Professional Data Collection Techniques

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Professional Data Collection Techniques
John B. Muellerjohn_mueller_at_geoline.com818.760.4
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Geoline California
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How to be a Professional Data Collector

• How to get the best accuracy possible
• How to be the most efficient in the field
• Make life easier in the field
• Better quality results

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What is the right tool for the job?

• Survey Grade
• Centimeter accuracy
• 2 GPS system (base and rover)
• 40k investment
• Mapping Grade
• Submeter/50cm accuracy
• All-in-one total system
• Exports to all GIS/CAD formats
• 4000 - 11,000 investment
• Recreational Grade (Garmin, Magellian)
• Many claim to use WAAS for high accuracy
• Typically not able to export data for GIS uses
• 100 - 500

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GPS is Expensive!

• Are you getting the most bang for your buck from
  your GPS purchase?
• Make sure your department/company is utilizing
  the GPS to its full functionality
• The cost will be quickly offset with the
  efficiency and quantity of data taken in the field

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Survey vs. GPS Mapping

• If youre using sub-meter mapping-grade GPS,
  dont tell someone that youre doing a survey
• Surveying civil engineering/land surveying
• The word survey is becoming a legal description
  and includes a high level of accuracy when
  collecting data

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How accurate is Mapping grade GPS?
Depends on correction method
Autonomous

• 10 meters

Real-time Code Accuracy
Post-Processed Code Accuracy
Carrier phase Accuracy
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First Sigma of Precision

• Mapping Grade GPS is specified at sub-meter
• Legal description follows
• Sub-meter first standard deviation (68) of the
  time
• Of 100 points collected, 68 of them will be
  within specified accuracy

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Horizontal vs. Vertical Precision

• ROT Vertical percision is 2-3 times less
  accurate than the Horizontal
• Thus, I do not recommend GPS Mapping equipment
  for those doing drainage, or anything insisting
  on high vertical precision

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3 Areas to Perfect

• Pre-field Planning
• Better Data Collection Techniques
• Back to the Office (lets be gone by 5pm)

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Before You Even Go Outside

• Know your environment
• Have enough batteries
• Quickplan
• Data dictionary/Table creation creation
• Become more productive in the field by better
  pre-planning in the office.

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Knowing Your Environment

• Hills/Topography
• Buildings
• Trees
• Multi-path area (cars, lakes, etc)
• Areas to recharge GPS batteries
• Inaccessable areas
• Barbed wire
• Creeks
• Property boundries
• Might need a Laser for doing offsets

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Data Dictionaries

• Define the data to be collected in the field
  before you leave the office
• Ensure consistency with GIS data
• NO need to know Visual Basic to create
• And, easily add new items to the data dictionary
  in the field
• An unexpected new feature
• A new menu item in an attribute value

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Our Object in the Field?

• Become a Smart User
• These are things I believe to be true. My
  opinion. Actual results may vary.

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Know Your Equipment

• Make sure you are properly trained on the full
  functionality of the system.
• Do not cover the antenna when collecting data
• Remember to have fully charged batteries
• Remember to turn off power when not in use
• Most users only utilize 25 of functionality of
  GPS

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GPS has a GPS Compass

• Compass in GPS for navigation is not a magnetic
  compass.
• Start moving to allow the GPS to acclimatize and
  give direction

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PDOP

• Precision Delusion of Position
• Number based on satellite geometry
• Just because you have 10 satellites, doesnt mean
  you have a great position

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QuickPlan

• Before going into field, run Quickplan software
  to determine best time for GPS satellite coverage
• Different times of the day are better/worse for
  coverage

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In-field mission planning

• Planning skyplot
• View future satellite constellation, including
  trajectories and trails
• Use time in the field more efficiently
• Increase productivity

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Pause/Continue Line Option

• How do I keep my line and area features in a
  strait line?
• When collecting line data in a strait line, use
  the Pause/Continue function to ensure that the
  line stays strait.
• Helps keep data clean-up in the office to a
  minimum

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Distance vs. Time data collection

• Line and area features can be taken based on
  distance or time
• Distance option is better when traveling in
  vehicle or in long distances or big areas
• Time option (default) is better when doing more
  curved lines and areas

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Benchmark it!

