Looking to get a datalogger

[mfrebuilt]

Hi, I found these forums while looking for information about GPS dataloggers. I'm seeking some help in finding an affordable datalogger that will meet my slightly unusual requirements. I'm an enthusiastic skier and an even more enthusiastic nerd. I want to be able to transfer the logfile to my computer, linux preferably. I want to write my own program to display the data and report various information to me. For this reason I'd be hoping to obtain a logfile before I actually purchased any device to see if I can make sense of it.

Accuracy is one of my top priorities providing it meets the other specifications, and I need to be able to record latitude, longitude and altitude (I'm not sure how standard recording altitude is). I want to be able to take the GPS out with me all day, so it would need to have a battery life of 10 hours minimum. I'm not sure how quickly GPS dataloggers can record position but I'm someone will come along and tell me something along the lines of every second.

That's all I can think of for now, but I might think of some other questions if anyone is able to provide me with any help.

[Prodnose]

Hi, you might find this link useful:
http://www.pocketgpsworld.com/modules.php?name=Forums&file=viewtopic&t=63952&start=0&postdays=0&postorder=asc&highlight=
My own searching found no loggers at 1 second intervals - that doesn't mean they don't exist. As you will see, I use a ZyCast SG-289 which now seems to have been superseded.
On my instrument and, I think on the new version, data is recorded on a SD card in NMEA format which is a text file. Date, time, lat, long and height are all recorded. If you are not familiar with NMEA, I could supply a small file for you to try.
The fastest time I can record is at 5 second intervals. The accuracy is typical for GPS, upto +- 15 metres, but much better for most of the time. Height is slightly poorer. Again, if it is of interest, I could supply a Google Earth .kml file produced from the logger. You can then compare the track with actual paths

[mfrebuilt]

Thanks for the reply Prodnose. I did a bit of searching for a device that might have a 1 second log interval and found this site http://www.semsons.com/rorbgpsdalos.html It seemed to be everything I wanted initially, the only exception being an 8 hour battery life (I could still log for most of the day, maybe switching bluetooth off is possible and might save some power). There is one problem however, the user manual linked to on that same page says "Time Interval ... 5secs ~ 60secs, user adjustable". I imagine this would be a more reliable source, but it's also possible they recycle their PDF format and forgot to change that section or something. It would be odd for Semsons to claim that it can log every second if that is an uncommon time interval. Maybe I'm being just a little too hopeful considering it seems to be almost exactly what I want

[philpugh]

I also have the 289. The main reason for going with this is the SD card - you just unplug it and import the tracks from it (in my case into MemoryMap) and work with the information. For walking I find every 15 secs is more than sufficient. Even for cycling it's OK. I don't bother with car trip logging - I tend to stay on the roads so I know where I'm going

GPS elevation accuracy is discussed at length in this forum - but due to the nature of the system it doesn't reach the same accuracy as the horizontal fix (e.g. 10-15metres). At home (60.1 mtrs elevation) I have seen negative elevation heights with all of my GPS units over the years. I wouldn't rely on GPS elevation to do anything significant.
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Phil

[mfrebuilt]

USB is more convenient for me than an SD card because I use my desktop, which doesn't have a card reader, much more often than I use a laptop. I have heard that altitude readings aren't very accurate, but how accurate are they been consecutive readings? I'm more interested in the change in altitude than the actual altitude. Luckily when you're skiing you get fairly large changes in altitude anyway.

[Prodnose]

The SG-289 won't do what you want.
I think the altimeter would be OK. Consider buying a normal hand-held GPS. Practically every such GPS logs data as well as providing real time and navigational information. Also consider a GPS with an internal aneroid barometer as this will help with short term stability. As you want to use USB make sure that the GPS has a USB connection as some only have an old-type serial interface. Suggest the Garmin range - www.garmin.com
The cost will be higher than the SG-289 and card reader.

[Prodnose]

In writing my last reply, I had forgotten that you want to use Linux. I had originally wondered if the SD card text format might be easy to read. The data logs from hand held GPS's is usually in some proprietary format. I guess the Linux forums might contain some useful info.

