GPS Accuracy Experiment

[DaveLeeNC]

I did this experiment over a year ago and posted the results on another board. I thought I'd post this here as well. It was done using an iGolf Caddie.

 

At the time I didn't have a way to measure absolute distances easily. So what I did was to take a couple of arbitrary points in the range of 100-200 yards, and just do repeated measurements of these same points a whole bunch of times over an extended period of time. I used the repeatability of these measurements as kind of a proxy for accuracy. Absolute accuracy certainly can't be any better than this.

 

The details are that I mapped four points that are 100 to 200 yards from my house (surrounding my house). Then I measured these four distances (from a fixed position in my front yard) 70 times over a 5 day period (280 measurements). Here is what I found.

 

 

91% of the measurements were within 3 yards of "correct" (where "correct" is

the average of all the measurements for that point)

 

97% within 4 yards

 

99% within 5 yards

 

This pretty much matches my experience on the course.

 

I ultimately became a laser guy simply because the only information that I wanted on a regular basis that wasn't already available from sprinkler head info (in most cases) is accurate distances to the pin on shots inside 100 yards.

 

dave

[phil75070]

What GPS did you use? Not all golf GPS's are created equal. For example, they differ in the number of "channels" or satellites they can acquire and some are WAAS enabled. The actual measured accuracy of the WAAS system, based on the NSTB's findings, is .9 to 1.3m. Without WAAS, the measured accuracy ranges from 2.5 to 4.7m, which seems to coincide with your experiment.

 

Advertised accuracy for Bushnell lasers is +/- 1 yard. Don't know why everybody says a laser rangefinder is "exact".

[DaveLeeNC]

As stated in the post the device was the iGolf Caddie (older/original model). The measurements were done with WAAS on and Stabilizer Off (my experience was that this mode provided more consistent dresults).

 

According to the Garmin site, WAAS enables accuracy to 3 meters 95% of the time (similar to my results). http://www8.garmin.com/aboutGPS/waas.html

 

dave

[blkdiamond]

Please don't take offense to this, but are you actually able to hit your ball within 5 yards 99% of the time, 4 yards 97% of the time and within 3 yards 91% of the time?

[atlanta golfer]

I use both gps skycaddie and a rangefinder. The reason to use one over the other has nothing to do with accuracy. When you are measuring distance to clear a hazard or front and back of green, plus or minus a few yards is fine.

 

Personally, if I had to choose one over the other, I would choose rangefinder, not becasue it is more accurate but because it gives you distance to the pin. It also gives you distance to anything else you are interested in such as the tree at the end of the fairway. The rangefinder is also simpler, lower tech, has longer lasting batteries, etc.

 

Again imho both are useful. Either one is nice to have. If I could only have one I would go rangefinder.

[DaveLeeNC]

Please don't take offense to this, but are you actually able to hit your ball within 5 yards 99% of the time, 4 yards 97% of the time and within 3 yards 91% of the time?

 

I changed to a laser because it measures distance to the pin, rather than distances to the front/center/rear. It had little to do with the absolute accuracy of GPS device itself. I would probably stayed with the iGolf device if it measured distances to the day's actual pin placement.

 

I honestly don't know how accurately I can determine the distance to the pin when I am 50 yards from the center of the green (known from my GPS), 20 yards left of a center in the rough(estimate), 68 yards from the rear of the green (known from my GPS), and the pin looks like it is maybe 6 paces from left side and 8 paces (10 paces maybe??) from the rear (as viewed from 50 yards away).

 

I don't have a clue as to the accuracy of whatever yardage I decide it is using God knows what mental geometric process. But in this case 5 yards matters (to me). 3 yards - probably not.

 

dave

[v205]

How accurate are professional caddies? Are they more accurate with their book measurement compared to a GPS or Laser?

 

On a side note, the GPS should allow a good player to really improve their GIR stats. If that stat is at pro level, then maybe get a Laser to try to shoot closer to the pin.

