GPSr bakeoff anyone???

From another thread:

CaptCaper said:

I'd like to get together with you for a short hike and compare the two tracks afterwards just to see how sensitive this X really is. If your interested let me know.

Capt.

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Great idea, I am retired and live up north so almost any day will do with some notice.

I wonder whether there is any interest in a multi-GPSr "bake-off"? Several hikers, each with his/her unit, recording tracks and then comparing them. We could end up at my place 9and might perhaps find a few beers there) and download tracks from those devices which have a USB connection (my computer has no serial port).

Actually my old computer has a USB to serial cable and drivers that used to work, if there is any interest I can fire it up and test it out.

I can do Fridays, Saturdays and Sundays.

I might be interested in joining in.

If we want to perform some meaningful experiments, we will need to set up minimal pairs--eg:
* 2 units of the same model, 1 with an external antenna, 1 without
* 2 units of the same model carried in different locations (or external antennas in different locations)
* 2 units of differing models but the same antenna configuration.

So, the greater number of GPSes, the greater number of minimal pairs. (And, of course, a single GPS can be in more than one minimal pair.)

Also an out and back hike in a range of GPS conditions would be desireable. Since we have no absolute references (unless someone wants to bring a professional DGPS unit with sub-meter accuracy...), the best we can do is compare the in and out tracks for each unit. It might even be better to do the same hike twice so we could compare tracks going in the same direction. (Unfortunately, the satellite constellation will be different at different times.)

A hike like Depot Camp to Greely Ponds and back might be a good choice. Mostly treed terrain ranging from a fairly wide horizion to a fairly narrow valley. And short enough to do twice.

I have a laptop with both USB and serial connectors and cables for the Garmin 60/76 series and the Garmin eTrex series. Software: Garmin Mapsource, NG TOPO!, gardump (outputs the tracks in a simple text format), and gpsbabel (converts between data formats).

Doug

I would be very interested in joining in and learning more but my availability may be a problem - I am in Boston working during the week and in Bethlehem NH most weekends which often includes Fridays-

I use a Garmin 60 CS with an external antenna. Software includes Garmin Mapsource, NG TOPO, and Ozie explorer (I scan the AMC topo maps into Ozie since they are up to date with more detail.)

Maybe over the long Columbus weekend?

Doug- I have not heard of gardump or gpsbabel so I googled them-they look interesting but I am not sure how I would practically use them, especially gpsbabel. I usually just download my data from my unit into each individual software program and save within each format-does gpsbabel serve as a generic database to store info and then upload to whatever program you want to use it in??

Marty

Great idea, Mohamed! I suggest that we do this GPS test along the Owls Head (just kidding!). But, really, I would like to enter my Garmin Etrex, if the scheduling works for me (I forget the model number, but will get back to you).

Whoops, I left our the word "ridge" following Owls Head.....

Mohamed Ellozy said:

From another thread:Great idea, I am retired and live up north so almost any day will do with some notice.

I wonder whether there is any interest in a multi-GPSr "bake-off"? Several hikers, each with his/her unit, recording tracks and then comparing them. We could end up at my place 9and might perhaps find a few beers there) and download tracks from those devices which have a USB connection (my computer has no serial port).

Actually my old computer has a USB to serial cable and drivers that used to work, if there is any interest I can fire it up and test it out.

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Any day is good with me as well guys. This week is bad. Sat. Oct. 8 is out as well.
I can't do anything long and with a lot of gain right now as I'm just coming out of orthroscopic knee surgery. Just did Sugarloafs and Indian head last week. Mostly I'm out of shape big time from sitting all summer.

zman said:

Doug- I have not heard of gardump or gpsbabel so I googled them-they look interesting but I am not sure how I would practically use them, especially gpsbabel. I usually just download my data from my unit into each individual software program and save within each format-does gpsbabel serve as a generic database to store info and then upload to whatever program you want to use it in??

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Gardump is for Garmin GPSes and Unix/Linux only. Handy for up/down-loading tracks and waypoints from/to a simple text file format.

GPSBabel is multi-GPS-vendor and multi-os. For translating between file formats. (Tower of Babel...) Includes generalized text formats. http://www.gpsbabel.org/

Both are GPL.

If someone wanted to write a program for analyzing tracks, GPSBabel might be useful for converting a track file into a format that is easy for the program to read.