• Attempt to find a survey/GPS benchmark in the
  area of data collection
• If no professional benchmark can be found, use
  permanent, obvious objects that can be seen from
  aerial photography and easily navigated to

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Make Me More Productive!

• How to get the best possible accuracy
• Differential Correction Review
• Real-time Differential Correction
• New Software Functionality
• Averaged vertices
• Range Pole Options
• COGO- offsets
• Email-internet connections
• Imagery in background

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How to get the best possible accuracy

• Stable Antenna
• Use range pole with bubble level for best results
• Longer occupation time does not always mean
  better results
• Occupation time should be at least 31 seconds
• Look for multipath

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Common Questions

• How long should I occupy a point in the field?
• 31 seconds (minimum)
• Base stations and Real-Time services typically
  only record a point every 30 seconds.
• There are 27 satellites up there, so no need to
  wait for enough coverage

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Errors in GPS Positions

• Obstruction
• Multipath
• Atmospheric Delay

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Obstruction
Multipath
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Multipath
Ionospheric Effects (B)
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Atmospheric Delay

• GPS signals are delayed
• as they pass through
• the atmosphere

Ionosphere
Troposphere
Rover
Base

10 km
Review Questions
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Differential Correction

• Corrections applied in Pathfinder Office software

Real time DGPS
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Real-time Correction Sources

• Coast Guard Beacon
• Free, limited coverage, relatively accurate,
• ground based signal
• Satellite Differential
• 800 per yr, most accurate, satellite signal
• Wide Area Augmentation System
• FAA, free
• full US coverage
• least reliable
• least accurate
• satellite based signal

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Coast Guard Beacon- How it works

• Base stations in Chico, Pt Blunt, Pigeon Point
• Base station collects
• at the same time
• in the same vicinity
• tracking the same satellites
• Transmit ground based corrections via radio
• RTCM 104 Standard
• Received by integrated Pro XR receiver
• Beacon-on-a-Belt with Geo Explorer
• Accuracy

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Coast Guard Beacon- Coverage

• www.navcen.uscg.gov

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Satellite Differential- How it works
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WAAS- What is it?

• Wide Area Augmentation System
• Created by the FAA
• Free-to-air differential correction to augment
  GPS
• Broadcast from geostationary satellites
• Can be used as infill source to backdrop another
  source

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WAAS- How it works

• http//gps.faa.gov/programs/waas/howitworks.htm
• 25 ground reference stations in US
• Received GPS signals
• Data sent to Master Control Site
• Corrections are transmitted to geostationary SVs
• SVs broadcast to WAAS-capable receivers
• Receivers decode WAAS signal for correction
• Not as accurate as Coast Guard Beacon
• No Initial Oprational Capability (IOC) (2003??)

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WAAS- How it works
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WAAS- Why I dont like it

• Lays 12-15 degrees above the horizon to the South
  West
• Hard to use if any obstructions, hills, etc.
• Several other GPS companies promote their
  equipment is sub-meter solely based upon using
  this technology

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Using Integrated DGPS
Setup in the data collection software

• Menu option
• Beacon
• Satellite
• WAAS
• Use uncorrected GPS or Wait for real-time
• For satellite differential
• Select provider
• Select satellite

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DGPS Do I need it?

• If data collection is the primary goal, DGPS is
  not absolutely necessary
• All data should be post processed anyway, thus
  reducing the need for a real-time GPS connection
• Primary use of a Real-Time DGPS is for navigation
• make sure that a base station is within the
  specified distance

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Making life easier in the field

• File Attributes
• Configuration Files
• Data Dictionaries
• Continued lines areas
• Averaged Vertices
• COGO
• Send/receive Email

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Mobile GIS
Mobile GIS involves GIS-enabling an
organizations field workforce where they work.
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ArcPad or TerraSync?

