If Ya Like Numbers.......

[planewood]

While watching my favorite lawyer show on TV tonight I let my 60cx track for 1 hour in 10 second intervals. This was in a 2 story house with the weather outside overcast and pretty humid. I had solid bars on about 8 sats with no bar showing more than 50% and 3 or 4 showing about 20% in height. Stated accuracy during the hour was about 22'. I did not have an external antenna connected.

 

After it gathered about 300 points, I downloaded the UTM track coordinates using USAPhotomaps then imported them into an Excel spread sheet.

 

The chart below shows the ranked distance between the points and the averaged coordinate. As you can see, the great majority of the points were within 5 meters of the average.

 

I calculated the Standard Deviation (~4.0 meters) and threw out all points more than this above the average (~5.75 meters). By throwing out all these most anomalous points, the recalculated average coordinate was 1 meter away for the overall average! The actual accuracy of the weighted average coordinate seems to be about 4 meters west of where it should be. Oh yeah, the furtherest point was 25 meters away from the average.

 

To me, this is a testament to the high quality of the Garmin 'x' series! This also indicates to me that the simple average is just about as good as a weighted average.

 

Edited April 26, 2006 by planewood

[+timk54]

While watching my favorite lawyer show on TV tonight I let my 60cx track for 1 hour in 10 second intervals. This was in a 2 story house with the weather outside overcast and pretty humid. I had solid bars on about 8 sats with no bar showing more than 50% and 3 or 4 showing about 20% in height. Stated accuracy during the hour was about 22'. I did not have an external antenna connected.

 

After it gathered about 300 points, I downloaded the UTM track coordinates using USAPhotomaps then imported them into an Excel spread sheet.

 

The chart below shows the ranked distance between the points and the averaged coordinate. As you can see, the great majority of the points were within 5 meters of the average.

 

I calculated the Standard Deviation (~4.0 meters) and threw out all points more than this above the average (~5.75 meters). By throwing out all these most anomalous points, the recalculated average coordinate was 1 meter away for the overall average! The actual accuracy of the weighted average coordinate seems to be about 4 meters west of where it should be. Oh yeah, the furtherest point was 25 meters away from the average.

 

To me, this is a testament to the high quality of the Garmin 'x' series! This also indicates to me that the simple average is just about as good as a weighted average.

 

 

Pass the Asprin please.

[dusee]

your analyses are correct on paper

 

but it is a bit strange to use a gps at home were you now every inch.

And what do you want to prove?

 

The sirf III application is ment for finding your way in extreme difficult conditions.

Drift and reception don't mean a thing; does it point in the right direction when you need it.

There is also a comparison with the Explorist 600 which looks better on paper but people complain about the right direction when they need it.

The x-serie can have that problem if the setup is not good.

Edited April 26, 2006 by dusee

[+La Perouse]

While watching my favorite lawyer show on TV tonight I let my 60cx track for 1 hour in 10 second intervals. This was in a 2 story house with the weather outside overcast and pretty humid. I had solid bars on about 8 sats with no bar showing more than 50% and 3 or 4 showing about 20% in height. Stated accuracy during the hour was about 22'. I did not have an external antenna connected.

 

After it gathered about 300 points, I downloaded the UTM track coordinates using USAPhotomaps then imported them into an Excel spread sheet.

 

The chart below shows the ranked distance between the points and the averaged coordinate. As you can see, the great majority of the points were within 5 meters of the average.

 

I calculated the Standard Deviation (~4.0 meters) and threw out all points more than this above the average (~5.75 meters). By throwing out all these most anomalous points, the recalculated average coordinate was 1 meter away for the overall average! The actual accuracy of the weighted average coordinate seems to be about 4 meters west of where it should be. Oh yeah, the furtherest point was 25 meters away from the average.

 

To me, this is a testament to the high quality of the Garmin 'x' series! This also indicates to me that the simple average is just about as good as a weighted average.

 

[+La Perouse]

While watching my favorite lawyer show on TV tonight I let my 60cx track for 1 hour in 10 second intervals. This was in a 2 story house with the weather outside overcast and pretty humid. I had solid bars on about 8 sats with no bar showing more than 50% and 3 or 4 showing about 20% in height. Stated accuracy during the hour was about 22'. I did not have an external antenna connected.

 

After it gathered about 300 points, I downloaded the UTM track coordinates using USAPhotomaps then imported them into an Excel spread sheet.

 

The chart below shows the ranked distance between the points and the averaged coordinate. As you can see, the great majority of the points were within 5 meters of the average.

 

I calculated the Standard Deviation (~4.0 meters) and threw out all points more than this above the average (~5.75 meters). By throwing out all these most anomalous points, the recalculated average coordinate was 1 meter away for the overall average! The actual accuracy of the weighted average coordinate seems to be about 4 meters west of where it should be. Oh yeah, the furtherest point was 25 meters away from the average.

 

To me, this is a testament to the high quality of the Garmin 'x' series! This also indicates to me that the simple average is just about as good as a weighted average.

 

Did you consider taking the mode as well as than the mean? I say that as my experience has been that the mode gives a more replicable result. Anyway, nice to know Sirf III is as good as it is hyped up to be.

 

[+clan MacLeod]

was the unit standing up or did you have it laying on its back? I've read that this will make a bit of difference. Just curious.

It is nice to know what the GPSr will do before you have to use it in an area that is unfamilliare.

[+IVxIV]

I've always been able to acquire a signal lock while indoors with my several-year-old Lowrance iFinder Pro. It's nice to see Garmin is catching up

[planewood]

was the unit standing up or did you have it laying on its back? I've read that this will make a bit of difference. Just curious.

It is nice to know what the GPSr will do before you have to use it in an area that is unfamilliare.

 

Standing up. I'm tracking now with it outside with an antenna.

[planewood]

This time I let it track for 4 hrs outside under a clear sky with an external antenna.

 

The averaged coordinate seems to be plotting about 2' north of the actual location.

 

Edited April 27, 2006 by planewood

[+rdb3141]

your analyses are correct on paper

 

but it is a bit strange to use a gps at home were you now every inch.

And what do you want to prove?

 

The sirf III application is ment for finding your way in extreme difficult conditions.

Drift and reception don't mean a thing; does it point in the right direction when you need it.

There is also a comparison with the Explorist 600 which looks better on paper but people complain about the right direction when they need it.

The x-serie can have that problem if the setup is not good.

 

I don't understand most of your post. Inside your home is a rather difficult condition. Yes, testing under tree cover, in a canyon, et cetera would be useful too, but I don't understand the hostility.

 

"Pointing in the right direction" is more for a compass than a GPS. Drift and reception don't mean a thing??

 

Thanks, planewood, for your efforts. I'm very happy with my 60csx save the WAAS problem.