Guidelines for Field Use of Garmin GPS Units

GPS Checklist:

q Copy an updated version of the master "allpc" shapefile and other digital basemaps, including topo quads and aerial photos, from the GIS server (V: drive) before the field season starts.

q Know what coordinate system (e.g., UTM, zone 10) and datum (e.g., NAD83) your project uses. The PRBO default is UTM, WGS84 (same as NAD83). In the UTM coordinate system, your zone depends on where you are (see map).

q Download your GPS coordinates daily, using GPS Utility (www.gpsu.co.uk/) or Waypoint+ (www.tapr.org/~kh2z/Waypoint/) shareware. It is not uncommon for Garmin units to die in the field. You will need a PC Interface cable to download your data and a registration key for GPS Utility. If you are unable to download, record your coordinates by hand in the field.

q Always carry extra batteries, especially if you’re not planning to revisit the site, and turn off your GPS unit when not in use to avoid draining the internal lithium battery. Contact Garmin (www.garmin.com) for replacement or repair under warranty if your unit dies.

q Submit copies of your GPS coordinate files to the GIS lab at the end of the field season for archiving and general mapping purposes.

In the Field

GPS Unit Setup

Before taking waypoints in the field, the GPS navigation display should be set up to match the coordinate system, horizontal datum, and units used at a particular field project’s location. The most common coordinate system used on PRBO projects is UTM (Universal Transverse Mercator), with some projects also using decimal degree coordinates (latitude/longitude). Most projects use a NAD83 (North American Datum of 1983) or WGS84 (World Geodetic System of 1984) datum. NAD27 is also used by some projects that work with federal agencies such as the U.S. Forest Service.

Your GPS navigation display only controls what you see in the field. When you download coordinates, it is not your GPS unit settings that determine which coordinates you save, but the settings on your download program (i.e., GPS Utility or Waypoint +). However, it is best to standardize all coordinate system/datum settings in order to avoid confusion.

The following general directions are based on the Garmin II, III, 12, and 76 series, but should be similar for other Garmin units. Please refer to your user manuals for specific instructions.

How to set up your Garmin GPS unit’s navigation display:

1. Navigate to the MAIN menu using either the PAGE or QUIT buttons.

2. Scroll down to the SETUP menu using the multi-directional pad and press ENTER.

3. From the SETUP menu, go to the NAVIGATION or LOCATION menu.

4. The POSITION FORMAT or LOCATION FORMAT menu item is where you will choose the type of coordinates that your GPS will display and record. Cursor down, highlight the currently selected value and press ENTER to scroll through the list of formats and highlight the one that applies to your project/location. For UTM, select UTM/UPS; for decimal degrees, select hddd.ddddd; for degrees-minutes-seconds (DMS) – select hdddmm.mmm.

5. Under the MAP DATUM or DATUM menu item, highlight the one that applies to your project/location, and press ENTER. Most commonly used are NAD83 and NAD27 CONUS.

6. CDI Scale settings (not found on all units): The course deviation indicator (CDI) lets you select the +/- range (sensitivity) of the CDI bar scale, letting you know how much your current course is deviating from your destination waypoint. It is probably best to keep this at its lowest setting (+/-0.25) to prevent you from straying too far from your destination.

7. Under the UNITS menu, select METRIC.

8. The HEADING or North Reference category applies whether or not you will be navigating using true north or magnetic north (automatic or user-defined). All units on a project should maintain the same settings as this will affect what direction you will need to travel to get from site to site. This especially applies if you are using your GPS unit to record compass bearings in your directions for the next person who needs to find the points! Record on your point count directions whether your bearings are true north, magnetic north, and/or what user-deviation (declination) was set when recorded. This will make finding poorly flagged points much easier for future observers when satellite coverage is poor. (See note on true vs. magnetic north.)

How to log waypoints:

1. Navigate to the satellite reception display using either the PAGE or QUIT buttons and wait until a 3D GPS location is reported (2D means your accuracy will be low, but it’s usually better than nothing).

2. If you have a WAAS-enabled unit (GPS 76 series, some Geko and Rino units), go to the general setup menu and make sure WAAS is enabled.

3. Hit the ENTER or MARK button to record your position. Use the multi-direction pad to enter an ID code for your waypoint. For point counts, enter the full site/station code if possible; it will make your life easier later. If you need more than six digits for your point count site/station code or nest code (and you are using an older Garmin that restricts the number of digits to 6), then take careful notes so that you can rename the waypoint record later. If your unit has an AVERAGE function, make sure to select this option and wait a minute or so before selecting SAVE.

4. Waypoints can be deleted or edited using the WAYPOINT LIST or POINTS menu.

How to navigate to a waypoint:

GPS units differ in their navigation functions, but in general, look for the NAV or GOTO button. Select the waypoint of interest and choose which window you want to use (compass needle or map) using the PAGE button.