I can download the tracks for Garmin GPSes with both Garmin Mapsource and NG TOPO! and share them with others via email.

Doug

There will never be a date when we all can make it. So, Mohamed please pick a date and put it in trips and events. I think it should be a time when both you and DougPaul can make it.

Paradox said:

There will never be a date when we all can make it. So, Mohamed please pick a date and put it in trips and events. I think it should be a time when both you and DougPaul can make it.

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Uh-Oh! Sounds like someone is trying to draft me...

Proposal:
* We pick the best weather day of this weekend (looks like Sat). (We want to keep the gear dry--rain will confuse the experiment. Also best to still have some leaves on the trees.)
* Core group: Mohamed, Paradox, and Doug (me). (Others welcome.)
* Core GPSes: 2 60CSx, 2 60CS, 2 external antennas. (Other GPSes welcome--the core group can provide the core gear.) 1st GPS of each type used with a top-of-the-head external antenna, 2nd carried on a pack shoulder strap.
* Hike Depot Camp up to Greely Ponds and back. Once or twice. (A short hike with a range of GPS signal conditions, ranging from fairly easy to fairly difficult.)
* Record and share tracks.

(Note: the 76CS[x] is essentially identical to the 60CS[x]. We should be able to use them interchangably.)

* We can link in other GPSes types to the study. At a minimum, it would be desirable to have 2 of each--1 with an external antenna, 1 without. Additional GPSes of each type and antennas can be used to evaluate other GPS carrying locations and/or external antenna locations.
* I have an eTrex Vista (a good one... ) with an external antenna which I can add to the study. A 2nd or 3rd would be nice. (Paradox can bring his bad one )

I have a laptop with RS-232 and USB ports and cables for Garmin USB, 60 series RS-232, and eTrex RS-232. I have Garmin and NG-TOPO! (NMEA protocol RS-232 interface--should talk to most GPSes) software for recording tracks.

We will not be able to evaluate the absolute accuracy of the GPSes, but we will be able to compare the in and out tracks of each GPS to estimate the repeatability. And, of course, we will be able to compare the tracks between GPSes.

Mohamed? Paradox?

Doug

As an “other invite” I am glad someone is taking charge of pulling this together. I have plans to hike Lafayette and the ridge with my daughter Sat & Sun- I would vote for the following long weekend since I would enjoy participating ….in any event, I look forward to reading results and observations if it happens this weekend

Marty

zman said:

As an “other invite” I am glad someone is taking charge of pulling this together. I have plans to hike Lafayette and the ridge with my daughter Sat & Sun- I would vote for the following long weekend since I would enjoy participating ….in any event, I look forward to reading results and observations if it happens this weekend

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I have a prior commitment on the long weekend. Also people are likely to want to do bigger things on long weekends--this is just a single day event.

Doug

DougPaul said:

Uh-Oh! Sounds like someone is trying to draft me...
Proposal:
* We pick the best weather day of this weekend (looks like Sat).
Mohamed? Paradox? Doug

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Let me clear it with the wife, and I will respond to this thread tonight.

DougPaul said:

We will not be able to evaluate the absolute accuracy of the GPSes, but we will be able to compare the in and out tracks of each GPS to estimate the repeatability. And, of course, we will be able to compare the tracks between GPSes.

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While this is interesting, I am trying to figure out exactly what it is going to show. You will not be able to compare it to an absolute point or path. Plus you will have issues with sat acquisition and differences in the sats and times that the tests were being done. A whole slew of problems. Like you said it will not evaluate absolute accuracy. Would you be better off, maybe, just using the all the different GPS's at the same known mark or at the same location at the same time. Having all of them save its data for an hour or two and comparing its wandering around that same point against all the other systems data. Wouldn't you?

I would love to be involved in this and will be in NH this weekend but will probably be tied up so I cannot commit. I do have an old 12XL that I would be willing to loan as a really poor baseline system if I can get it too someone. That is NMEA compatable and can use an external antena. If I am able to go I would bring my Vista C also.

Keith

SAR-EMT40 said:

While this is interesting, I am trying to figure out exactly what it is going to show. You will not be able to compare it to an absolute point or path. Plus you will have issues with sat acquisition and differences in the sats and times that the tests were being done. A whole slew of problems. Like you said it will not evaluate absolute accuracy. Would you be better off, maybe, just using the all the different GPS's at the same known mark or at the same location at the same time. Having all of them save its data for an hour or two and comparing its wandering around that same point against all the other systems data. Wouldn't you?

