GPS How does it measure distance?

[stevesxm]

Wrong....It will read 1 yard

 

Then go do it. I did. You're wrong.

 

 

Go take a Geometry class. It will read 1 yard.....Base of the triangle with GPS.....Hypotenuse for Laser.

 

i did... just for the sake of this discussion. i stood on the 15 th floor of a hotel today and zeroed the display. took the elevator down to the street and stood under the balcony and the display said ( surprise ) ZERO.

 

you need to think in terms of the relative height of the satellite vs any height difference on the surface of the earth... you are talking about a percentage difference of the maximum deltas of a HUNDRETH of a percent... and even if your gps has a barometer, it better have a mechanisim for setting the base line to known local zero to be accurate.... which none of these have ... because the resolution would be so coarse as to make the result meaningless.

[DanZ]

So lefts say you are on an elevated tee that is 40 yards above the green which is 200 yards away. Which piece of information is more useful?

 

- 200 yards - What your standard golf gps will give you.

- 204 yards - What your standard rangefinger will tell you.

 

It's gotta be a pretty big height differential to make that worthwhile of a difference.

[larrybud]

Found this on a site....

 

 

 

GPS receivers have an in-built, idealised, model of the earth's surface and they generally measure their elevation from that. This model is called a geoid and may be, or may be not, close to mean sea level which is probably where what maps and other elevation definitions use. So if you want to use your receiver to check your elevation against a map, ensure you baseline your receiver's elevation display against the map to see what the difference is. This won't be consistent over a very large area, say 100km+, as the distance between the geoid and mean sea level does vary. Mean sea level itself does vary from place to place too.

 

The other point to consider is that GPS is designed for horizontal, not vertical accuracy. The vertical error is likely to be 1.5 time that of the horizontal EPE. There are some GPS receivers have built-in barometric altimeters, which function like those fitted to aircraft. The altitude/elevation that these units display will vary according to the pressure setting, and the reading may or may not agree with any conventional GPS receiver

Your info is old. I don't believe they make GPS receivers that have barometric altimeters in them anymore.

[stevesxm]

So lefts say you are on an elevated tee that is 40 yards above the green which is 200 yards away. Which piece of information is more useful?

 

- 200 yards - What your standard golf gps will give you.

- 204 yards - What your standard rangefinger will tell you.

 

It's gotta be a pretty big height differential to make that worthwhile of a difference.

 

thats VERY good question and a very interesting illustration... first, my answer would be ( as it has been all along) " who gives a sh*t ? " no one you or i know or have ever seen EVER can hit repeatably inside a 12 foot ccirle at 200 yards or even at 20 yards for most of us...

 

second if you believed your gps and clubbed for 200 instead of 204 ( i just KNOW you carry 36 clubs that are distanced 4 yards apart) your strike would cross the lateral plane of the trajectory at 200 as planned ( BOY youre good) but then instead of hitting the ground and stopping it would continue to drop that 120 feet of elevation you started at and ( surpise again) continue in the same balistic arc you started with, which would carry it , by my rough calculations, about another 35 feet.so you would be about 15 feet long. if you clubbed for 204 like your laser said, you would be longer still because all your club selection distances are predicated on a horizontal plane where the start and finish are on the same level.

 

remember my first example ? the ball on the edge of the cliff ? move a yard and go straight down ? " well my gps would say 1 yard and i would club for that and miss long by the elevation trajectory error or about 20 yards . your laser would say 201 and you would miss by roughly as long as you can hit your 5 wood plus the elevation change delta or about 350 yards.

 

since, as has been observed we aren't playing on the slopes of everest, i would suggest that the gps is a better deal across the board all the time.