Holux M-241 GPS Logger

[ATJ]

Greg, obviously it was only a short time between today's logging with the Holux and yesterday's. This would give little time for the internal clock of the Holux to get out. When was the last time you used the Holux before yesterday? i.e. how long was it since it last was able to set the internal clock?

[Mr Darcy]

Last time I used the Holux was about a month ago. Not using that computer, so cannot check exactly.

HOwever I don't think that's the issue. As I said, the FIRST thing any GPSr does after finding a satellite is correct it's internal time. The clock should be right before it starts logging a track. I think the real issue was poor seeing due to the heavy cloud cover (largely absent yesterday.) coupled with poor geometry of visible satellites. Remember the house is in a hollow. You can see the creek it is hard against (Line of trees). There is quite a high steep hill immediately on the other side of the creek. The corner of Falls Rd and Armstrong St is about 50m higher than the house. That will block any view of satellites low on the horizon to the North and West.

[photohiker]

I believe the satellites are geostationary. I can't see how GPS could work any other way. I suspect that the inaccuracies seen here are to do with the number of satellites in contact. The more there are, the more accurate it will be.

I find mine is more accurate the longer it has been running, suggesting more satellites helps.

One of the missing pieces not mentioned yet is the ephemeris data. The GPS sats transmissions start with the time from their internal atomic clocks, and this is followed by ephemeris data (precise orbital data) and almanac (the general system health and rough orbits of all GPS satellites). Transmissions are broadcast every 30 seconds and are 30 seconds duration. Ephemeris data is updated every 2 hours apparently, I haven't discovered how they account for decay, perhaps the age of the data is one of the reasons the GPSr switches between available sats. (conjecture on my part)

wikipedia: "The time needed to acquire the ephemeris is becoming a significant element of the delay to first position fix, because, as the hardware becomes more capable, the time to lock onto the satellite signals shrinks, but the ephemeris data requires 30 seconds (worst case) before it is received, due to the low data transmission rate."

Michael

[ATJ]

HOwever I don't think that's the issue. As I said, the FIRST thing any GPSr does after finding a satellite is correct it's internal time. The clock should be right before it starts logging a track.

Not with the Holux. One of it's "features" is that it can be told to start logging before it can even lock on one satellite. I get no reception on the ground floor of hour house, but if I tell it to start logging, it will. The results will be rubbish.

[ATJ]

HOwever I don't think that's the issue. As I said, the FIRST thing any GPSr does after finding a satellite is correct it's internal time. The clock should be right before it starts logging a track.

Not with the Holux. One of it's "features" is that it can be told to start logging before it can even lock on one satellite. I get no reception on the ground floor of hour house, but if I tell it to start logging, it will. The results will be rubbish.

OK... it appears I may have this wrong. I know that when I first got my Holux (around 2 years ago) it would definitely start logging before it got a fix. I just tested mine again and now it appears to only start logging after it gets a fix. I know I have applied at least one Firmware upgrade so that may have changed it or perhaps there is a setting that I changed. I'll keep looking.

In the course of my testing, I did find out that the internal clock does get way out. I hadn't used my Holux for at least 2 months and the clock was out by either 5, 15 or 75 seconds. I'm kicking myself that I didn't write the times down to know how far it was out. While in my study (no connection to satellites) I compared the time on Holux to the time on my watch. The seconds portion was out by 5 seconds. I then took the Holux outside and in 30-60 seconds, the time on the Holux changed such that the seconds were now different by 10 seconds. Because I didn't write it down, I don't know which way they were out, so it could have been a change of 5 seconds or 15 seconds. I then realised the minutes were out by 1 minute as well, so perhaps the Holux was out by even more.

Once outside, it took 5-10 minutes to get a fix. Once it got a fix. it was fairly accurate, but improved over time to the point that it was within a couple of metres of the correct location.

Now, if there is some way that it starts logging immediately (as I know it used to), then the clock being out and the time to get a fix would definitely play into its early accuracy. Even when it did get a fix, it took a few minutes to get accurate.

Note that I did a subsequent test and it was less inaccurate at the start, but didn't seem to get the same accuracy in the end, so there must be other factors at play.

[Mr Darcy]

I know I have applied at least one Firmware upgrade so that may have changed it or perhaps there is a setting that I changed.

One of the fixes was definitely to fix corruption at Power On/Power off. I know mine goes into "GPS Searching" mode until it gets a lock, then it goes into "Tracking" mode. Sounds like the same behaviour you are seeing now.

Once outside, it took 5-10 minutes to get a fix.

This is a normal, or even fast fix for a cold start. and is consistent with what I see.

