Graybeard Outdoors banner
1 - 8 of 8 Posts

·
Registered
Joined
·
2,281 Posts
Discussion Starter · #1 ·
My Garmin Etrx Venture HC shows the same location with Google Earth (set on same units) but my Garmin Topo US 2008 is not accurate using the same units. I've emailed Garmin about it. Doesn't the USGS use UTM units now?

I have my GPS set up with:
position format/ utm ups
map datum/ nad27 conus
display/ degrees
north preference/ magnetic

BTW, I really like this little Venture GPS. It comes up quick and is easy to use if you're already familiar with a Garmin GPS. I'm thinking about getting Delorme TOPO USA. I like it. I don't know if you can use it with a Garmin GPS though.
 

·
Registered
Joined
·
3,532 Posts
USGS maps use both UTM and LAT/LONG normally displayed in degrees, minutes, and seconds. Old USGS maps use LAT/LONG.

Out in the woods you will find public agencies and private timber company “K” tags with Township, Range, and Section display, and a nail in the tag at the location the tag is found.

Here are some contacts with people currently doing mapping for USGS in West Virginia..


West Virginia
Statemap
West Virginia Geological and Economic Survey --Michael Hohn, 304-594-2331, [email protected]
Quadrangle(s):
Bethany
Burlington
Mannington
Valley Grove
Edmap
West Virginia University --J. Steven Kite, 304-293-5603 x4330, [email protected]
Quadrangle(s):
Davis
Lead Mine
Saint George

Here is some reading regarding map standards. Item #6 is key, but does not provide a clear answer. From my reading USGS and other Federal Agencies
http://ngmdb.usgs.gov/Info/standards/dataexch/STATEMAPguidelines.html

A lot of the USGS maps have not been updated for years. Most topo map software for gps units is scanned and coded by the gps manufacture from USGS maps.

A couple of weeks back I stopped and bought the updated Shasta-Trinity National Forest map at the Mt. Shasta Ranger Station. It is based on Township, Range, and Section along with LAT/LONG.
In the past I have had good success transferring data from my Garmin gps to Google Earth. It is a good fit.

A couple of years ago I pulled some landmarks from the CAD(Computer Aided Dispatch) I used the LAT/LONG and UTM provided in the system to first locate the landmark on my National Geographic State Series Topo software. There was no problem. I next tried it Google Earth and the locations in Google Earth were about 300 feet off. A check was made to make sure the setting for the coordinates was the same, and they were confirmed.

The next step was to have a Chief Office confirm the LAT/LONG on the ground.

The conclusion was that Google did not line-up in our few test cases. Now Garmin is still on the hook because there are errors to be found in the maps. USGS has an allowable error in production maps. Google Earth has up dated their software and some of the views since the experiment were conducted.

http://www.natgeomaps.com/software.html

Seating here at my computer I just download some waypoints, tracks, and routes to the desktop from the gps. Viewing them in Map Source they appear to be okay, and then I used the Map Source Option to View in Google Earth. Everything seemed to line up.
 

·
Administrator
Joined
·
26,228 Posts
Out in the woods you will find public agencies and private timber company “K” tags with Township, Range, and Section display, and a nail in the tag at the location the tag is found.
I used to run up on those all the time in the National Forests here. I don't think I've seen one tho in 20-25 years or more now. I wonder what happened to them. Perhaps they are no longer used around here.
 

·
Registered
Joined
·
3,532 Posts
They disappear because of vandalism, and some mental giants think they were put out there for target practice. It cost a lot of money to survey property lines, and the product of that labor is lost when the K tags or other monuments disappear.

When I was training S&R deputies I told them if they were not sure where they were in the woods and they found a “K” tag they could use the information it to find themselves on a Forest Service or BLM map.

Here is a “K” tag put up by a private land company.
 

·
Registered
Joined
·
2,281 Posts
Discussion Starter · #5 ·
Thanks for the info. I hunt some timber co. property (Westvaco) during deer season. The trees are marked with paint at property corners and along the property boundry.

Any tips for the settings on my GPS? I have NAD27 CONUS selected and went back to degrees, minutes, and seconds instead of UTM.
 

·
Registered
Joined
·
3,532 Posts
If your gps is loaded with Topo 2008 or earlier Garmin Map Source product I recommend that you use WGS 84. Any other Map Datum may create errors within the United States.

The conflict comes in when you have a map based on WGS 84 in your gps, and you have a map in hand based on an older Datum such as NAD 27 or NAD 29. When you have that situation you will generate errors because they are based on different systems, and the ability to measure the Earth has vastly improved over the years. Garmin says that by matching the Datum in your gps with your paper map the Unit will:
Datum—select from over 100 available map datums, allowing MapSource to easily match up with virtually any paper chart or map, or manually enter information for a user defined map datum.

The difference in NAD 27 may be wide or narrow. At the dispatch pod we have built in maps based on WGS84 data. It is not uncommon for a unit to call in wanting the land status at a certain LAT/LONG. Accuracy is dependent on all parties using the same Datum, I am aware of errors up to a few hundred feet. The joker is the error rate is not consistent because of variables in the survey. When it was found that a farmer had been moving a Meridian monument around when he was plowing his field land lines in a large area needed to be resurveyed.
http://www.blm.gov/cadastral/meridians/Caleneva.htm
http://www.blm.gov/cadastral/meridians/pob.htm

This links helps spell out the history of the survey system in the U.S.

http://en.wikipedia.org/wiki/Public_Lands_Survey_System
 

·
Registered
Joined
·
2,281 Posts
Discussion Starter · #7 ·
Thanks. I haven't loaded any topo software in my GPS yet. I'll play around with it and see what happens.
 

·
Registered
Joined
·
2,281 Posts
Discussion Starter · #8 ·
I figured out my problem. ME! The topo map is lacking in definition. Where I "thought" my house is on the topo map, it ain't!

If you have topo US by Garmin and wonder if the position is correct, there is a selection under "view" that allows you to select "view in google earth". If you put your way point on the topo map and then select "view in google earth" and the way point is where it should be on the satellite image you're good to go.
 
1 - 8 of 8 Posts
Top