savings Time (March - November) = Local time + 5 hours]
[GPS time during Central Standard Time (November - March) = Local time + 6 hours]
Example
3PM on March 3 is 1500 hours plus 6 = 21h
3PM on March 18 is 1500 hours plus 5 = 20h
12. Set Duration to be sure your job file collection time is covered
13. Set Interval select 1s
14. Check the box select Include Broadcast ephemeris as this is required to post process data- if you miss
this check box- you will have to repeat entire download!
15. Press NEXT: ADD TO ORDER > >
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16. Review Order, ensure at least one file includes Eph. (yes)
• add stations if needed
• then press NEXT: DELIVERY OPTIONS > >
17. Select a notification or delivery method. Then Toggle the radio button to the RINEX option and press
NEXT: GENERATE DATA > >
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NOTE: User does not need to wait for file to download. This is the reason you cannot access the RINEX Shop
as a Guest, your downloads are stored under your logon.
• User can log off and the file will be waiting upon next logon-
• User can start another download immediately
• User can wait then download
18. Click on < < BACK OVERVIEW to see files progress OR Click on Next Order Details >>
19. Once the file appears available to Download, click on Download and save to the folder you created in Step
5: C:\pfdata\MoDOT RTK\base” folder. OR follow the instructions you received via e-mail if you chose that
option. “Send by e-mail” is not recommended for 4 or more plus hours of data depending on your internet
speed, e-mail and firewall restrictions.
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Make MODOT RTK Data ready for post processing- duplicate the navigation files
20. Unzip the recently downloaded data to the same folder c:\pfdata\MoDOT RTK\base. You may delete the
zip file now or delete after processing is complete.
• Only one Navigation file is created when RINEX Shop delivers a download zip file. You need to Copy
and Paste the “n” file (Navigation file) as many times as you have CORS selected.
• Each CORS station must have a “N” file with a matching name pre-fix
Example: MOSP022P.10n is for the MODOT RTK Station MOSP in St Peters
If you downloaded from other base stations during this same download session then Copy
MOSP022P.10n and rename the copied file to that of another base station MORW22P.10n for
MORW in Warrenton etc.
Start the Differential Correction Wizard
1. Re-open PFO or GPS Analyst and open file\files to be post processed
2. Select menu option Utilities Differential Correction…
• Select SSF files to correct dialogue box will appear. SSF file/s that were open when the wizard was run
will appear in the list else press the
Differential Correction Wizard.
button and navigate to and add any other SSF files to the
• Click on Next >
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3. Set Processing Type Select Automatic Carrier and Code Processing
• If H-star option is enabled, and work area is within MODOT RTK network, select radio button Use single
base provider
NOTE: If you are working inside the MODOT RTK network area, you should never be more than 50 miles from
a single base station. For H-star processing, if project area is within 50 miles of a single MODOT RTK station,
user should Use a single base provider. If distance to base is greater than 50 miles, user should select Use
multiple base providers and surround your work area with 3 CORS (triangulate as best as possible).
• Press Next >
• Verify Correct Settings. If re-correct real-time positions does not appear, press Change… button to
configure settings.
• This page will look different depending on what version of Pathfinder Office you are using. PFO 4.10 is on
the left and PFO 4.20 is on the right:
o Check the box to re-correct real-time positions and press OK then Next >
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On the Base Data Screen: Click the Browse radio button and select Browse: to locate the base file you
recently downloaded.
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Reference Position: select radio button Use reference position from base files and click Select…
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Check “on” Confirm base data and position before processing and click Next > this will allow you to see if
you have 100% coverage and if you have any datum shift from the base file
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Select the type of output settings and then click Start
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Press Confirm to perform differential correction and watch the process
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****CAUTION: CORS reference frames: mixing and matching datums will cause your post processed data to
come out poorly. All stations entered into the Trimble Base Provider list should have an entered reference
position based on ITRF00 (Epoch 1997) in the Base provider properties dialogue box. The published MODOT
RTK positions on the internet at http://gpsweb.modot.mo.gov/ are referenced to the current NGS adjustment
(NAD83 (NSRS2007)(Epoch 2002). Check against known control points on your GIS before committing to a
large post-processing project.
Contact Seiler Instrument at 314-218-6321 for details or questions regarding this Support Note
SUP-7.5.1, WI1 Rev. 1, 3/29/07
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