which GPS for plant mapping

[metalfish]

I'm trying, unsuccessfully, to work out what kind of handheld GPS I need for accurately mapping the location and spread of rare wild plants on the reserve where I work. Does anyone have any suggestions on what I do or don't want.
I need it to be accurate to a foot or less.

[Deb London]

I saw your other post and couldn't answer this question. My experience is that they are not that accurate at all, but I've only used one TomTom and one on a phone.

There are forums dedicated to GPS etc, and if you continue to draw a blank, you could asked there.



I do wonder if you can "calibrate" any of the models available. For example, you can probably determine the coordinates for a fixed feature on your reserve exactly. I don't know whether there is a GPS available that allows you to "correct an error". There certainly should be. You could then calibrate each day, or however often you would need to.

[slimrbp]

I think even the best GPS systems are only accurate to about 15m in optimal conditions.

This will impacted by line of sight, availablity of satelites, atmspheric conditions etc. and could very day to day and hour by hour.

[Dorts]

Garmin have always been one of the leaders in hand-held gps devices. I still have one of the original 'e-trec's' which will give a map ref. to within ten feet in perfect conditions, but usually around 20-50ft.
Accuracy, as Richard has said, is down to conditions, terrain and satellite availability.
Devices range from 100-1,000 pounds depending on your needs and most now display high quality O.S. maps with greater accuracy usually coming at a price.
If you require accuracy down to 1ft. I would suggest you spend some time and create your own maps and grids, as I know many others have done in a similar position.
Dorts.

[metalfish]

thanks everyone for your responses, I think I can be accurate to within 15 m with just an os map.

Looks like the old fashioned method of using a tape measure may be it

[poschiavanus]

You should be able to get to around 3-4 metres accuracy with modern GPS (with WAAS/EGNOS enabled): particularly if you take several readings for each important point and average them (the constellation of satellites in the sky + other factors such as tree cover etc, affects accuracy). Most GPS allow you to see the accuracy when you make a reading, mine is certainly sensitive to orientation (I get better readings when it's held level). Some (not Garmins) will output this data (in the form of values called ldop and vdop) when you download to a PC.

There are techniques (pretty techie I believe) called Differential_GPS which can improve on this.

I use a Garmin for biological recording, but also for contributing to OpenStreetMap. The data collected using GPS is about the same or better than Ordnance Survey Landranger maps (see this). So I think a GPS is pretty useful. GPS really make a difference now to building local maps with the particular level of detail you need, but there are loads of other useful tools out there too, and increasingly useful datasets as well.

Obviously the most important criterion here is accuracy, and I would imagine convenience of transferring data to a PC. So WAAS/EGNOS is a must. Simple downloads usually imply a USB connection, ideally look for a device supported by gpsbabel and then you wont run into problems with poorly supported bundled software. Decent battery lifetime is very useful in the field (this is a problem for things like the GPS in the iPhone), and possibly the ability to give your waypoints a useful name. Beyond this it gets fairly technical and there is such a huge choice of devices it can be somewhat overwhelming. The one group which is not recommended are the GPS designed for in-car satnav applications: they often have a 'stay glued to road setting'.

HTH,

posch

[metalfish]

cheers posch, I'll look into this

[Cotham Marble]

Originally Posted by metalfish

I'm trying, unsuccessfully, to work out what kind of handheld GPS I need for accurately mapping the location and spread of rare wild plants on the reserve where I work. Does anyone have any suggestions on what I do or don't want. I need it to be accurate to a foot or less.

It might worth seeing if can blag a loan of equipment, (maybe offer some student participation in your survey ? ) - from UCS which does a have Wildlife Management Dept so may have dedicated software/hardware ? Wildlife Management and Conservation-FdSc (or am I embarking on a grandmother egg sucking tutorial ? )

CM

[Peter W]

I've been using a Garmin eTrex H Handheld Navigator for the last year or so. Very pleased with it, accuracy is better than 10ft in good conditions and available for about £68 from Amazon. You can spend a lot more, but you are paying for the bells and whistles rather than any increase in accuracy.

[xiaoqin001]

One person holds the optical target and reads plant labels while the other person operates the total station.