Coordinate Systems, Map Projections, and Datums

UTM coordinates are “projected” coordinates, which means they reference a map projection (Transverse Mercator). A map projection is a method for converting the earth’s three-dimensional round surface to the two-dimensional planar surface of a map. Other commonly used map projections at PRBO include Albers equal-area and Lambert conformal conic (“equal-area” and “conformal” describe the properties of these projections). Latitude and longitude coordinates (degrees-minutes-seconds or decimal degrees) are referred to as geographic coordinates, meaning that they refer to an exact location on the earth’s three-dimensional surface. For more information on map projections see this USGS webpage: http://mac.usgs.gov/mac/isb/pubs/MapProjections/projections.html

Whether you are using projected (e.g., UTM) or geographic (e.g., lat/long) coordinates, you will need to reference a horizontal datum, which can be described as a base reference for a coordinate system. It includes the position of a point of origin, a network of surveyed control points, and a model for the shape of the earth. For more information on horizontal datums, see this ESRI website: http://www.esri.com/news/arcuser/0401/datum.html

True vs. Magnetic North

It's said that a compass points north. That isn't exactly true. The magnet in a compass aligns itself with the magnetic field of the planet. This field flows between the earth's two magnetic poles, the northern of which is the magnetic north pole. True north is the axial pole centered at the top of the planet where the meridians of longitude converge. Magnetic declination--the amount and direction of difference between true and magnetic north—changes with location. At Palomarin, for example, magnetic north is to the east of true north and the difference is approximately 15°. The variation is therefore 15°E. The variation in Chicago is 0°. From there true north is in line with magnetic north. The map below shows 2004 magnetic declination contours for the continental U.S. To calculate the declination at a specific study site, go to the following NOAA website: http://www.ngdc.noaa.gov/cgi-bin/seg/gmag/declination1.pl.

In the Office

Downloading GPS Waypoints

An important part of collecting GPS data is retrieving it quickly and efficiently, so that it may be used for analysis purposes later. Daily data downloads are STRONGLY encouraged in order to prevent loss of data. Every field office should have at least one data / PC interface cable (make sure that your cables match your GPS units). Once you are set up, this should take less than 5 minutes per day, and will save you frustration later if your GPS unit falls off a cliff containing the only copy of your data. Upload and download instructions can be found at http://www.prbo.org/tools/gps/gps.htm.

Generally, there are two steps involved in downloading GPS data:

Transferring coordinate data from your GPS unit to your computer (in text or shapefile format). This is best done with a shareware program such as Waypoint Plus (see http://www.prbo.org/tools/gps/WaypointPlus.pdf for instructions) or GPS Utility (see http://www.prbo.org/tools/gps/GPSU.pdf for instructions).
Importing coordinates into ArcView software for viewing with basemaps. PRBO’s Waypoint Express extension can be used to create shapefiles from Waypoint Plus text files (see http://www.prbo.org/tools/gps/WaypointPlus.pdf for instructions). If you use GPS Utility and export using the shapefile option, you can add the shapefile to your ArcView project directly (see http://www.prbo.org/tools/gps/GPSU.pdf for instructions).

Waypoint Plus (GPS download shareware currently used by many PRBO projects) is only compatible with older Garmin (PCX5 format) units. For newer Garmin units (including all WAAS-enabled units) you will need a different shareware program (GPS Utility is recommended). Please refer to the following table to determine which combinations will work together. Links to shareware and extensions can be found on the PRBO tools website: http://www.prbo.org/tools/gps/gps.htm.

Garmin GPS Model

Up/download Software

ArcView Extension

12/12XL

12CX

12Map

PCX5

format

II Plus

III Plus

126/128

180/185

215/225

Waypoint Plus

(www.tapr.org/~kh2z/Waypoint/)

GPS Utility

(www.gpsu.co.uk/)

Waypoint Express

(www.prbo.org/tools/gps/gps.htm)

None needed if shapefile option is used

GPS 72/76

GPSMap 60/76 series

eTrex series

Geko series

Rino series

GPS Utility

(www.gpsu.co.uk/)

None needed if shapefile option is used

Important: Contact the GIS lab for a GPS Utility registration key.

Uploading Coordinates to your Garmin GPS Unit

Uploading coordinates to your GPS is often necessary for re-finding point count locations, nests or other GPS’ed features that will help you navigate in the field. Some projects may wish to keep all waypoints on the GPS unit to circumvent this step, but space is limited (generally 500-1000 waypoints), and oftentimes coordinates will need to be transferred from one GPS unit to another.

From Waypoint Plus text files:

If you are using an older Garmin unit and Waypoint Plus shareware, the easiest way to upload coordinates is to save your Waypoint Plus download text files and use them to upload points back to your GPS unit. You can also combine several text files in one (as long as they are in the same coordinate system and reference the same datum) by cutting and pasting lines of text (each line is a waypoint) from one text file to another. Refer to the Waypoint Plus / Waypoint Express instructions for specific directions.

From Shapefiles:

If you have coordinates in shapefile format, you can do either of the following:

1. If you have an older Garmin unit (PCX5 format), use the Waypoint Express extension to export your shapefile to Waypoint Plus text file format; then upload the coordinates to the GPS unit using Waypoint Plus. (Refer to the Waypoint Plus / Waypoint Express instructions for specific directions.)

2. With any Garmin unit, you can use GPS Utility to upload shapefiles directly to your GPS unit, bypassing ArcView. (Refer to the GPS Utility instructions for specific directions.)

GPS Data Management / GIS Lab Coordination

At the beginning of each field season, project leaders should obtain a current copy of the “allpc” shapefile maintained by the GIS lab in the appropriate coordinate system and datum. This shapefile can be used to obtain coordinates for upload into GPS units, or for creating maps. Relevant basemaps such as roads, streams and topo quads can also be obtained from the GIS lab or copied from the GIS server at Palomarin or the Wetlands Center (v:/gis_data and v:/gis_projects directories).

At the end of each field season, project leaders should compile all point count, nest, and other relevant GPS datasets into one shapefile or Waypoint Plus text file (per data type) and submit them to the GIS lab via e-mail. Please make sure that the coordinate system, UTM zone if applicable, datum, and units are specified within the shapefile or in an associated text file.