best field practices collecting gnss field data mark payne...
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Best Field Practices Collecting GNSS Field Data
Mark Payne - Frontier Precision907-858-1500 Office907-203-2204 Cell
THE GNSS SYSTEM
• Original GPS System 21 Operational and 3 Spares
• Today the GNSS Constellation consists of over 50 Satellites
WHAT DID YOU SAY?
GPS works in
Geographic or Lat/Lon,
HAE in Meters
UTM –Universal
Transverse Mercator,
XYZ
U.S. State Plane
Projection, XYZ
Custom Projection
XYZ
Localized Projection
XYZ
GPS’s Native language is latitude
longitude (lat/long), Height
Above the Ellipsoid (HAE) in Meters
(3.28083333333ft), but can be
Transformed to any Map Projection
7 THINGS YOU MUST KNOW
• Datum
• North American Datum 1983 (NAD83, 2011)
• Projection
• Geographic
• Projection, State Plane, UTM
• Projection Zone
• Alaska 4 5004
• UTM Zone 6
• Altitude Reference
• HAE (Height above the Ellipsoid)
• MSL (Mean Sea Level)
• Geoid Model
• Geoid 2012B
• Coordinate Units
• U.S. Survey Feet or Feet
• Meters
• Altitude Units
• U.S. Survey Feet or Feet
• Meters
COORDINATED SYSTEM (WHEN DOES IT MATTER)
• Office
• Selecting Coordinates off of the screen Pathfinder Office (Desk Top)
• Uploading of Waypoints to Waypoint Manager (Import)
• Selecting Coordinates from Desktop Software (PFO)
• Exporting Data to GIS
• Field
• Keying in Coordinates to Field Software for Navigation (Way Points)
• Selecting Coordinates from Field Software (map view) or other
locations within File Software
• Giving Coordinates to other field team members (selecting off screen
or in File manager
Recommendation: Field Software, Office Software (desktop) and Export
settings all be set to Coordinate System as per the Job requirements.
DGPS REMOVES ERROR
Xds?
Base on known point
Rover
X
Rover Receiver Must use the same SV or a sub set of SV’s as the base station
Time, t
T+1
?
All Measurements logged at the base and the rover contain error. In addition, all
measurement have a time stamp!
DXYZ
GETTING STARTED
?
Survey Control (The 5 W’s)
Who set the control? (Trusted Source)?
What were the procedures used in setting the control?
When was the control set? (Is it possible to recover the control)?
Why was the control set? (xyz), (xy), (z) coordinates?
Where was the control set? (Is the control in a suitable site for a GPS base station)?
Consider Setting your own Control
Use OPUS which is part of the CORS Network for setting Control Point using a Survey Grade Receiver.
CORS enhanced post-processed coordinates approach a few centimeters relative to the
National Spatial Reference System, both horizontally and vertically.
Note: SBAS using the newest WGS84 realizations is generally coincident with ITRF;
according to National Geospatial Intelligence Agency (NGA): the comparison of
WGS(G1762; 2005) to ITRF2008 (2005) "is zero by statistical analysis[; m]ean differences
are 1-2 millimeters and significantly less than the error in the conversion…
PPA AND CEA
PPA (Predicted Post Process Accuracy) is used to show you live in the
field what your post-processed accuracies will be.
CEA (Current Estimated Accuracy) is used to show your estimated
accuracy when collection a real-time correction source or autonomous.
HIGH ACCURACY USING VRS
DGPS USING CORS NETWORK
CORS NETWORK (SITE DETAIL)
DGPS OPTIONS
• Set up your own Base Station in local project area• User VRS via cellular communication• Use Single Base Station via radio cellular Communication• Use SBAS• Use CORS
Single Base Station
Radio or Cellular
SBAS
VRS
Cellular
CORS
User Base Station
x
HIGH ACCURACY DGPS
• Set up your own Base Station at local project
• Centimeter level post processing option• Decimeter level post processing option
• What are Base Lines
• Base Lines is the physical distance between a base station and a rover.• Base Lines distance effects Post Processing and Real Time DGPS results normally (1 ppm)
X Control PointBase Line
X Rover
Base lines < 20K will yield +/- 1 centimeter H, +/- 1.5 centimeter V
Base lines <100K will yield +/- 20-30 centimeter H, +/- 50-60 centimeter V
DGPS OPTIONS “REVIEW”• Data Collection
• Post Processing (CORS, User Base Station on site)
• Real Time using (Users Base Station on site, VRS or Single Base via Cell )
• Real Time using (SBAS)
• Real Time (SBAS / Post Processing)
• Mixed Data Sets, SBAS / Post Processing (careful here mixing DGPS)
• Source of Coordinates (accuracy)
• GIS = How was the data created?
• GPS
• Type of receiver used to collect data? (Accuracy of GPS unit)
• Post Processed
• Real time (remember your datum)
• Precision vs. Accuracy Known Point
Precision
Precision vs. Accuracy
Precision and Accuracy
HOW TO IMPROVE DATA QUALITY
• Use a current Almanac
• Acquire new Almanac (15 Mins)
• Ephemeris (7.5 Mins) (Allows GPS Fix)
• Acquire (3 Mins) of Carrier Data, starting
and ending base or rover file.
