Cloudy Days

[planewood]

Been playing with my 60 cx.

 

The attached image is of my cul-d-sac in front of the house. The center is a surveyed location and I'm using those coordinates as truth. The Google image, by the way, perfectly matched those coordinates. This is one of their high definition surburban images. The cul-d-sac is 75 feet across.

 

The points have been marked with 100 averages each over the last 4 days. With 15.2 the sky was cloudy and highly overcast but still pretty low humidity. With 16.2 the humidity was miserable we were socked in with heavy clouds. The other points were taken when it was low humidity and very clear. These last two points only had a medium lock on 5 or 6 satellites. With the others, 8 or 10 bars were maxed out. The distance from 16.2 to the center is 22'. 15.1 is 2.9' away from center.

 

Oh yeah, WAAS was turned off for all readings cause I can't get any reception from them here.

 

 

Anyone else doing this?

Edited March 17, 2006 by planewood

[GeoBobC]

My guess is that satellite configuration has more to do with change in accuracy than cloud cover.

[planewood]

My guess is that satellite configuration has more to do with change in accuracy than cloud cover.

 

You know, another nice feature to have when you mark a point would be an option to capture the satellite page to the data card in JPG format! And, give it the same name as the waypoint. Why not! We'll soon have 2 gig cards anyway.

 

In this location there always seems to be at least 4 or 5 satellites in, or touching, the inner circle. That's probably true anywhere though.

 

The displayed accuracy for those inner points was 8'-14'. For the two outer points it was 18'-22'.

[+Rosterman]

Was the time of day the same for each fix?

[Alphawolf]

Without a solid WAAS fix, this is entirely within expected accuracy norms for any civilian GPS receiver...

[planewood]

Was the time of day the same for each fix?

 

No, just depended on when I found one of those 'round-tuits'. Anywhere from 9am to 10pm.

 

Today I set tracking to 5 seconds and let it track for about 5 minutes. It wandered around from as little as 3' away to as much as 10' away. Kinda in a squirrely looking circle. There were no wild outliers.

 

Being new at this GPS stuff, I'm just totally blown away by the accuracy of this technology. Mindboggling! Can't wait till they get a WAAS up that I can lock onto.

[+TotemLake]

Was the time of day the same for each fix?

 

No, just depended on when I found one of those 'round-tuits'. Anywhere from 9am to 10pm.

 

Today I set tracking to 5 seconds and let it track for about 5 minutes. It wandered around from as little as 3' away to as much as 10' away. Kinda in a squirrely looking circle. There were no wild outliers.

 

Being new at this GPS stuff, I'm just totally blown away by the accuracy of this technology. Mindboggling! Can't wait till they get a WAAS up that I can lock onto.

 

The satellites are not stationary, so the geometric configuration is always changing thus, the caluculations will always come up with a slightly different answer. The fact you're within 30' at any given time is doing well. To gain less EPE is doing exceptionally well and requires many birds in the air with the majority of them being closer to the horizon rather than directly overhead. So, the wider the horizon with fewer obstacles in the way, the better your accuracy... dependent upon the fact you have the satellite configuration to take advantage of that clear horizon.

[planewood]

The satellites are not stationary, so the geometric configuration is always changing thus, the caluculations will always come up with a slightly different answer. The fact you're within 30' at any given time is doing well. To gain less EPE is doing exceptionally well and requires many birds in the air with the majority of them being closer to the horizon rather than directly overhead. So, the wider the horizon with fewer obstacles in the way, the better your accuracy... dependent upon the fact you have the satellite configuration to take advantage of that clear horizon.

 

Thanks TotemLake -

 

Never had heard that before about needing some satellites on the horizon, but it makes sense. I do remember that on those cloudy days that most of my locks were directly over head. Do you think that might explain why those points plotted futher away?

[+TotemLake]

Sorry for the late response...

 

Yes, the more satellites directly overhead and the fewer nearer the horizon, the less accurate the plots. You want a good spread of birds in order to get a good geometric triangulation.