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I was going to write a little dissertation on testing methodologies, but decided I didn't have adequate time. 3 come to mind:
1) Place GPSes at a bunch of surveyed points (sub-meter accuracy required) and record data for at least several hours at each, preferably 24 hrs. (The satellite constellations repeat every 23hrs 56min.) Don't have any surveyed points. (There are federal GPS testing ranges in the PNW for just this purpose. http://www.fs.fed.us/database/gps/gpsusfs.htm)
2) Place the GPSes at each of several test points for several hours each. (Again 24 is best.) We can compare location spreads and distance between average locations for each GPS.
3) Take the GPSes on a group hike and compare tracks. By hiking as a single group on a single path, we will all encounter the same signal conditions (GPS constellation, multipath, etc). We can also investigate the effects of diffenent ways of carrying the GPSes and antennas. The intent is to set up a bunch of minimal pairs (2 GPSes/antennas that differ in only 1 aspect, such as antenna location).

We can't do 1, 2 has to be done all at each location at the same time if we want to factor out the environment and is not a good way to address the methods of carrying the GPS and antenna. IMO, 3 is probably best for a 1 day effort by a bunch of hikers. 3 is also an attempt to evaluate the GPSes as a hiker would use them in a range of signal conditions. We could perhaps include a point or two of method 2.

Strictly speaking, there is no objective numerical method of comparing tracks. (There are such methods for comparing points.) I have thought of an algorithm which I think will work well enough. (Don't want to try to explain it on a BBS or email--voice or in person would work a lot better.) Eyeballing the tracks alone may be highly informative.

I would love to be involved in this and will be in NH this weekend but will probably be tied up so I cannot commit. I do have an old 12XL that I would be willing to loan as a really poor baseline system if I can get it too someone. That is NMEA compatable and can use an external antena. If I am able to go I would bring my Vista C also.

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If all the pieces fall into place and you can come, I (we?) would be happy to have you along. However, we may risk being thrown in the river by the others if we get too technical too often...

BTW, it is possible to get phase information from a 12XL (eTrex Vista too, IIRC) using an undocumented protocol and use it for high accuracy DGPS. Requires the GPS to be at each fixed location for an hour or so.

Doug

I have permission to be there on Saturday 9/30/06. I prefer early, around 7 am, but I live very close by, so I can be very flexible. Question: Where is Depot Camp? Is it off the Kanc or Tripoli Road? Do you have GPS coords ?

Also, I agree that only methodology #3 is particularly doable for the resources we have. Also, it employs conditions likely to be found by the average GPS user.

I would love to be involved in this experiment, but I do not have a GPS of my own and will be in Mass for the weekend.

I have always been interested to see how different GPS units' positions would compare when used at the same time over a known point such as a USGS disk. I may be able to find some survey control points for anyone interested in trying this out.

At my work we use Leica 500 series GPS equipment which has centimeter accuracy when the data is post processed or using real time corrections from a base station set up over a known point.

Paradox said:

I have permission to be there on Saturday 9/30/06. I prefer early, around 7 am, but I live very close by, so I can be very flexible.

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I have a ~3hr drive and hate getting up early...

I prefer to meet at Mohamed's or the trail head around 9am.
It's a short hike.

Question: Where is Depot Camp? Is it off the Kanc or Tripoli Road? Do you have GPS coords ?

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The parking lot at the end of Livermore Rd. Off Tripoli Rd.

GPS coords? Me?

First qualification test--if you can't navigate well enough to find the parking lot, we don't want you... (Although if you have a nice shiny GPS to contribute, we might reconsider.)

Doug

kltilton said:

I have always been interested to see how different GPS units' positions would compare when used at the same time over a known point such as a USGS disk.

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Don't really need a known point to compare the GPSes. Method 2) will show the differences. (Just won't show the group systematic error.)

I may be able to find some survey control points for anyone interested in trying this out.

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How accurate are the survey control points? Sub-meter accuracy would be nice and centimeter would be even better.

At my work we use Leica 500 series GPS equipment which has centimeter accuracy when the data is post processed or using real time corrections from a base station set up over a known point.

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Can you bring it?

Doug

DougPaul said:

I prefer to meet at Mohamed's... around 9am.

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Sounds great! Anyone heard from Mohamed? I wonder what he has in his fridge?