May your bearings be true

1
GPS Exercise
May your bearings be true and your
course over ground rewarding!
2
In the area shown in the reference map (next
slide), complete the following exercise 1.Collec
t 10 waypoints per group as indicated by group
(130-300) Group 1 Restaurants Group 2
Street Car Stops Group 3 Buildings and
Sculptures in Audubon Park (fountains, etc.) 2.
Add waypoints to a map using GIS software
(330-430pm)
3
Reference Map Uptown New Orleans
N
Source MAPQUEST at WWW.MAPQUEST.COM
4
GPS Basics Concepts

• To understand how a GPS function, it is necessary
  to understand three key concepts
• DATUM
• COORDINATES
• TRUE NORTH vs MAGNETIC NORTH
• BEARING
• COURSE OVER GROUND(COG
• WAYPOINTS
• SELECTIVE AVAILABILITY(SA)

5
DATUM
DATUM refers to a particular kind of map system.
The two most common Datum's that you will
encounter in the US may be NAD 27 ( North
American Datum of 1927 ) and WGS 84 (World
Geodetic System 1984 ). Other countries may use
different datum. WSG 84 is standard.
6
COORDINATES
A system incorporated into maps / navigation
systems to locate points on earth. Coordinates
may be angular as in Latitude / Longitude or
rectangular as in UTM ( Universal Transverse
Mercator). The UTM format is based on a system
of grid squares that cover most of the world and
at the greatest resolution forms squares 1000
meters by 1000 meters. If you look at one of
these squares you can estimate a location within
a couple hundred meters even without making a
measurement - quite an advantage over the
Latitude / Longitude procedure. This system is
based on a series of 60 grids starting at the
International Date Line running East around the
world.
7
BEARING
Refers to the direction to a waypointthe compass
direction from your position to a destination
TRUE NORTH vs MAGNETIC NORTH
TN The direction indicated by a line of
longitude MN The direction that the north needle
on a compass needle points (in the absence of
local magnetic interference)
8
WAYPOINT
A specific location saved as precise geographic
coordinates (i.e. lat/long) in the receivers
memory
COURSE OVER GROUND (COG)
The direction a GPS receiver is actually
traveling (it does not matter which ay it is
facing)
9
May your bearings be true
and your course over ground rewarding!
10
SELECTIVE AVAILABILITY (SA)
With SA activated you could expect accuracy
within 300 feet 95 of the time. However, on May
12, 2000 SA was discontinued. As such it is now
thought that the civilian GPS user can obtain
position readings with errors usually no worse
than 60 feet with a possible "normal accuracy
within 33 feet. SA could at some future date be
activated in the event of a national emergency.
11
SELECTIVE AVAILABILITY (SA)

Before (ON) and After (OFF)
May 1, 2000 SA ON
May 2, 2000 SAOFF
Latitude
Latitude
Longitude
Longitude
12
WHERE IS YOUR SCHOOL?
Datum NAD 27
http//www.geocode.com/eagle.html-ssi
13
Location of Tulane University