Week 4 - Jan. 30, 2015 – Start GPS Exercise 1.Update tree datasets 2.GPS ppt 3.Discuss: a.Assignment b.Group proposal – due today c.Juno data collection.

Week 4 - Jan. 30, 2015 – Start GPS Exercise1. Update tree datasets2. GPS ppt3. Discuss:

a. Assignmentb. Group proposal – due todayc. Juno data collection – start today

4. Week 5 – Group data collection throughout the weeka. Equipment check out

5. Week 6 – Small group meeting with Dr. G. throughout the week

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Global Positioning System Overview

Components of GPS

1) Space Segment – Satellites

2) Ground segment - control stations

3) User segment - Receivers and base

stations

1. “Triangulation" with satellites. 2. Receiver measures distance using travel time of radio signals. 3. To measure travel time, GPS needs very accurate timing.4. Also, need to know exactly where satellites are in space.  5. Correct for delays of signal as it travels through atmosphere.

Space Segment

24 satellites in 12hour orbits.

Provides the user with between five and eight SVs visible from any point on the earth.

Control Segment• System of tracking stations located around the world• Master Control facility - Schriever Air Force Base, CO

Primary Data Capture

• Surveying– Locations of objects determined by angle and distance

measurements from known locations– Uses expensive field equipment and crews– Most accurate method for large scale, small areas

• GPS– Collection of satellites used to fix locations on Earth’s surface– Many types of GPS units available for data collection

There are several types of GPS that have differing levels of accuracy for the given location:

• Recreational GPS - most common - found at most sporting

good stores - good for within 3-5 meters.

• Car navigational GPS - same technology as recreational but

with some software to help put the point roads.

• Mapping grade GPS - considerably more expensive -generally

locate within a meter.

• Survey grade GPS - very expensive - locate within

centimeters.

– Mapping and Survey grade GPS can utilize software to be even more

accurate. 10

Total Station

Traditional equipment replaced with electro-optical devices.

Accurate to 1 mm.

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User Segment• GPS receivers and the user

community

$100

$1,100

Factors effecting accuracy

• Type of roving receiver

• # of satellites – 4

• Multipath

• Occupation Period

• Satellite elevations

• Selective Availability

May 3, 2000 May 1, 2000

Football stadium:

With SA - field or in stands.

With out SA - yard marker

SA - 95% of points within radius of 45.0 m

Without SA - 95% of points within radius of

6.3 m

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Geocaching

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www.geocaching.com

1/30/2015 In class Group Proposal The job for your group today is to write a one page experimental design that outlines how you propose to collect gps data using different 3 different roving receivers and then map

and analyze your data and reach some results about which gps roving unit is the most accurate.

1. Compare Extrex, Juno and iphone GPS (two apps):– What apps will you investigate for iphone (pick two)

2. What are your methods for collecting data?– how much data do you need to collect?– What will you compare it to for accuracy?– Where will you collect it?– When will you collect it?

3. How will you analyze (compare) your data?– What type of comparisons will you make with your data from the different units?– What software do you think you will use?– What results do you hope to show with your data and analysis?

4. What type of visual product will you create to illustrate your findings? (graph, map,etc.)

Due at the end of class today20

www.esri.com/news/arcuser/0104/rec-gps.html

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blogs.esri.com/esri/gisedcom/2013/03/08/comparing-the-spatial-accuracy-of-field-data-collected-with-smartphones-and-

gps-receivers/

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