GPS How does it measure distance?

[845's]

Does GPS go from pt to pt via a LEVEL straight line or with uphill/downhill calculations. Thanks.

[thruzek]

It measures distance from point to point.

 

T

[limpwrist]

Any device that compensates for slope (elevation changes) when calculating distance as some of the laser rangefinders are capable of doing, is not allowed by USGA and R&A.

[hoganfan924]

Any device that compensates for slope (elevation changes) when calculating distance as some of the laser rangefinders are capable of doing, is not allowed by USGA and R&A.

 

GPS does take elevation into account as it measures point to point distance including the effect of topography. This is the same as what a (legal) laser rangefinder will do. What the illegal laser rangefinders do (laser with slope compensation) is calculate an equivalent level distance. For example, if the straight line point to point lasered distance is 150 yds. but the hole is 10 yards below your level, the rangefinder will read a number less than 150 when slope compensation is activated (let's say 143) and therefore (assuming no wind) a 143 yard shot is called for (don't know the actual algorithm, just an example)

[limpwrist]

Any device that compensates for slope (elevation changes) when calculating distance as some of the laser rangefinders are capable of doing, is not allowed by USGA and R&A.

 

GPS does take elevation into account as it measures point to point distance including the effect of topography. This is the same as what a (legal) laser rangefinder will do. What the illegal laser rangefinders do (laser with slope compensation) is calculate an equivalent level distance. For example, if the straight line point to point lasered distance is 150 yds. but the hole is 10 yards below your level, the rangefinder will read a number less than 150 when slope compensation is activated (let's say 143) and therefore (assuming no wind) a 143 yard shot is called for (don't know the actual algorithm, just an example)

 

Is that not the same thing I just said? I didn't say GPS is not capable of determining changes in elevation, just that it would violate the USGA/R&A ruling if the device were to compensate for those changes when calculating distance.

[stevesxm]

with all due respect i don't think you are correct about the gps. if you zero your gps and then move 1 yard forward off a cliff and go 200 yards straight down, your gps is going to read 1 yard. if you use your laser and aim it down that same cliff face, it will measure the hypotenuse of that 1 x 200 triangle . in the great scheme of things the diffences are inside the percentage of error of the ability of any of these things to read. think about it... if you are 100 yards out on a slightly up hill fairway are you saying to yourself " gee this fairway is uphill at a 3 deg angle therefore the TRUE distance is really .998629 x the actual measured distance " ? no... i don't think so. if your tee shot lands on the top of the hill at the hundred yard marker and the green is 50 feet below .... do you say... " gee thats only an effective 98.6 yard ball flight i better not hit that 50 deg wedge after all..."

 

no... these things in their most basic sense are 100 times better at getting the distances right then anyone that is using them has the ability to hit . they are a good guide to basic club selection but anything outide of military gps doesn't have anything like the accuracy that some of you and ALL of the manufacturers are giving them credit for.

[limpwrist]

GPS will also measure that distance along the hypotenuse based on the change in elevation detected by the satellite.

[845's]

What is the standard way a GPS gives measurements- LEVEL yardage or hypotenuse reading/straight to flag. Thanks.

[PingG10]

The standard reading for a GPS is straigth line distance ("as the crow flies"). GPS is capable of calculating altitude (if the appropriate number of satellites are available and the unit is designed to do so)-this would indicate that slope (or hypotenuse) distance calculation is theoretically possible-provided that the mapped point you are measuring to was mapped with an altitude variable and the slope corrected distance calculation capability is built into the computation algorithm.

 

I suspect that most golf GPS' use only 3 variables in triangulation of distance from the known point and therefore do not calculate an altitude component (my GPSCaddie certainly doesn't). I also know that when I map points on my GPSCaddie it does not map an altitude component so no triangulation would be possible. My boat GPS, on the other hand, is capable of measuring altitude (not very useful in a boat) but the unit is designed to be used in either boats or aircraft.

[stevesxm]

level. there is no slope or terrain compensation in any gps be it marine, automotive, military or hobby that can compensate for elevation change. the satellite has no idea at all how high or low relative to sea level the reciever is. within the military equipment where they have the terrain elevations already mapped into the software as a matter of record in a look up table, the accuracy is much better. but that is a device SOFTWARE function... i.e it KNOWS 18 .25 .46 N x 63.37.35 W is at 2230 ft elevation because some one TOLD it that when the software was written. consequently the math it does is based on multiplaner geometry not mono plane geometry. the laser stuff uses a doppler radar which doesn't know anything about elevation either UNLESS they have built an inclinometer into them which would be straight forward enough. THEN it has the angle data nec to do an accurate calculation for distance.

 

but my point remains... all this " angels on the head of a pin" resolution is really nonsense for the most part. a typical green is what... 2500 sq ft more or less ? how many people do you play with if you put 10 balls on the ground at a KNOWN 150 yds and then hit that 60 ft circle 5 out of 10 times ?

 

how about 2 out of 10 ? since we are not playing golf on the slopes of the andes, the percentage error due to angle or elevation is less than a couple of % worst case. who cares ? until the resolution of your shot making can get within an order of magnitude of that, all of these devices are plenty good enough for what they should be used for which is to keep you from being wrong by 20 yards. you don't need a color screen with aerial views to do that.

[arkstorm]

the laser stuff uses a doppler radar which doesn't know anything about elevation either

 

Umm...no it doesn't. The laser uses a laser, not a radio (radar) signal!

 

And the GPS uses a straight line method for determining distance. The reading it gives you is as the crow flies. I.e., if there was a mountain between you and the hole the GPS would tell you a distance to the hole as if there was a tunnel through the mountain directly to the hole.

