Garmin 705 questions?

[daj]

Hello,

Just sat here pondering on how accurate the 705 actually is? Been running one since Christmas and never match anyone elses total miles and just noticed after loading some of my routes onto a mapping site the difference between what the Garmin said at the time and now the actual route offical is nearly 1000ft out over 40 miles :?

Was thinking along the lines of my auto wheel sizing being wrong but googling it I am runnning correct for 700 wheels.

Anyone else have similar goings on?

Cheers

Dave

 

[Iwasgoodonce]

Is this a device that utilises GPS to gain a elevation fix or some sort of pressure sensor?

 

[daj]

Its GPS Mark , which is why I cant understand why the miles would be inaccurate ?

 

[Iwasgoodonce]

I'm guessing what you have there is a GPS unit working from an autonomous signal. This means it is receiving 'raw' uncorrected gps data probably using L1 gps signal. This is quite a long wavelength signal so we are looking at a horizontal accuracy of around 10-15 metres depending on the quality of the antenna.
Due to the fact that all the sattelite vehicles are at the same altitude (around 26Km) the elevation is around one and a half times less accurate than the horizontal. As a percentage, what is your error against the total distance travelled?

Sorry about the crap grammar and spelling, but this is a very strong beer!

 

[daj]

About 2 miles it always seems to be short? But it must mean my average speeds and Max speed ?

I am guessing this is your thing Mark?

 

[Iwasgoodonce]

I have an RTK GPS system that will establish your position to +/- 10mm horizontally. It won't fit on your handlebars though! If your gizmo mixes GPS with a cycle computer type thing, the best way is to line the valve on the wheel up with a chalk mark on the ground. rotate the wheel one whole revolution in a straight line and make another mark. Measure the istance and enter that. The mathematics behind the GPS is sound although if your routes involve trees and other such obstructions, the GPS will suffer greatly.

 

[OrangeRetro]

The barometric altimeter in the 705 needs time to calibrate, mine often needs to be on for about five minutes before its acurate..

As for distance.. erm that shoudl be spot on?

The 705 has a strong reciever so trees are unlikely to effect it.

Where are you getting your figures from? Garmin connect?

The mapping site might be incorrect.. Its quite difficult to cator for all the gps devices out there and the site might not be tested for 705 TCX data? If it is garmin connect that you are using, your 705 might be faulty.

PM me.. my site is working now and you can test it against my mapping.