Best Field Practices Collecting GNSS Field Data

Mark Payne - Frontier Precision907-858-1500 Office907-203-2204 Cell

markp@frontierprecision.com

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

Mark Payne

Frontier Precision

907-858-1500 Office

907-203-2204 Cell

markp@frontierprecision.com