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GPS for Measuring Straight-Line Distances?

Discussion in 'Hunting' started by Drakejake, Jul 12, 2007.

  1. Drakejake

    Drakejake Well-Known Member

    This may be the wrong place for this question, but I bet someone here knows about this. I want to measure straight-line distances on a tract of wooded land. Can I do this with one of the GPS handheld devices made by Garmin, for example? I am talking about distances of up to a half mile in hilly terrain.


  2. igpoobah

    igpoobah Well-Known Member

    Yes, but accept the fact that you could be several feet off just by the nature of how GPS works...

    If you have a GPS that can do averages, you can get it closer...
  3. GRIZ22

    GRIZ22 Well-Known Member

    Keep in mind GPS measures distances from above on a flat plane (works fine on the ocean) but will not take into account hills. Not a problem if you were measuring for a range. The major factor is what igpoobah mentions.
  4. ArmedBear

    ArmedBear Well-Known Member

    Measure them?

    Not directly. The odometer feature tracks actual distance walked or driven, so that would include up and down hills.

    What you can do, though, is put in a waypoint at each corner, and calculate the distance between the points.

    Note that waypoints include altitude by default, but some GPS's will allow you to remove it, depending on how you want to do your "straight-line" calculation. Do you want the line to include slope in the calculated distance, or to assume that both points are at the same altitude and calculate a straight line that way? My guess is that it's the latter.

    A WAAS-enabled GPS with location averaging can be pretty close, within a few feet. My eTrex Vista CX has the features mentioned, and mapping, so you can draw your plot in a topo map, print it out, and add locations for landmarks, structures, ponds, etc. It's a fun toy and a useful tool, though I started out with the most basic model and got familiar with that first. The Vista has a lot more features to wade through.:)
  5. Drakejake

    Drakejake Well-Known Member

    Yes, ArmedBear, I want distance in a flat plane above the earth because I am trying to establish property boundaries. I assume that if the plat shows a boundary to be a quarter of a mile long, this means that the distance is a straight line on a plane above the hills. So walking the hills would give you a false distance, right? An acre, for example, consists of a flat plane above the surface of the earth, not distances following the surface. Consider a crevass which is 100 feet wide and 500 feet deep. The land included would be 100 feet wide, not 1000 feet wide, if this makes sense to anyone.


  6. ArmedBear

    ArmedBear Well-Known Member


    There's something BETTER you can do.

    Get something like the Vista Cx and Garmin's Topo software (another $100). Mark the waypoint in the field, with averaging, WAAS, etc. to maximize accuracy.

    Then, upload the waypoint to your computer, draw the property boundary on the computer map starting with the known marked waypoint. Create waypoints for the corners. Download these new waypoints to your GPS and download the topo maps to the GPS as well.

    Go back into the field with your GPS, now with a topo map in full color on the screen, and boundaries marked, find the points you downloaded, and mark them with flagging tape, stakes, etc.

    If you do it just right, you'll be really close, and the GPS with topo map will help you find your way through the hills.

    GPS's are neat!:) They do take some commitment to learning the bells and whistles. I recommend a book, too, so you understand how the thing works, especially WRT different types of topo maps, compass declinations, etc.

    I have the Stephen Hinch book, and can recommend it. Well worth the $11, to get the most from your $300 GPS and $100 mapping software.:)

  7. Alphazulu6

    Alphazulu6 member

    My Garmin GPS 60cs and Garmin Vista both do straight line +-3 feet generally. You can also do area square footage calculations on both of those and any of the better ones offered by other brands. And to beat the dead horse.... but it will be a tad off unless you do it a few times and take the running average (measure/walk it four times, add them all up, divide by 4).

    Good Luck!
  8. ArmedBear

    ArmedBear Well-Known Member

    The Vista Cx will do the averaging for you, though you have to read up on how to do it just right.

    Doesn't the Vista?
  9. Drakejake

    Drakejake Well-Known Member

    ArmedBear and other commentators,

    I have the plat with metes and bounds (distances, angles, and set curves). I do not see a fixed point on this map, i.e., a pin or physical marker or lat/long. The southern boundary is a road and so I know where that boundary is. I would like to mark a GPS point on that road and then walk up the opposite hill and know the straight-line distance between the two points. I am considering the Garmin CSX (something like that) but am not sure whether I can use it to measure between points, rather than a walked or driven route. The land is very hilly and thickly wooded. I have online topo maps and online county tax maps with the drawn boundaries. What I do not have is some way to connect something on the maps to something on the land itself. Sorry, my only training in this was as a Boy Scout many years ago.

    By this way, there is some connection between my question and guns, because this is land I just purchased for target shooting and camping.


  10. Alphazulu6

    Alphazulu6 member

    *scratches head* I havent got to that chapter yet in the three years I have owned a vista. I know it can do alot. I have never actually tested the Jumpmaster T-10 Delta parachute altimeter countdown either (I dont think I would want to be lookin at my vista while taking the plunge anyway) hehe.

