Best Practices for GPS Data Collection

Mapping & GIS Boot Camp 2010

GPS Data Collection

Best Practices

Mapping & GIS

Outline

• New accuracy levels

• Requirements for improved accuracies

• Data Collection Best Practices

New Postprocessing Accuracies (as of December 2009)

• SiRF processing significantly improved– 1 to 3 meter accuracy for Juno™ SB and Juno SC handhelds

(and XC)

– Trimble® Nomad® G series handheld and Trimble Yuma®

rugged tablet computer unchanged

• GeoXT™ handheld and GPS Pathfinder®

ProXT™ receiver– 50 cm (HRMS)

• H-Star™ processing– 10 cm faster, at longer ranges, in tougher environments

– GLONASS postprocessing now supported for GPS Pathfinder ProXRT receiver

Why Isn’t Nomad (or Yuma) 1–3 m?

1m 2m 3m 4m 5m 6m 7m 8m 9m 10m

HR

MS

True / False (or Depends)?

• The specified accuracies for a Juno SB/SC handheld are easy to achieve in the ―real world‖

• The specified accuracies for a GeoXT handheld or ProXT receiverare easy to achieve in the ―real world‖

• The specified accuracies for a GeoXH™ handheld or ProXRT receiver are easy to achieve in the ―real world‖

Requirements For Improved Accuracy

1. Supported GPS receiver

2. Supported software

3. Software settings

4. GPS data collection

best practices

What Receivers Are Supported?

Receivers that log Pseudoranges or

Carrier:– GeoXH, GeoXT, GeoXM™ handhelds (all versions)

– GPS Pathfinder ProXT and ProXH receivers

– GPS Pathfinder Pro XRS, and ProXRT receivers

– GPS Pathfinder XB and XC receivers

– Trimble Recon® GPS XB and XC edition handhelds

– Juno ST, Juno SB, and Juno SC handhelds

– Trimble Nomad G series handhelds

– The GeoExplorer® 3 handheld (with carrier enabled)

Receivers That Aren’t Supported

• Format obsolescence

– The GeoExplorer 3c handheld

– The GeoExplorer II handheld

– The GPS Pathfinder ProXL receiver

• Omitted due to ‘age’

– ProXR*, Pathfinder Power, and Pocket

receivers

*Note: The ProXR and possibly the Power receivers may make it back

in the next TerraSync™ software release

Supported Field Software

• TerraSync™ software version 4.10 or later

• Trimble GPScorrect™ extension for ESRI

ArcPad software version 3.10 or later

• Applications created using the

GPS Pathfinder Tools SDK version 2.40

or later

Supported Office Software

• GPS Pathfinder Office software version

4.20 or later

• Trimble GPS Analyst™ extension for ESRI

ArcGIS Desktop software version 2.20

or later

Software Settings

If you intend to postprocess:• Always use left-slider ‘Productivity’ field software settings

• Correct using the new ‘Smart automatic filtering’ setting

For real-time-only work (no postprocessing):Use the GPS settings slider as usual, e.g.:

– Mid-slider for more accurate positions in easy conditions

– Left-slider to improve yield in difficult conditions

• Use best practices for GPS data collection

Data Collection

Best Practices

Data Collection Best Practices

Collect good quality GPS measurements

between features (30–60s minimum)

For example:

• Collect good measurements in the open, while walking

towards the ‘tough’ feature

• Then collect the feature

• Then collect more good measurements while walking

away towards the open.

Why? Good data before/after the feature helps the

postprocessor to smooth out jumps at the feature

Data Collection Best Practices

Keep GPS antenna correctly oriented to sky

• If you aim at the ground, it will pick up reflected

signals (multipath), and degrade accuracy

• This includes between features!

• Consider turning off the device, rather than walking

along with it pointing down

Data Collection Best Practices

How long should a point feature be logged?

• 5s is OK in good conditions, if the accuracy (CEA or PPA) is well under what you need. – This assumes you have good data before/after the

feature!

• In difficult conditions, or if the accuracy is less than desirable, log for 15s or 30s, or even longer if necessary. Or you could try walking into the open and carefully back to the feature.

More Best Practices For High Accuracy

Receivers

• Preserve carrier lock– The longer you can hold the carrier lock the better

your positions will be

– Tip: Sudden movements can break carrier lock in

difficult conditions

• Use an external antenna in tough

environments• Easier to get above your body

• Stronger signal reception

• Larger groundplane / less multipath

Things To Note

Antenna Type is important• Select the correct Antenna in the field software

• Helps the postprocessor get high accuracy results

from data in difficult environments

• Only relevant for H-Star and Standard Carrier

processing

Legacy Field Software With PFO v4.20…

What is needed for optimal performance in the

latest Engine?

1. Wide open mask settings

2. Not in Feature positions set to log at 1s

3. Carrier Logging on

More satellites

Data in between features

All types of data

ProXRT—Customer File

• Real-time corrected

(OmniSTAR VBS)

• PFO v4.10 result –

Code selected over

carrier

• PFO v4.20 result –

L1/L2 Carrier Float!

1.3m

Positions around a circular building

Field Session Challenge

• Using Best Practices:

– Collect at least 3 open site Point Features

– Collect at least 2 Point features under canopy

– Collect open site Line Feature (Path)

– Collect some Line Features under canopy

• Using a predetermined site, so follow

instructions in the field