gps help

[cutter88]

just purchased a Magellan explorist 310 anyone no anything a bout it... plan on using it tto mark property lines and skid trail layout? any pros and cons or info would be a big help

[jd_odell]

I do not have any experience with that particular model of GPS; however I have 20+ years experience w/GPS operations & instruction.    The most accurate GPS I have experienced was military (encrypted) and it had 1 meter (3.28 ft) accuracy.  The GPS accuracy indicates you are within XX distance of the coordinates you input (way-point) or the coordinates displayed on your GPS (current location).  So, imagine a bubble over where you are standing, and the GPS is indicating that you are somewhere inside of that bubble (UP, DOWN, ALL AROUND).  I'm thinking that a civilian GPS might get you to within 15 feet of a coordinate you input into the GPS.  To check it out, go outside your house (w/GPS) and stand out at a location that is easily identifiable on Google Earth (intersection of your driveway and the road you live off).  Write down those coordinates (I use LAT/LONG in DEG.XXXX format).  Enter those coordinates into Google Earth and fly there to see how close you are on Google Earth to where you were standing.  I'm thinking a civilian GPS will get you close on the trails, but I seriously doubt it will get you close on property lines; not close enough that I would want to say with any certainty "this is mine and that is yours".

[Mark Wentzell]

A consumer grade gps unit is not accurate enough to locate property lines. Not sure if that unit will display PDOP or not but that can be a real help in determining how accurate the unit is. PDOP stands for position dilution of precision and is basically a measure of how many satellites are overhead and in what position they are in. Lower numbers are better and 7 is generally the maximum you will want.

There's a very useful program called DNR garmin that will convert waypoints into lines and polygons for use in mapping software. I'm not sure if it only works with Garmin brand units or not.

On a good day you should be able to get within 5 meters of your position. If your unit allows you to change how positions are averaged and how long they are averaged for. Basically you can set it up to take a gps position every five seconds for 30 seconds or a minute while you stand over the point. The machine then takes the average of those positions and comes up with a more accurate point. When we were doing LIDAR plots last year the surveyor averaged the position of the plot centre for about 15 or 20 minutes but that was with much higher grade GPS units.

[ahlkey]

What handheld GPS could be used for marking waypoints down a property line?  Most often I find a corner survey point but then the owner wants an approximate line down a 40 or 80 etc.... I always inform them to get a survey or an agreement with the neighbor first. However could you rent or get one of those submeter units from Trimble and be reasonably close?  I realize under the canopy it may not be as accurate but I believe using an external antenna would increase accuracy?  It would seem a meter or two even if "unofficial" would be close enough for an approximate line for most owners and neighbors to agree on.  It probably is expensive equipment but so is the hassle and lost hours.  Thoughts?

[Mark Wentzell]

I wouldn't put my neck out on anything to do with property lines unless I was a licensed surveyor. If I were a landowner  I wouldn't want anyone laying out my property lines who wasn't a surveyor. I've never run one of those survey grade gps units but I would imagine they have a pretty steep learning curve, and most  require mapping software to view the data on your computer, which is expensive and has its own massive learning curve and it's not something you can buy once in your lifetime and just forget about it, you'll likely need to update every few years, same goes for the gps unit. Unless you're using this equipment every day then it is not worth owning.