|
| |
|
You have downloaded and printed topo maps of your area. You have spent
countless hours this past winter reviewing those maps. You have found a
number of possible sites to investigate. You also have that new GPS that
you just had to have this past Christmas sitting on your desk. Can you use
the two together? And if so, how? Well read along and let's see. It is much
easier than you think, after all, if you can master that computerized metal
detector, you can do this. It will take a little patience and practice, which
makes perfect, right?
|
| |
|
I will be using a Garmin 12 GPS in my examples, but most GPS receivers will
be similar in setup. I do not claim to be a GPS expert in any way, shape or
form. Please do not email me questions concerning about doing the following
to your brand of GPS receiver.
|
| |
|
Step One: Setting up your GPS
|
|
Your GPS must be set to match the Topo Map Datum. I am not going to go into
detail explaining datum's, as there are a number of sites that do a much better
job than I could ever hope to. Just trust me to set your GPS to the same datum
as the topo map. Most topo maps use NAD 27 (North America Datum-27).
Click here to see why the Datums must match.
This can be found on the bottom left corner of the topo map and will
read: 1927 North American Datum (NAD 27). Another line to note here is the line
"1000 meter Universal Transverse Mercator zone 17". Remember the "zone 17" as
you will need this when you enter waypoints in the GPS.
The zone number will vary depending on the topo map.
|
|
Click here for more datum info: http://www.joe.mehaffey.com/maps.txt
|
| |
|
On the Garmin you can do this by entering the "Setup" then selecting "Navigation"
and then "Map Datums" and selecting "NAD27 CONUS".
|
| |
|
Next, you need to use the UTM grid, not the Latitude/Longitude grid. The
UTM grid gives a more accurate position on the topo maps and it much, much
easier to use than Latitude/Longitude. This is also done at
the "Navigation" menu. Select "Position Formats" and finally "UTM/UPS".
|
| |
|
While you are here, change the "Units of Measure" to "Metric", as the
UTM grid
on 1:24000 scale topos is 1000 meters or 1 Km squares. Don't you wish now that
you had learned the metric system in school?
|
| |
|
All of the above is just a general guide and may be different for your brand of
GPS receiver. Read your GPS manual for your receiver if you have any questions
about setting the above items.
|
| |
|
Step Two: Getting the UTM Coordinates from the Topo Map
|
| |
|
Now we need to read the UTM coordinates of our site from the map which
we will enter into the GPS. On the sample topo map image below, our site
is shown circled. You will find that reading UTM coordinates from a topo map
is easier and more accurate using a scale. This site offers free scale downloads
or you can buy them. http://www.maptools.com/FreeTools/UTMtools.html
These files are in PDF format. I printed them on a clear plastic sheet and
they work great.
|
| |
|
Look at the image below and notice the following:
Note the thin black vertical and horizontal lines. These are UTM grid lines.
On the 1:24000 scale topo maps they are 1000 meters or 1-kilometer squares.
Most topo maps DO NOT have these UTM grid lines, I have added them to the
digital maps I use using the DRGTools.
|
| |
|
Now note the numbers at the top of the map with the thick black horizontal
lines above and below them, the small 6's and larger 25 and 26. These are
the Easting coordinates. The numbers on the right side of the image with
the single black line below them, the 4496 and 4497 are the Northing coordinates.
These larger numbers are the principal digits. These numbers locate the tic
marks where the UTM grid goes.
Note how these numbers increase by 1000 as you go right and up, which is the
same way you plot or read coordinates: Right then Up.
|
| |
|
Follow the grid lines 4497 and 626 until they meet, this lower left corner
of the square in which our site is located is our starting point. Place your
UTM scale at the bottom left of these two grid lines. We can now determine
our sites UTM coordinates. Since we know the grid box we are in, we have
part of the coordinates already:
|
|
6260 E and 4497 N
|
|
We need to find the Easting coordinate first. Placing the scale on the map
and reading right from the 626 grid line, we find that our site is approximately
100 meters from the 626 grid line. Thus our sites Easting becomes: 626100 E.
Now read up on the scale to the sites location. We find that the sites is
about 520 meters from the 4497 grid line. So out Northing becomes: 4497520 N.
That's it, with a little practice this becomes easier and easier.
|
| |
|
|
| |
|
If you have digital topo maps you can also get the UTM coordinates of the site
using the USGS Dlgviewer. Just zoom in on the area of interest and place the
mouse cursor over the site on the map. Now, note the bottom right corner of
the screen: write down the numbers for the UTM coordinates. To find the zone
and the datum of the digital scanned map, select the "Tools" menu and then
"Control Center". Click the "Metadata" button and then the "GeoTIFF" tab.
Here you can find the zone and map datum.
|
| |
|
Step Three: Enter the UTM Coordinates of the site into the GPS
|
| |
|
Turn on your GPS and goto the "Main Menu". Select "Waypoint" and press
"enter".
Select "New" and press "enter". Give your waypoint a name such as "house1".
|
| |
|
You can also change the waypoint icon here if you wish. I find that the default
icon is fine. Select the next field which is the UTM coordinate field and
press "enter". Enter the ZONE of the topo map you are using. This is found at
the bottom left of the topo map, in our example it is 17 T.
Next enter the easting, which in our example was 626100. Enter 4497520 as
the northing coordinate. Press the enter button. Hilight "Done" and press
"enter" to save our new waypoint.
|
| |
|
That's it, when in the field press the "Goto" on your GPS and select the waypoint
for the site you want, and off you go. Good Luck.
As of May 2000, selective availability is turned off, and GPS receivers are
now more accurate.
|
| |
|
I hope this article has helped you clear up the using a GPS with your metal
detecting. All comments are welcome. Let me know if this article was useful
or not.
|
|
(c) 2001 Randy Steele
|
|
| |
| |
|
A great way to get to know your GPS better is to try Geocaching.
|
|
Find one in your area and try it. http://www.geocaching.com
|
| |
|
|
|
The above photo shows my girls finding their first cache! They Loved It!!
|
| |