 

The theoretical problem with moving one yard forward but down a 1000 foot cliff is actually a problem for GPS but doesn't come up so much in golf.

 

As for golf GPS requiring military GPS precision to be helpful, that's not right either. Civilian GPS is enabled to +/- 3 feet and even tour pros can handle that variance.

[PingG10]

As a further point of clarification I would add that GPS receivers calculate X,Y,Z and T based on data from the satellite constellation-Z being an altitude component. The altitude component is receiver location relative to the radial distance from the center of the earth to the orbit of the satellites (see http://en.wikipedia.org/wiki/Global_Positi...ting_positions).

 

The issue is knowing a base to relate the receiver position to-for boat GPS this is easy, sea level is zero-for aircraft it is a bit more difficult-generally requiring a look up table of previously altitude mapped coordinates-as I mentioned in my prior post, my golf GPS unit does not map an altitude component (not because it is not capable of but because the software apparently discards the z component-at least I cannot see it in the data files). Therefore it cannot set an altitude base reference between two points of known altitude and thus cannot calculate a slope corrected distance (based on the delta z distance)-my boat GPS can do this as it can be used in an aircraft (with additional data provided on known points). GPS is an acceptable means of aircraft precision navigation (both commercial and private) so obviously altitude is an important measurement capability.

[arkstorm]

Its important to note one more thing about GPS and laser range finders alike:

 

Regardless of which one you use they are a lot more helpful than finding distances on fairway plates and sprinkler heads. They speed up play and help you shoot lower scores. They're not perfect. Each has its advantages over the other. And neither are a tour caddy. But they are a good thing for the game.

[Gsco]

with all due respect i don't think you are correct about the gps. if you zero your gps and then move 1 yard forward off a cliff and go 200 yards straight down, your gps is going to read 1 yard.

 

 

No, it's going to read 200 yards. You will be 200 yards away from your last point.

 

Actually, 201 yards.

[rkruff]

Wrong....It will read 1 yard

[Gsco]

Wrong....It will read 1 yard

 

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

[rkruff]

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.

[Golfdog]

This is like listening to 10-year old boys argue about something. :lol:

[Gsco]

Well, my Dad's better than your Dad.

[rkruff]

Well, my Dad's better than your Dad.

 

My dad is dead.

[Golfdog]

Well, my Dad's better than your Dad.

 

My dad is dead.

 

I think he was making a joke, trying to lighten the mood.

[rkruff]

Well, my Dad's better than your Dad.

 

My dad is dead.

 

I think he was making a joke, trying to lighten the mood.

 

I know....Not a problem. Just fooling around. Would still like the answer about the 1 yard forward and 200 yards down scenario. The Laser would read the square root of 401 (200*200) + (1*1) and the GPS would read 1 yard. Am I missing something?

[Gsco]

Well, my Dad's better than your Dad.

 

My dad is dead.

 

Did he get hit by a Hypotenuse?

 

We did this last week arguing.. We were on a balcony, set the mark, walked down right underneath and it read 20 yards. Came back up and it read 0 to 2 yards. Is this what we are talking about?

 

 

Oh, and I read he was kidding. I'm not an animal!

[limpwrist]

square root of 401

 

40,001

[rkruff]

square root of 401

 

40,001

 

Wrong....20 squared equals 400....1 squared equals 1.....sum is 401 and the hypotenuse is equal to the square root of that.

[limpwrist]

This is what you had in your previous post:

 

The Laser would read the square root of 401 (200*200) + (1*1)

 

The scenario given earlier was 1 yard forward and 200 yards down a cliffside. 200*200=40,000 You are correct in that 1*1 does indeed equal 1, so the hypotenuse would equal the square root of 40,001, which is still 200 yards rounded to the nearest tenth. Twenty was never part of the equation.

[rkruff]

This is what you had in your previous post:

 

The Laser would read the square root of 401 (200*200) + (1*1)

 

The scenario given earlier was 1 yard forward and 200 yards down a cliffside. 200*200=40,000 You are correct in that 1*1 does indeed equal 1, so the hypotenuse would equal the square root of 40,001, which is still 200 yards rounded to the nearest tenth. Twenty was never part of the equation.

 

You are correct....I was somehow thinking 20 instead of 200. Square root of 40,001 is the length of that hypotenuse.

[larrybud]

Does GPS go from pt to pt via a LEVEL straight line or with uphill/downhill calculations. Thanks.

It depends on the GPS device. GPS devices track satellites. You need a minimum of 4 satellites to measure in 3-D. You need 5 to measure time. I haven't looked at the specs on golf GPS devices to know how many those use. And the accuracy depends on the relative position of the satellites to one another. But the tolerance in 4 satellite GPS receivers is not very good (about 50 feet). Real accurate GPS devices like for land surveys use 8+ satellites.

 

Older GPS devices used a solid state barometric pressure sensor to indicate approximate height.

[Play10s]

So, this question was lurking in the back of my head and I HAD to get the answer.

 

So, here goes. We all know that for a GOLF GPS to be legal, it would only take the Lat & Log coordinates and ignore any altitude. Most, if not ALL Golf GPS systems use this same idea. Although the GPS signal includes altitude info, the units ignore that piece of info when calculating distances.

 

So when you are at a location the distance you are receiving is not the hypotenuse of the triangle, it is the flat line (base) of the triangle as you would see on a map.

 

Does GPS go from pt to pt via a LEVEL straight line or with uphill/downhill calculations. Thanks.

[OrangeBlood]

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