    They are remarkable hand held pocket carry devices :D
  11. ArmedBear

    ArmedBear Well-Known Member


    If you can find just one point and set that as a waypoint, you can project X distance in Y direction from that point and create a new point there. Then you can walk towards it and you'll be able to see where you are WRT the new point.

    What I don't know anything about is surveying, or the sorts of numbers surveyors will give you.
  12. Drakejake

    Drakejake Well-Known Member

    Thanks, guys. I used Pricegrabber to find the best price and ordered the Garmin CSX from PCNation.

  13. kungfuhippie

    kungfuhippie Well-Known Member

    Okay, this is my job!!!!
    Surveyors use GPS to get very accurate measurements 1/100" The trick is to leave the GPS running at a point for a long period (12hrs+) this will allow it to read off of several satellites and get a more precise point. The Plat map should have a benchmark of some sort listed on it. Usually a nail, brass dish, steel or lead pipe. Everything is referenced off of this benchmark seeing as how back 100+ years ago when the USGS surveyed (or earlier than that in TN) Because it was very easy to base everything off of fixed physical points wrather than latitude and longitude. If you are doing this for curiosity, great. If you plan to use it for putting in a fence or determining what is yours, spend a few hundred and have a licensed surveyor mark you property. Then it's legally defined. Many surveyors will do this type of work and depending on the number of points (4 corners or a zig-zag property) will do it fairly cheap. If you can find a buddy who knows how to use a transverse or total station you could bribe him with some adult beverages or ammo etc. to help you out too.
  14. Drakejake

    Drakejake Well-Known Member

    This tract is 38 acres and I believe a stake survey would cost thousands. However, one boundary is a paved road and the other two boundaries are straight lines, about a half mile and a quarter mile, respectively. The tract is part of a subdivision and the plat I have is one of about eight total. I do not see any reference to a physical marker on my map.

  15. 22-rimfire

    22-rimfire Well-Known Member

    You may be able to use an adjacent parcel to find your approximate corners. I have done this and usually there is something to base your field measurements off of. Surveyors will often do this if your property has no corners marked. But to do it right or even approximate, you should probably hire a surveyor.

    Since there is a platt map, the corners may still be marked. I would spend a fair amount of time looking for the pins set for at least one of the corners. Remember, the corner along the road will not be at the edge of the road by off the road 10 feet of so. Road should have the rightaway width wmarked hich you can measure from the center line of the road. One of those deals that have the big magnet (or metal detector) will help you find the pins if they are sunk to ground level.
  16. KD5NRH

    KD5NRH Well-Known Member

    Shouldn't be that bad; we just had a 10ac rectangle done and it was under $500.

    Two points and one boundary were defined, and two others partially defined, which likely helped a lot with the price, but the remaining points required some thrashing around in briars to get to, which likely didn't do good things for the price.

    What we did, at the surveyor's suggestion, was to get our estimates with the GPS, and try to clear paths for him so he wouldn't have to spend the extra time with a machete.

    Needless to say, we missed by about 12ft on the endpoints, leaving the line about 6ft into the brush, more due to my calculations being a bit off (neglected the shift in magnetic declination since the previous survey, among other things) than the GPS being that far off.

    00 buck does wonders for trimming out problematic tree branches, BTW.
  17. kungfuhippie

    kungfuhippie Well-Known Member

    Well if you are just interested in 1/8 of the 38 acre tract (4.75 acres) you could probably have gotten those lines two surveyed for less than the GPS, though the GPS is always fun to have (and useful). Going cheap on land is like going cheap on pistols-you can really lose big for it.
  18. Bwana John

    Bwana John Well-Known Member

    Simple trig. :)

    Put GPS in UTM mode.
    Take GPS to both location.

    Call one location (1), the other (2).
    Take UTM quardinates of both locations, you will get a 2 numbers at each location, N-XXXXXXX & E-XXXXXX

    Remenber A^2+B^2=C^2?

    A=distance between N(1) and N(2)
    B=distance between E(1) and E(2)
    C=distance between the 2 points

    The final math looks like;
    (N1-N2)^2 + (E1-E2)^2 = (distance between the 2 points)^2

    (if you are not familiar with UTM, the distance will be in meters, depending on your GPS unit the error should be <3 meters)
  19. kungfuhippie

    kungfuhippie Well-Known Member

    Bwana John.
    That won't be any more accurate. Let the GPS collect info from several satellites (the $50k+ units surveyors use site for 24 hours when possible before they are considered on point) IF the unit has the batteries for it give it at least a good hour, the longer you wait up to 24 hours the more precise the reading will be. A handheld unit will never be dead on, it's like a Walmart scope: good up to it's designed limits. But getting a boundary survey, minimum should be included in the cost of buying large unmarked property. Last thing you want is to put in a fence 6" onto your neighbor's land and get sued over it. Even if you win it's expensive to fix. In my expirence lawyers cost more than licensed surveyors...And a surveyor is more fun to shoot the breeze with.
  20. 308win

    308win Well-Known Member

    I have permission to shoot on a fairly hilly but open parcel. I have often thought of using a GPS to calculate distances by taking the lat./long measures at different points. Why wouldn't this work? If I am off by a couple of yards I don't mind as the difference in bullet drop will be negligible.

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