It’s now possible to obtain decimeter (10cm/4in) horizontal and vertical accuracy using a mapping-grade receiver! This presentation will cover the techniques and equipment necessary to achieve this level of accuracy. Such accuracy can be obtained in the field or back in the office after data collection. Decimeter-level accuracy addresses the area in between the survey-grade and the traditional “submeter” where GIS accuracy is typically defined. It is now possible to map locations and navigate to underground facilities, critical infrastructure, and utility features when decimeter accuracy is appropriate. Learn about the progress of Wisconsin DOT’s network of reference stations which will bring high-accuracy possibilities as well as high-productivity GNSS to all of the state once completed. The status of the network construction will also be addressed.

1. High-Accuracy GPS for GIS: From 1ft to 4in.
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CHICAGO --- INDIANAPOLIS --- KANSAS CITY --- MILWAUKEE --- ST. LOUIS/ST. PETERS

2. GPS Resources
• GPS Information:
– Seiler Mapping Support
http://solutions.seilerinst.com/
– Seiler Mapping Support Blog
http://seilermapsupport.wordpress.com/
– Trimble Knowledge Network “TKN”
www.trimble.com/tkn
– National Geodetic Survey (NGS):
www.ngs.noaa.gov
– Wisconsin DOT WISCORS GNSS Reference Network
http://wiscors.dot.wi.gov

3. Why High-Accuracy?
• Utilities
– Collecting assets/features accurately:
• collecting existing features or
• ‘as-built’ surveys
– Relocating assets/features
• Local & city government
– Urban asset databases
– Road centerlines
• Construction
– Preliminary site surveys
– As-built surveys for collecting asset information
– Environmental impact reports

4. Why Mapping-Grade?
• If your applications only require 4in-12in, these
systems are built for that level of accuracy.
• Cost of the high-accuracy mapping systems are
typically about half to a third of the cost of a
survey-grade unit.
• Mapping/GIS products are designed to work
well with attribute-intensive GIS data collection
projects.
• They integrate seamlessly with ESRI software
such as ArcGIS or other software to maximize
focus on data and workflows.

5. Accuracy Levels
• 12 inches
– GeoXH’05
– GeoXH’08 or ProXH
• 8 inches
– GeoXH’05 /Pro XH with
Zephyr/Tornado Antenna
• 4 inches
– ProXRT / GeoXH’08 with
Zephyr/Tornado Antenna
(close to base station)
– GeoXH 6000 Handheld

6. GeoXH (6000) Handheld
• 4 inch Horizontal accuracy after post-
processing (depends on distance to
base station).
• 4 inch Horizontal Live in the field with
VRS/RTN
• 4 inch Vertical Accuracy, but first to
degrade
• Typically requires about 30 seconds at
each point for post processing
• 10 to 15 positions per feature for VRS
• 3-foot Horizontal accuracy in the field
with SBAS/WAAS
• Integrated unit can be carried in your
hand. No need for cables or a
pole/backpack.

7. ProXH
• 8 to 12 inch accuracy after post-
processing
• Typically requires about 30 seconds
at each point
• 3-foot accuracy in the field with
WAAS
• Use with a mobile data collector,
tablet, or laptop.
• Communication via Bluetooth or
serial cable.

8. ProXH with Zephyr/Tornado
• 6-12 inch accuracy
after post-processing
• Typically requires
about 30 seconds at
each point
• 3-foot accuracy in
the field with WAAS
• Use with a mobile
data collector, tablet,
or laptop

9. ProXRT
• More consistent Horizontal and Vertical
accuracy because it is on a pole an
external antenna.
• 4 to 12 inch Horizontal accuracy after
post-processing (depends on distance to
base station).
• 4 to 12 inch Horizontal Live in the field
with VRS/RTN
• 4 inch vertical accuracy, but first to
degrade
• Typically requires about 30 seconds plus
at each point for post processing
• 10 to 15 positions per feature for VRS
• 3-foot Horizontal accuracy in the field
with SBAS/WAAS
• Omni-Star/GLONASS capable

10. Non-Integrated Options

11. Real-time vs. Post-processed
• Post-processed differential correction is when field-collected
data is corrected in the office.
• It requires a base station that logs data to publicly accessible
storage.
• Precision results are pretty standard with respect to distance.
• Real-time correction is a correction source that streams
correction data to the user in real-time.
• Conventional sources of this data are WAAS (SBAS), Omnistar,
Beacon, and regional reference networks.
• Precision results are highly variable.