The more expensive units keep an internal sky map & timer running so they can get a fix almost instantly in most situations. It was actually what tricked me into getting the Oregon. My old 12XL stopped seeing ANY satellites even after 30 minutes at a time several times a day for several days. I thought it was because the receiver was dead, so I bought the Oregon as the 12XL was too long in the tooth to be worth repairing. It started working again after I did a "Cold Fix" not long after buying the Oregon. It turns out that the internal backup battery was so dead, the internal clock had stopped completely, so none of the satellites it was expecting were in the sky, so it didn't find any. When I did a full cold start (Previously I had told it where I thought it was), it stopped assuming what was up there & just looked at what was actually there. 20 minutes later I had a fully functional GPSr again.

[muzz]

You guys have done a heap of work on this thread - I appreciate the info I've gleaned so far. One simple question though - would you buy a Holux as a photologger for occasional use on photo treks given what you now know (cost-effectiveness is an issue)?

Cheers, Murray

[ATJ]

would you buy a Holux as a photologger for occasional use on photo treks given what you now know (cost-effectiveness is an issue)?

Yes. Well, I'd buy one as a GPS logger.

[Mr Darcy]

One simple question though - would you buy a Holux as a photologger for occasional use on photo treks given what you now know

Absolutely.
I play a game called Geocaching, where you hunt for a "treasure" at a specific location. It is often in a "different" place, smetimes because my GPSr is off on the day, sometimes because the hider's GPSr was off when he hid the object, sometimes both. So I was aware that a GPSr will not always give an accurate location before I bought my Holux.

As I think I said earlier in the thread, I have some photos that I do not even know what country they were taken in. Using the Holux and Geosetter, I will always know the location of a photograph within a kilometre, and usually within a few metres. Both are more than good enough for my purposes. If it is a photo of a rare and tiny specimen that I need to send a team out to find later, it may not be enough on its own. That is when the Oregon and its waypoint averaging comes in.

However, The $600 Oregon stores 10,000 points in a track log, while the $70 Holux stores over 131,000 track points. At one location every 5 seconds, that's over a week of logs, compared to something less than a day for the Oregon. By turning it off overnight, I used the Holux every day for a two week holiday in New Zealand, and after the trip, every photo was tagged more than accurately enough for my needs. I did move a couple as Google Earth allowed me to correct the location ("I know I was standing at an intersection, but the log has me in the middle of a paddock. Ah there it is!")

Further if I change the track point setting out to every two minutes (the maximum), it is good for 6 months without a return to base. That interval is still good enough for most photography. Think about it, even if you are driving, you will probably stop the car, get the camera out, get out of the car, frame the shot, take the photo, put the camera away, get back in the car. If you can do that in less than 2 minutes, you are doing very well. If you are walking, and looking for photo ops, camera at the ready, you will probably only move a hundred metres or so between points, and it will average between two points anyway.

[muzz]

Thanks again for your information, opinions and advice. I can pick one up off ebay for around $65 so it seems like a good price for what I want to use it for. Cheers.

[Mr Darcy]

Great. I am sure you will be very happy with it.

One thing to keep in mind when you use it is that both Camera and GPSr must be set to the same time for GeoSetter to do its stuff.
Take the Holux outside to get a fix, then set the camera to the same time (and timezone!) that the Holux shows.
The more accurate you get this the better the results you will get.

[CraigVTR]

My m241 arrived in the mail this morning, bought from Semsons & Co. Inc. (through Yahoo! Store Order System) [info@semsons.com] on Wednesday afternoon.

I have fired it up, have a fix, done some recording with it in the house, downloaded and created the kmz file all with the supplied software. Verrrrryyy easy to do.

[CraigVTR]

Went for a walk this arvo to try out the Holux and here is the result.


Thank you Mr Darcy. I have found it very easy to use but it may have improved software and firmware compared to your version. FW & HW Version [ V1.12 ][ V02] Software 0.0.0.41

[ATJ]

I have found it very easy to use but it may have improved software and firmware compared to your version. FW & HW Version [ V1.12 ][ V02] Software 0.0.0.41

Are you on a Windows or Mac machine? Greg's problem is he's using a Mac and the software support is limited. I've been using mine on a Windows PC for nearly 2 years and, like you, I find it very quick and easy to use.

[CraigVTR]

I have found it very easy to use but it may have improved software and firmware compared to your version. FW & HW Version [ V1.12 ][ V02] Software 0.0.0.41

Are you on a Windows or Mac machine? Greg's problem is he's using a Mac and the software support is limited. I've been using mine on a Windows PC for nearly 2 years and, like you, I find it very quick and easy to use.

Windows xp. I have never owned anything Apple until I bought an Iphone last month. Great phone.

[Mr Darcy]

Greg's problem is he's using a Mac

Other people tell me I have other problems
I am running 1.12FW. Don't know about the other numbers. Don't care . It works well with the BT747 S/W