GPS hardware and software for field work

windrockwater · 03-13-06, 06:38 PM

Hi all:
i have an axim x50v and want to use it with a gps receiver connected to it and some type of software for outdoor mapping. I do landscaping and want to use it to locate large trees on a property. I need to then put that information into AutoCAD which is a CAD computer drafting program (dxf file format?).

Does anyone have any ideas on what could work for this? GPS hardware and software suggestions would be great.

Thanks. Sean

Li0rE · 03-13-06, 06:54 PM

I don't think GPS would be the best solution for you. The receivers can be off at times by 5-40 feet, which could be disasterous in mapping a single lawn!

windrockwater · 03-13-06, 07:26 PM

I have heard about some that provide accuracy up to 1 foot. That would be good enough accuracy for my purposes. I know the government allows accuracy through to about 3 feet?

marksj · 03-13-06, 07:33 PM

Originally Posted by windrockwater

Hi all:
i have an axim x50v and want to use it with a gps receiver connected to it and some type of software for outdoor mapping. I do landscaping and want to use it to locate large trees on a property. I need to then put that information into AutoCAD which is a CAD computer drafting program (dxf file format?).

Does anyone have any ideas on what could work for this? GPS hardware and software suggestions would be great.

Thanks. Sean

This thread may help you out
http://www.aximsite.com/boards/showthread.php?t=119288

SteveFLHTCI · 03-13-06, 07:37 PM

The units that provide that kind of accuracy are a lot more expensive and not typical use GPS receivers.

Li0rE · 03-13-06, 09:47 PM

I didnt have the chance to read through that whole thread, but from the few posts I did read, it seems to me the way to go is good old fasion paper, pens and measuring tape! (or one of those wheel things with a handle and you roll it and it displays the distance on a meter :))

03-13-06, 11:08 PM

You would have to get a GIS grade GPS receiver with either post processing or a correction signal to get sub-meter accuracy. While they are not cheap they are much cheaper than a surveying grade sub-centimeter setup. You can post process with some cheap receivers, but you would have to collect for at least a half an hour to get sub-meter results and you wouldn't be able to get good results from under a tree so you would have to create at least two offsets and measure to them then plot the offsets and the intersectiing arcs to locate them. and since each point could have an error of around 3 feet your intersection could easily be off by 4 or 5 feet.

windrockwater · 03-14-06, 11:11 AM

There is a company i found called Trimble that makes some handheld units. The GeoXT and GeoXH look pretty good. The spec sheet says subfoot accuracy? I cant figure out how much they would go for but Ebay has some for 2-4k.

I can certainly be content with accuracy from 1-3 feet. My goal would be to get an accurate plot plan from a surveyor that shows an existing house. Then i want to go to the property, base my points off of the house footprint, then locate all of the trees on the property. I would then return to the office, use the house points as a reference point to the plot plan, and then import/overlay the tree locations over the plot plan. The trimble GeoXH says that it can locate within 8 inces with an antenna? That seems perfect for my use??? I am reluctant to commit to buying something without knowing if it will be able to transmit the locations into Autocad readable format.

Of course, i would prefer to use my dell but if it cant be accurate enough then so be it.

03-14-06, 12:56 PM

You can get pricing here: http://store.esri.com/esri/showdetl....Category_ID=63

You will probably need something like arcpad to translate the coordinates for you.

Remember also that as I said earlier you may have problems locating trees with gps as the foliage will mess with the signal. You may want to contact a good surveyors supply store and see if they will rent you the unit so you can evaluate if it will actually work for you.

irish.david · 03-14-06, 09:13 PM

The accuracy quoted by SIRF, who make the SIRF III chipset found in most modern gps receivers, is less than 10m for an Autonomous lock and less than 5m for a lock aided by SBAS. Doesn't sound that good but these are worst case scenarios. The more satellites are being tracked, the more accurate the fix.

Dave

03-15-06, 08:05 PM

Originally Posted by irish.david

The accuracy quoted by SIRF, who make the SIRF III chipset found in most modern gps receivers, is less than 10m for an Autonomous lock and less than 5m for a lock aided by SBAS. Doesn't sound that good but these are worst case scenarios. The more satellites are being tracked, the more accurate the fix.

Dave

IMO, the more satellites that are being tracked only means that the sensitivity of the GPS unit is much better but not necessarily mean more accurate. The older GPS units (with WAAS enabled) under a clear sky is more accurate than SiRF III units (with SBAS disabled). Only when SBAS is enabled, the SiRF III units might be able to get <5m, but this is what the accuracy of the older GPS handhelds used to get already e.g. Magellan, and Garmin units which are WAAS enabled.

ccapps · 04-11-06, 11:51 AM

Hi I'm a geologist and use ARCPad with the AXIM x51v. I think it would also work witht he X50. The website is www.esri.com/arcpad7.

JakeRich · 04-11-06, 11:59 AM

Originally Posted by lawman

IMO, the more satellites that are being tracked only means that the sensitivity of the GPS unit is much better but not necessarily mean more accurate. The older GPS units (with WAAS enabled) under a clear sky is more accurate than SiRF III units (with SBAS disabled). Only when SBAS is enabled, the SiRF III units might be able to get <5m, but this is what the accuracy of the older GPS handhelds used to get already e.g. Magellan, and Garmin units which are WAAS enabled.

Lawman, you got it right. The number of satellites, above about 5, is really not much of a factor in accuracy. GPS101 and 201 both have discussions of GPS accuracy. Basically, at any given instant you really cannot depend on the fix to be much more than either + 10m or + 5M (with WAAS). However, if you hold the GPS stationary and get a lot of fixes, you may be able to average them and get slightly better. Even that averaging is not that accurate, however, as I displayed in GPS101 with the picture of thousands of fixes in the same location.

If you need more accurate fixes the only solution is to move to a GPS with more accurate clocking. You can get sub-meter accuracy for about US$15K, and for only a couple of US$Millions (and the cooperation of the US Air Force) you can get millimeter accuracy.