• Use a Range Pole with “External Antenna”
• Set and control Height antenna height
• Collect data over the point
• Plum up over the point
• Better Reception
• Better Quality Antenna, larger internal ground plane
• Stronger signal reception
• Get’s the antenna away from the body
• Allows you to extend the GNSS Antenna height using a extending range pole
AVERAGING POINTS AND VERTICES NODES
• More accurate point and node positions
• Averaging Point data, 10-20 positions
• Longer observation if quality of positions are bad, or abandon
Feature and start again
• Averaging Vertex on line of polygon
• Allows Averaging of a number of positions to form a single vertex in
line or area will result in best quality positions within vertex
Averaging Point Data XXX
X
HOW TO IMPROVE DATA QUALITY
• Avoid Multipath if possible
• Trees
• Buildings
• Hard surfaces
• Other things that Affect GPS
• Electrical interference
• Microwave
• Radar
• Clocks (Great but not Perfect)
• Atmospheric (Water Vapor)
HOW TO IMPROVE DATA QUALITY - PDOP
Dilution of Precision (DOP)
An indicator of satellite geometry for a unique constellation of satellites used to determine a
position. Positions tagged with a higher DOP value generally constitute poorer measurement
results than those tagged with lower DOP. There are a variety of DOP indicators, such as GDOP
(Geometric DOP), PDOP (Position DOP), HDOP (Horizontal DOP), VDOP (Vertical DOP), etc.
The Lower PDOP = better Positions
HOW TO IMPROVE DATA QUALITY
• Offsets using Laser Range Finder
• Ideal for difficult access locations
• Single point offsets
• Multipoint offsets
• Height and widths
• Line measurements
• Automatic offset calculation
N
Point Feature
GPS
Bering
HOW TO IMPROVE DATA QUALITY
• Laser Range Finder Workflow
• Position (One Shot)
• Height (Three Shots)
• Width (Two –Three Shots)
• Measure (Bering, Inclination, Range
and Missing line)
HOW TO IMPROVE DATA QUALITY
Use a Data Dictionary
• Saves time
• Consistence data input
• Allows admin control of data
input
• Allows conditional selection
based on previous entry
HOW TO IMPROVE DATA QUALITY
• Creation of Data Dictionary
• Start with a blank sheet of Paper
• Write down what features you wish to collect
• Write down the attributes you wish to collect for each feature
• Have reviewed by your colleagues
• Take proposed written Data Dictionary to field (near Office if Possible)
• Make necessary adjustments to design of Data Dictionary
• Program Data Dictionary into software
• Load Data Dictionary to data logger
HOW TO IMPROVE DATA QUALITY
• Data Dictionary Creation
HOW TO IMPROVE DATA QUALITY
Spatially distributed entities, activities
or events
• Points have a single geographic coordinate such
as:
–Transformer
–Tree
–Lamp post
HOW TO IMPROVE DATA QUALITY
Spatially distributed entities, activities or events
• Areas (Polygons) are a series of geographic coordinates joined together to form a boundary such as:
–Lake
–Land Parcel
HOW TO IMPROVE DATA QUALITY
Spatially distributed entities, activities or events
• Lines (Arcs) are a series of geographic coordinates
joined to form a linear feature
such as: Road, Trail, or Power Line
HOW TO IMPROVE DATA QUALITY
Attributes
The possible attributes of a road
• Surface type
• Width
• Condition
• Name
• Lanes
HOW TO IMPROVE DATA QUALITY
• Use Photos
• Geotagged
• Provides more information about feature
• Visual record of feature
• Seamless integration in ArcGIS
• Photos linked to features
HOW TO IMPROVE FILE MANAGEMENT
• Data Management
• Use a Tree Structure (example)
• Easy to find data going years back
• Keeps Team data separate
• Large Projects a must!
• Never misplace data
• For your Sanity!!!
KNOW YOUR RECEIVER ACCURACY (SPECIFICATIONS)
Trimble Geo 7 Series with H-Star and Floodlight
• Centimeter (1-2 cm) VRS or (Local Base Station)
• Sub foot (30cm) (Post Processed)
• Sub Meter (75 cm) (SBAS)
Trimble R1 with Tablet (Real Time / Post Process)
• Sub Foot (30 cm) (post processed) with Terrasync
• Sub Meter (75 cm) (SBAS)
• Sub Meter with Arcpad (Real Time Only)
• Sub Foot with Arcpad and (Trimble Positions, Post
Process)
NEW TRIMBLE R
• Works with the following;
• Trimble Tablets
• IPads
• Computer Tablets
• IPhones
• Droid Phones
• Trimble GPS Units
Sub Meter on all Platforms
Trimble R
NEW TRIMBLE R2
• Works with the following;
• Trimble Tablets
• IPads
• Computer Tablets
• IPhones
• Droid Phones
• Trimble GPS Units
Sub Meter on all Platforms
Trimble R2
JUNIPER SYSTEMS
• Works with the following;
• Trimble Tablets
• IPads
• Computer Tablets
• IPhones
• Droid Phones
Sub Meter on all Platforms
Juniper Geode