GPS Receivers? 25
An Anonymous Coward asks: "I need a GPS receiver for some field research, and am having some trouble finding one that meets my requirements. I need to have the coordinates and time recorded once per second for an extended period (12+ hours) with a decent accuracy (5 meters or so). Ideally, I'm looking for a device which will record real-time to my Dell notebook (running Windows XP), but I'd be okay with one that recorded into it's own memory as long as I could download to my Dell easily and: a) it has enough memory to save a days worth of data or b) it will save about an hours worth of points but is cheap enough that I can get two (so I can tag-team them). I'm working on a research budget, so the solution has to be under $800 (but less is better, or course). I thought a PCMCIA card receiver might be a good solution, but it seems like the stand-alone units have more to offer, so I'm open to either option."
Handspring (Score:3, Informative)
Re:Handspring (Score:4, Informative)
the slower proc. in the Deluxe makes accuracy and tracking and pans/zooms poor by comparison- plus more batteries to consider. (i would not use the palm/gps unit combo- get a dedicated unit; I should know, i tried both- for my Palm Vx and my Visor deluxe- but still bought a dedicated unit)
for capacity and laptop compatibility- get the new Magellan Meridian Platinum $300+ retail, you can find for $264 online.
they use 8-64 mb SD cards, you can upload/download tracks to them at will, separate from the 16mb basemap of the US (the largest basemap around)- oh, and with BIOS updates, the will be able to us the 128+mb SD cards.
plus, unlike current Garmin Models (including the new 76s) when you make your track into a 'route' it uses all of the trackpoints not just 'some' so it doesn't cut corners, etc.
i have the predocessor (Magellan Map 330), but considering your budget, the SD card capability of the Meridians is the way to go (much better antenna then the garmin unit with external memory- the eMap)
go here: http://www.magellangps.com/en/products/product.as
oh, and you won't get that kind of accuracy without standing still and 'averaging' the WAAS signal with an consumer level unit (all this one supposedly is very accurate: http://www.magellangps.com/en/products/product.as
a good place for info is this: http://joe.mehaffey.com
Garmin? (Score:3, Informative)
Re:Garmin? (Score:2)
Plenty of cheap GPS (Score:3, Informative)
Based on your criteria, I don't see why you'd have any problem finding one. There are dozens of GPS's for < $200 USD that have serial output. You could (Dog forbid) even use Hyperterm to log the data to a file.
Most of the headless GPSs do not have internal batteries, but a cheap 6 amp hour 12V sealed lead acid battery or gel-cell will run it for days. The one I use in an application (which is standalone, but requires a PC board to mount it) pulls 30 milliamps. A 6 amp hour battery would run it for approximately 180 hours.
Check Garmin, Sirf, Motorola, etc. There is no shortage of lost cost GPSs
--jcwren
99 Dollar Etrex, sold at Walmart (Score:3, Informative)
If you want a little more percision then go with this [garmin.com], but the whole DGPS (less then 5 meter accuracy) thing only works if there isn't a large amount of trees or hills, it is about twice as much but comes with the cable.
Re:99 Dollar Etrex, sold at Walmart (Score:1)
i did for my garmin e-trex. to hook it to my palm 3/computer for firmware updates etc.
wrong- no more acc. (Score:2, Informative)
both have very poor reception under moderate cover.
WAAS may help, may not, but get a better antenna than any eTrex has for better accuracy.
don't beleive me? go to www.geocaching.com forums and see the complaints by eTrex owners who can't find the spots under trees (and they're talking 25m+ in-accuracies, if not total receptoin loss)
What the hell did you title mean anyway? (Score:2)
once per second? (Score:1)
I sincerely hope for your sake that the technology has gotten better.
Re:once per second? (Score:1)
Often, with a new GPS unit, the first time it is used when new (or after not being used for a long time), it will need to refresh it's ephemeris and almanac data, and determine just where it is. Especially if, say, you buy a Garmin, and you live in Australia. The last time the GPS receiver looked, it was in Kansas, now it doesn't know _where_ it is.
I've seen the little GPS-12 OEM boards take 3 or 4 hours to initialise the first time. (I'm nowhere _near_ Kansas).
Re:once per second? (Score:2)
A typical receiver will quickly locate itself -if- it has a recent almanac and is not significantly relocated since it was on last. (ie: it's best guess is close enough.).
The most extreem cases seem to be a few hours for units that have significantly out of date almanac and have been relocated significant distances. (my older Garmin suggests that a difference of 500 miles is enough to slow down initial acquisition. While I'm sure newer units are even better, this has held true for all uits I have personally seen. I've head descriptions of units being off for -years- and having run out of power (therefor no almanac) taking a few hours to aquire. Not a typical scenario. (As well, Garmin units can retrieve almanac data from another garmin unit and that will help them aquire in such circumstances, I'm sure others can as well).
Re:once per second? (Score:2)
This extract from the documentation suggests acquisition times a lot quicker than the few hours you mention:
BUY A GARMIN, Here's Why... (Score:5, Informative)
Without DGPS or WAAS you will not get readings with an accuracy of less than 5 meters more than about 60% of the time. (You could spend 5 years researching and understanding the statistics related to GPS units). Most units are specified to be within 15 meters 95% of the time. They do NOT accuratly tell you when they are NOT within that tolerance. They may give a confidence level of one type or another, but those again, are based on statistics and are not 100% accurate.
With DGPS you can have accuracies within the range you want if your in an area that can receive DGPS signals. A DGPS receiver will cost you a few hundred dollars, and the GPS you use has to be able to use DGPS information. (A DGPS capable GPS receiver will NOT pickup the DGPS signals, rather it needs an external receiver to get the signal, but it will process the data.) (You may find an exception to this, I expect it will be outside your price range by a wide margin).