• ArcPad Mobile GIS
• Requires GPS Correct.
• TerraSync- Full-featured data collection and
  maintenance.
• Works seamlessly with Trimble products.
• Uses Super Correct
• Time saving tools

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Comparison to ArcPad
ArcPad 6.0
TerraSync 2.30
Yes
Customized User Interface
No
No
Yes
Close up navigation screen
No
Data Dictionary Support
Yes
No
Repeat Features
Yes
Laser Rangefinder Interface
No
Yes
Segment Line Features
No
Yes
No
WAAS Support
Yes
No
Yes
Status Flags (New, Imp, Upd)
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TerraSync Software
A Versatile GIS Data Collection and Maintenance
Tool
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Introduction

• Runs on Ipaq, Pocket PC series, TSCe
• Quality position and attribute data
• Runs under Power PC and Windows CE operating
  environments
• Part of the GPS Pathfinder family

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Map Background Data

• Use raster background maps in the field
• MrSid, BMP and JPEG images
• Download and display data directly from an
  Internet Map Server
• ArcIMS
• Open GIS

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Digitizing

• Collect features when GPS signal reception is
  poor
• Click on the map to create a position or key in
  coordinates manually
• Ideal for use with background imagery and
  traversing
• Do NOT use this method forprimary data
  collection or if you are lazy.

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External Sensor Data

• Record digital data directly
• Reduce error
• Laser rangefinders
• Record distances, offsets and heights
• Depth sounders, tree calipers, flow meters, etc

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COGO- Offsets

• Ideal for difficult to access locations
• Defined by
• Distance, bearing and inclination
• Distance-Distance, Triple Distance
• Bearing-Bearing, Triple Bearing
• Line and area offsets
• Input manually or by using a laser rangefinder

5ft
Stop
5ft
5ft
TS Demo
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Attached Files

• Attach files as attributes of a feature
• Digital image - a picture of the feature
• Sound recording - a verbal description of the
  feature
• Sketched diagram - historical records
• Files attached in the field automatically stored
  and transferred with the data file

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Send/Receive via Email

• Send files directly to the field
• Data files (SSF or SHP)
• Data dictionaries
• Configuration files
• Email completed projects
• back to the office
• GeoXT is nowBluetooth!

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What do I need?

• Wireless Service
• Ricochet Wireless Webb Connect
• Cellular modem to ISP
• Internet email account
• Microsoft email program
• Supplied by the Win CE OS
• Set up a Device in PFO
• Use latest Data Transfer module

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TerraSync for GIS Data Update

• Open existing file in TerraSync
• Select a feature to update
• Navigate to the feature
• This is where real-time DGPSwould come in handy
• Update positions and/or attributes
• Mark the feature as updated
• Close the file

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Map Background Data

• Use raster background maps in the field
• MrSid, BMP and JPEG images
• Make sure there is geo-reference file
• Download and display data directly from an
  Internet Map Server
• ArcIMS
• Open GIS

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Status Display

• Range of comprehensive GPS status display
  screens
• GPS satellite information
• DGPS status
• Receiver status
• Allows advanced troubleshooting

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Back in the Office

• Cleaning up data
• Differential correction
• Exporting
• These are things I believe to be true. My
  opinion. Actual results may vary.

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Base Station Rules

• Base stations independantly owned/operated
• ALWAYS POST PROCESS
• Base stations typically do not charge for data
  (not true in all countries)
• Feel free to contact them
• Base stations typically dont keep base data
  archived more than 30 days.
• Try to use a base station within 100 miles.
• Less distance is better

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Check Results

• Pathfinder Office has ability to check the
  percision of data collected.
• Check results compared to real-time solution

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GPS Quality vs. Image Quality

• How come the GPS data wont match up with
  satellite imagery or aerial photos? My imagery
  is 1 foot resolution.
• Image resolution has nothing to do with how
  accurate they are in real world coordinates.
• Georectifying
• Ground-truthing

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Questions?
Thank you !