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new here from ohio!

Started by shec6135, February 05, 2011, 06:32:12 PM

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I think previous posts have mentioned using GPSMapEdit to convert track points into line features; then into an overlay/transparent mapset which works with any other mapset(s) they have on their GPSr.  jbensmen should be able to provide more details as he converts tracks to lines for his 'my trails' mapset. 
FYI - consider any/every position your GPS gives to be accurate to +-20 feet, maybe less, maybe more.


thanks boyd for the good info!


thanks maps4gps for the info as well. i had my WAAS satelite capabilty turned off so i know it's within 10/14ft+/-


Even with WAAS on, you cannot know you are within 10/14 feet.  You could be-but GPS are not that accurate all the time. 


"According to the FAA's web site, testing of the WAAS in september 2002 confirmed an accuracy performance of 1-2 meters horizontal and 2-3 meters vertical throughout the majority of the continental United States and portions of Alaska"

this is right out of the manual that came with my gps. now i live in ohio (the southern part) but even then the hills around here are no taller than 900 ft above sea level, there are lots of satelites to be picked up and no hills capable of throwing off the gps at a measley 900 ft. now i can agree that it's not going to be EXACT, but do you really think that in 9 years they've gotten less acurate at what they do?lol i mean common, don't we all strive to get worse and worse at what we do, if this was so i think we would have reverted back to being neandrathals a lot quicker already.

i don't hunt right on the property lines for obvious reasons so 2-3 meters is certainly accurate enough for me.


So did you mean to say with WAAS on? YOu said it was that accurate with it off.

While most of the time WAAS is real good, your GPS can be off and you not know it.

You also need to remember accuracy of your GPS is not the only accuracy issue.  The source of the boundary can be off.  Some of the source data can be survey grade accuracy and some can be a good guess or a trace from a paper map.  For my landownership maps, amny times I combine boundaires from different sources and when they share boundaries, they rarely match perfectly.

Then Garmin maps have resolution issues.  They don't draw the boundaries at the exact location provided by the source file.  There is a 24K gride at the most accurate zoom level.  So the boundary is drawn along the grid not its actual location.  So this also introduces accuracy issues. 

With 3 sources of accuracy issues, I would say stay at least 50 feet from where the bounday shows unless there is something on the ground showing the actual bounday (which could also be off)


I wrote about the limits of Garmin's map format here:,1335.0.html

Not much of an issue to the intended uses of a consumer unit, but definitely a problem if you are trying to "survey" something. 32 bit coordinates just aren't accurate enough for that.


i agree with what your saying jben but i found a corner stake where my neighbor had his property surveyed and used the measure distance tool to go all the way around my property. it's not exactly square but it's self checking when you get back to the start point with all the measurments from the plot map working out and in between waypoints leads you right along some fence rows (within 5 ft) you can average in the cordinate multiple times for that corner stake as well, but like i said before it is good for you to point these things out to someone who doesn't know what they're doing, i GOT thanks anyways. -shaun


surveys are acurate to the fraction of a foot. i'm a deer hunter, i don't need all that... i did base my starting point off a corner marker, but as long as i know within a couple meters like i said i'm a bowhunter, and deer run on average 50-100 yards after the shot so i'm not going to be hunting the property line. but my route did lead me within 1 meter in places of fence lines as well, i am TICKLED PINK with my new gps!lol thank you guys for your concern. -shaun


While what you did is probably sufficiently accurate, if have a survey point, you could use waypoint averaging over multiple days to get a real good reading of its location.  (Maybe there is a way to get a lat and long from the survey which would be even better.)  If you knew the distance and direction of your corners from the marker, you could project waypoints to the corner and then draw a line connecting the waypoints.

A friend of mine wanted her property marked on her GPS.  The plat map showed where the boundaried were in relation to the section lines.  So I drew the boundary on the USGS map based on the section lines in ExpertGPS.  We found multiple old fence lines within about 50 feet of where the GPS was showing the boundary.


jben, you found and old fence (that was the actual border) and the gps was showing 50 ft off of that? i'm sure trees and things can move gradually if on a steap enough hillside, coupled with the fact that fencelines are never really that accurate (old ones anyways). i did find a stake on one of the back corners that was 15-20ft off of what my gps was telling me was the actual corner. so since it benefits me i think i'll take that neighbors word for it!lol this back corner of our propert i have never hunted b/c this guy is a lunatic and i wasn't sure about the property line back there, i never would have found this stake if it wasn't for me getting a new gps! i have never been so pleased. i can see why you guys take so much enjoyment in this hobbie, why are there only like 600 memebers here? i don't understand it, is it some kind of secret?lol thanks again -shaun


i was also wondering about downloading more of the maps from mapsource onto my 60csx. if i add quadrants from the same map that i took specific quadrants from the last time, will it erase my waypoints, or is there anything i should know before hand? i wasn't sure how many states my 8gb micro sdhc card would hold so i only did a portion on southern ohio (the parts with state game land), would an 8 gb card hold all of OH, PA, and WV as well? the map is the N.E. USA part 3 map. thanks in advance -shaun


Waypoints, tracks, routes and maps are all separate kinds of data. Changing the map will not affect them as long as you only check the map option in the send dialog box. But sending a new map will replace any existing one on your GPS.



A note on accuracy-  I am a Forester/Land Surveyor and have had the opportunity to check the accuracy of my Oregon 550 compared to an $8000 Javad Triumph unit.  With one 2 minute sample on the Oregon I was within 6' of the Opus-corrected State Plane point of the Javad.  On another occasion (and a different point) I was within 12'.  Accuracy changes with the satellite constellation (and number of samples) but I thought these results were fairly impressive for a hand-held unit.  The Oregon has an excellent averaging routine and allows returning to point at a later time to add samples to a waypoint average.