[kartracer]

Have a look at the Trackstick II or Super Trackstick. I have just to-day received a Super Trackstick which I got for use while skiing and walking.
http://www.trackstick.com/

Download the software from the main site to extract the user manuals, but if you decide to get one then they can be found cheaper elsewhere, e.g.
http://www.naonline.co.uk/gps-tracker/trackstick-gps.php
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Kam

[mfrebuilt]

I was actually surprised to hear that the file format was text. I was expecting to have binary data where I'd have to find out what byte order it's in and some massive manual decoding of their protocol. If you logged 16MB of data on your GPS and then transferred it to the computer, is the file 16MB or suddenly a lot larger? I'd be surprised if the actual device stored all the information as text.. considering some of them have less than 50000 waypoints, efficient storage shouldn't of data should still be of concern to them.

[Prodnose]

Here are a couple of NMEA sentences opened in Notepad from my SD card.
$GPRMC,092143.000,A,5226.4968,N,00236.1827,W,0.00,,280108,,,A*67
$GPGGA,092146.000,5226.4968,N,00236.1827,W,1,06,1.5,313.3,M,49.0,M,,0000*40

I'm not sure how my hand held GPS stores data or the size of the files. They may well be in binary format but I've never managed to download them directly to find out. I actually use an excellent piece of software from www.gpsu.co.uk to do it for me. Here is a fragment of the output from GPSU
N52°26.4734' W002°36.1324' 1012.9 28/01/2008 09:44:10

If you want to do it yourself, take a look at this information on the Garmin web site
http://www8.garmin.com/support/commProtocol.html
If you succeed, please tell me how to do it!

[mfrebuilt]

The file format looks incredibly easy to read. The only thing is, although the datestamp is clear, I can't see the timestamp there. I'm quite confident I'll be able to get the timestamp out after I take a closer look at the protocol. Also, about your last comment about telling you how to do it - are you a programmer? When I get around to it I'll be doing everything in C and I can send the source code to you if you want. Initially I'll just be making some simple things to make sure it's all working, then I'll get to work on the big project later after I've learnt a bit more about 3d graphics in OpenGL.

[mikealder]

Have a read through This document, skip the rubbish at the start and you will find a more detailed breakdown of what the NMEA codes actually contain and their breakdown.
A simple parse of the text string is all that is required to grab the information you need, $GPRMC contains the time stamp (along with a few other parameters, see section 4,2,2 for information on UTC) - Mike

[Prodnose]

The date appears in $GPRMC and is 28/01/08. Height appears in $GPGGA between commas 9 and 10. Lat and Long are in the form of degrees and decimal minutes. There is no space or other separator between degrees and minutes. A quick search using Google will find plenty explanations of NMEA. Normally this is the format in which GPS receivers send info to mapping software etc. The SG-289 data logger saves it in this form.

All but the most basic of hand held receivers can supply NMEA data via a serial link. The data is (substitute "are" if you must) sent continuously with no form of handshaking. As I said previously, they also store a track log which can be downloaded via the serial link. It is not then sent as NMEA. What I can't do is to send the request to send and acknowledge codes to get the stored data whatever form it is in. Because I can use someone elses software to get it for me I've backed off from making the effort.

I can only programme in VB but I can sometimes extract bits from other languages - a bit like my reading with my school boy french. If you decide to tackle the downloading of stored tracks from a Garmin GPS I should be very interested.

[mfrebuilt]

So the 092143.000 was the time. I was a little thrown out by the .000 since it seems odd that they'd have an accuracy in milliseconds if it can only log once every 5 seconds at best. Although the format is easy to read, it's a bit silly. "092143.000," and "280108," are the time and date stamps respectively. It's just taken 18 bytes to store that information. You could store the number of seconds since January 1, 1970 in 4 bytes and it would hold until past the year 2100. Not to mention that some of that data is recorded twice. I really hope the GPS doesn't store it in that format on it's own storage device.

[philpugh]

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