WAAS might work for you, but then again, it might not. If you on the East, or West coast you will have a higher probability, but even then it has been rather spotty for many people and is really intended for aircraft (significantly above ground) usage. The satelites are too close to the horizon for most people and are blocked by ground clutter. Optimally WAAS should get you within 3 meters, but it might only increase the accuracy of the estimated error.
Note: Getting readings that indicate within a couple meters of each other for a period of days might get you an average location with a low margin of error, but again, it might still be WRONG. Some methods of determining location are known for being inaccurate but consistant. I understand ( but do not know the specifics) that Loran is known for this. In a specific location you can expect a VERY similar reading for the same spot in the future, even if the reading is off by a wide margin from reality it will be consistantly off at that location. GPS doesn't do this significantly. With the satelites moving at a high rate of speed and various objects reflecting the signal depending on the current location of the satelites the error will not necessarily be consistant from day to day, or hour to hour.
(On the other hand, the orbits do repeat and shift slightly over a period of 24hrs so a reading at 4 o'clock today will have similar satelite coverage tomorrow at 3:55, or 4:05 (not sure which off hand).
If you want more stable results try to aquire your data at night. A significant margin of error is introduced by the ionisphere and this is reduced at night.
All of the above is generic GPS information....
Now, the reason I suggested GARMIN, GARMIN GPS units support a mode which allows you to extract data required for RINEX processing. The programs which extract this data are using undocumented functions but they do work. (see: This website [fi.upm.es]) RINEX data can be post-processed and combined with external data (freely available after a delay of a few days generally) which can be used to get very accurate results. I believe the estimated accuracy for a GARMIN unit with RINEX based post processing is about 1/2 meter.
The program to collect the RINEX processable data can be run on a laptop or PocketPC connected to almost any Garmin GPS (from the older GPS12, to the newer etrex)
Don't :BUY A GARMIN, blindly, Here's Why... (Score:2, Informative)
and unlike garmin models, the 'make route (from track)' uses all of the trackpoints (memory limited)- so with your many ($44) 64mb cards, you may find that you can track for, say, 18 hours (it's a hypothetical number)- whereas with garmins, you'd need to take the laptop- b/c when they save routes to tracks on the GPSr- they don't use ALL the trackpoints (breadcrumbs) they use only some, so your get a much 'rougher' faceted travel path.
all the newer magellans can communicate detailed info with your laptop (thanks to the NMEA data stream they support)
try this: http://www.gpsinformation.net/mgoldreview/mag-gold . tm
Re:Don't :BUY A GARMIN, blindly, Here's Why... (Score:3, Interesting)
Nothing wrong with NMEA data for typical usage. I've used it for moving map displays, etc. But, to increase accuracy you need access to significanly more detailed information, which is not available from units other than Garmin for less than $1000+.
NMEA data is not the same as RINEX.
Garmin Vista (Score:3, Informative)
I have a Garmin Vista [garmin.com] (about US$300), RS-232 Cable and Cigarette Lighter plug [garmin.com] (about US$30), and Ram-Mount [ram-mount.com] (about US$20).
What a fantastic combination for driving. Tha maps (US [garmin.com] and Europe [garmin.com] (about US$175 each) rule.
I usually use NiMH batteries when walking. They last a few hours without charging. I recently used a pair of alkaline AAs for a two week trip through Europe and only had to change them once! Granted I didn't use it constantly, but I did use it quite a bit.
I use gpspoint [uni-konstanz.de] on Linux [linux.org] for saving, uploading, and downloading routes, waypoints, and tracks.
GPS Reviews (Score:1)
http://www.stormtrack.org/equip/ [stormtrack.org]
(click on Electronics)
GPS Statistics (Score:2)
You did say +/- 5m so I am guessing you do know this, but if not you may want to be sure you are getting what you think you are getting (apologies to "The Princess Bride").
sPh
I built one (Score:1)
I'll build one for you for $600.00
I built one for my own research-see the end of the PowerPoint presentation under "A Context for Assisted Cognition" on my home page" [washington.edu] . I could have made the form factor about 50% smaller if RadioShack had a better selection of project cases, but oh well...
I can get 5m accuracy (using GPS/WAAS) and can run and record data for about 3 days on end with samples every 2 seconds. All the data recording is done with a PalmPilot and you can get it from Linux or Windows.
Email me for more info.Garmin GPS-16 sensor/receiver (Score:3, Informative)
This is only a receiver, with single cable ending in a RJ-45 connector for serial and power.
I power the unit from the laptop's keyboard port (lvs == low-voltage supply), using a handcrafted converter to split serial to a Cisco-standard RJ-45 from the Garmin's RJ-45.
One feature not requested -- the GPS-16 provides a PPS output, making it suitable for use as a very accurate time source for NTP or simply for timestamping.
Accuracy (Score:1)
The other technique that could get you the accuracy you want is differential GPS (DGPS). It is based on the concept that all receivers in a local area experience about the same error. So a receiver is put at a known location and transmits a differential signal (how much error it's seeing right now). With the help of a special receiver, this signal is used by the GPS to calculate a more accurate position. Thing is, DGPS transmitters are not everywhere. The Coast Guard has put up some, but unless your in an area where the extra signal is available the only choices are to do without or to put up your own temporary DGPS transmitter while you need it.
One other option is to post process your data. You record the error at a known site while you are out taking your readings. You then apply the errors as seen to the known receiver to the field receiver readings to get a more accurate reading. Unfortunately, to do this ideally you should have a very accurate timestamp, and the data provided by the Garmin is only accurate to the second. Also, the calculations can be made more accurate if you have the individual satellite data, but units like the Garmin only give out the final computed location. It might be close enough for your use, but then again, it might not, you'll have to determine this.