12. Post-Processing
• Pathfinder Office or GPS Analyst for
ArcGIS
• Results:
10 cm + 1 ppm with modern
equipment

13. Post processed Differential
• Corrections applied in Pathfinder Office
software or GPS Analyst software

14. H-Star Processing
• Corrections applied in GPS Pathfinder Office software or
GPS Analyst
• Multiple CORS used
• Carrier phase float solution generated
• One base station within 50 miles or three within 120 miles.

15. Why use VRS for GIS?
• Do not need post-processing software
• Increased accuracy
– Better than SBAS/WAAS and or Beacon (these are
at best 1 meter horizontal)
– Doesn’t degrade with distance from the base as
with post processing
– You know live in the field your Horizontal and
Vertical accuracy
• Integrity monitoring
– QA/QC increasingly important for contractors

16. Real-Time for GIS
• 2 options for Real-Time Decimeter (4in) data
collection:
– Using real-time H-Star technology Geo XH or
ProXRT (VRS)
– OmniSTAR HP (ProXRT only)
• Real-time data collection
– Allows for in field verification...knowing that a
feature has been captured to the desired
accuracy level streamlines workflow and
reduces the risk of recollecting data
– For relocating assets accurately and efficiently

17. WISCORS
Network funded by
the NGS & DOT as
part of the WI
Height
Modernization
Project
Currently in WISCORS
To be added in 2012
Not yet constructed
Other agency owned

18. Additional VRS/RTN’s
Public Networks
• Minnesota DOT
• Michigan DOT
• Iowa DOT
• Indiana DOT
• Many other states
Private Networks
• Trimble VRS Now, Karanet – Illinois

19. VRS Data Flow
Reference
station data
streams back
to server
through LAN,
Internet, or
radio links

20. VRS Data Flow
Roving receiver
sends an NMEA
string back to
server using VRS
cellular modem.
Virtual Reference
Station position
is established. NMEA—GGA

21. VRS Data Flow
Server uses
VRS position to
create corrected
observables and VRS
broadcasts them
to the rover

22. VRS Real-time Settings

23. Cellular VRS Connection
• Must have cellular service in your work area
– Verizon, AT&T, Sprint, T-Mobile
– Data Plan is needed (differs from a voice
plan)
• A simple cell phone with a data plan is best –
avoid Blackberries and I-Phones
• Make sure “tethering” is enabled
• Carry spare batteries or bring an external
battery
• A bluetooth cell phone is better
• MiFi – Verizon, AT&T or Sprint

24. Datums
NAD83 • Choosing the wrong datum
(CORS96) can greatly shift your data!
• NAD27 to NAD83 could mean
an inconsistent 50 feet or
more Horizontal.
• “NAD83” has different
versions
I’m in – NAD83 (86)
“NAD83”
– NAD83 (91)
– NAD83 (97)
– NAD83 (CORS 96)
– IGS09

25. Datum Shift
• Know your correction
source.
• WAAS and Beacon are
different!
• Confirm your base station
if post-processing.
• Find one base station that
works and stick with it for
post processing
• Do a test point on a
certified known
location/control point
before starting a project.

26. Anything else?
• Proper GPS Form
• Canopy Conditions
• Software Updates
• Mounting Options

27. Questions?
Travis LeMoine
http://solutions.seilerinst.com
http://seilermapsupport.wordpress.com/
WWW.SEILERINST.COM
CHICAGO --- INDIANAPOLIS --- KANSAS CITY --- MILWAUKEE --- ST. LOUIS/ST. PETERS