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One year's experience with a recreation-grade GPS receiver. Pete Bettinger Warnell School of Forestry and Natural Resources University of Georgia Athens, GA Songlin Fei Department of Forestry University of Kentucky Lexington, KY. 7th Southern Forestry and Natural Resources GIS Conference.

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One year's experience with a recreation-grade GPS receiver

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One years experience with a recreation grade gps receiver

One year's experience with a recreation-grade GPS receiver

Pete Bettinger

Warnell School of Forestry and Natural Resources

University of Georgia

Athens, GA

Songlin Fei

Department of Forestry

University of Kentucky

Lexington, KY

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Overview

There are three general classes of GPS receivers used in natural resource

management:

• Consumer- or recreation-grade

• Mapping-grade

• Survey grade

Recreation-grade receivers

generally provide the least

accurate positional

information - between 3 m and

10 m accuracy under optimal

conditions.

However, recreation-grade receivers have become popular among many

outdoors enthusiasts, and this popularity has likely influenced the wide variety of

inexpensive GPS receivers available on the market today.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Overview

Which type of receiver to choose?

It depends on your application, and your cost considerations.

If single-fix errors of 5-20 m are acceptable, then a recreation-grade receiver

would suffice.

Also, recreation-grade may be acceptable for locating field points when you know

you will be in one location for some time (allowing the capture of multiple fixes).

When mapping large areas, where the error concerning the perimeter is small

relative to the size of the area, then a recreation-grade receiver may also be

acceptable.

Ultimately, the cost of data collection and the desired accuracy of referenced

positions should be balanced.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Objectives

The objectives of this research were to compare the accuracy of horizontal position

locations in different timber types, and across different seasons and months of the

year.

In addition, the research was aimed at examining the influence of air temperature,

relative humidity, atmospheric pressure, and planned positional dilution of precision

on the accuracy of captured position locations.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Methods

Three GPS test points were selected from the 40 available at the Whitehall Forest

GPS Test Course in Athens, GA.

The test points are located in a young pine plantation (15 years old), an older,

natural pine stand (over 60 years old on average), and a mature hardwood stand

(over 60 years on average).

The three test points were visited once per day over the course of a year, and 50

position fixes (waypoints) were collected during each visit, with each position fix

captured within 2-3 seconds of the previous.

Young pine stand:

15 years old

130 ft2 per acre basal area

450 trees per acre

Hardwood stand:

60-70 years old

88 ft2 per acre basal area

144 trees per acre

Older pine stand:

60-70 years old

86 ft2 per acre basal area

59 trees per acre

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Methods

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Methods

A Garmin Oregon 300 was selected for use in this study.

WAAS was disabled for this study to ensure that the data

were collected under consistent circumstances.

Planned PDOP was collected from Trimble GPS planning

software.

Data were downloaded to a computer using Minnesota

DNR Garmin software.

Some warm-up time was necessary to ensure that a sufficient

number of satellites were available to provide a reasonable

position fix.

Visits were randomly selected, and each test point was visited within about 2-3

minutes of the previous point.

During each visit, the GPS receiver was plumbed over each control point, and the

operator stood on the north side of each as data was collected.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Methods

Accuracy of the horizontal positions collected was evaluated by using the root

mean square error (RMSE).

RMSE is the raw difference between collected measurements and the control points,

and places greater weight on larger errors since the error term is squared.

A correlation analysis was performed between the RMSE values and the following:

Forest type

Planned PDOP

Air temperature

Relative humidity

Atmospheric pressure

Solar wind speed

Weather data were derived from the Weather Channel and Weather Underground.

Solar wind speed data were acquired from the Advanced Composition Explorer (ACE)

Science Center at Cal Tech.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

Samples were taken on 289 days between September 15, 2008 and September 14,

2009.

Range of data accuracy (RMSE)

Young pine stand

Older pine stand

Hardwood stand

Best

(m)

0.5

0.2

0.8

Worst

(m)

38.2

46.2

28.7

Mean

(m)

11.9

6.6

7.9

Median

(m)

11.5

5.8

7.3

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

Scatter-plot

of position

fixes by

stand type.

• Accuracy is

influenced by

forest type.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

5-day moving average RMSE

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

RMSE by relative humidity - no correlation

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

RMSE by atmospheric pressure - no correlation

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

RMSE by air temperature - no correlation

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

RMSE by solar wind speed - no correlation

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

RMSE by planned PDOP - no correlation

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

Significant differences

• Several significant differences between stand types.

Fall / Winter

1. Error in hardwood stand vs. error in the younger pine stand.

2. Error in older pine stand vs. error in the younger pine stand.

Spring / Summer

1. Error in hardwood stand vs. error in the older pine stand.

2. Error in hardwood stand vs. error in the younger pine stand.

3. Error in older pine stand vs. error in the younger pine stand.

Entire year

1. Error in hardwood stand vs. error in the older pine stand.

2. Error in hardwood stand vs. error in the younger pine stand.

3. Error in older pine stand vs. error in the younger pine stand.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Results

Significant differences

• No significant difference, for data collected within a single stand type, between

seasons of the year.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Discussion

Results are preliminary, and more analysis is forthcoming.

7th Southern Forestry and Natural Resources GIS Conference


One years experience with a recreation grade gps receiver

Questions and Comments Welcome

One year's experience with a recreation-grade GPS receiver

Garmin Oregon 300 tested on the UGA GPS Test Course

7th Southern Forestry and Natural Resources GIS Conference


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