[DaveLeeNC]

How accurate are professional caddies? Are they more accurate with their book measurement compared to a GPS or Laser?

 

On a side note, the GPS should allow a good player to really improve their GIR stats. If that stat is at pro level, then maybe get a Laser to try to shoot closer to the pin.

 

Even though I am a laser guy, I actually have a slight preference for GPS when 150+ yards from the green. In this case accurate knowledge to the front/center/rear is more useful than precise yardage to the pin.

 

But for me laser wins out because accurate yardages TO THE PIN inside 100 yards is most critical/useful.

 

dave

 

ps. A Hogan story that I heard years ago. Hogan had a local caddie (the norm back then) and his caddie gave him the yardage 176, maybe 177 yards. Hogan stared at him for a good 10 seconds and finally said "well, which one is it?" I'd be surprised if the yardages from various point on the fairways provided by the caddies are as good as 3 yards. Just my opinion.

[atlanta golfer]

How accurate are professional caddies? Are they more accurate with their book measurement compared to a GPS or Laser?

 

On a side note, the GPS should allow a good player to really improve their GIR stats. If that stat is at pro level, then maybe get a Laser to try to shoot closer to the pin.

 

Having both a gps skycaddie and a rangefinder, I really disagree with this. Many modern greens are 20 to 30 yards wide and/or the same amount deep which is 2 or 3 clubs distance difference. I would much rather have the pin position and then select a club, then simply know front and back of green. I agree that as a 13 handicapper I have a big margin for error. But I would rather work my plus or minus error shots in to a fixed and known exact yardage (pin) then simply aim for the center of the green.

 

btw I agree with the post above, if I am 5 iron or greater from the green then I am going for the green and the front and back are good for me. But when I get within, say, 7 iron or better distance, I want to know exact yardage to the pin.

[rliujr]

Being a high handicapper at the moment, I am perfectly happy with my SG5 since I'm not in the fairway as much as I would like to be. Knowing the various distances of hazards is more important to me then knowing the exact yardage to the pin. Having the 3 yardages on the green, i.e. front/mid/back, and the flag location is more then adequate for me at this time. Maybe when I become a single digit handicapper will I need a more exact range to the pin. But for now, I love my SG5. :yes:

[phil75070]

How accurate are professional caddies? Are they more accurate with their book measurement compared to a GPS or Laser?

 

On a side note, the GPS should allow a good player to really improve their GIR stats. If that stat is at pro level, then maybe get a Laser to try to shoot closer to the pin.

 

Having both a gps skycaddie and a rangefinder, I really disagree with this. Many modern greens are 20 to 30 yards wide and/or the same amount deep which is 2 or 3 clubs distance difference. I would much rather have the pin position and then select a club, then simply know front and back of green. I agree that as a 13 handicapper I have a big margin for error. But I would rather work my plus or minus error shots in to a fixed and known exact yardage (pin) then simply aim for the center of the green.

 

btw I agree with the post above, if I am 5 iron or greater from the green then I am going for the green and the front and back are good for me. But when I get within, say, 7 iron or better distance, I want to know exact yardage to the pin.

 

With a SkyCaddie (or Golf Guru) and a pin sheet, you can get a pretty close approximation of the distance to the pin with their Intelligreen (and Green Zense) features. You then have the ADDED advantage of knowing just how much room you have in front or behind the pin to know where to plan your miss. And you get it all very quickly, practically at a glance.

[atlanta golfer]

How accurate are professional caddies? Are they more accurate with their book measurement compared to a GPS or Laser?

 

On a side note, the GPS should allow a good player to really improve their GIR stats. If that stat is at pro level, then maybe get a Laser to try to shoot closer to the pin.

 

Having both a gps skycaddie and a rangefinder, I really disagree with this. Many modern greens are 20 to 30 yards wide and/or the same amount deep which is 2 or 3 clubs distance difference. I would much rather have the pin position and then select a club, then simply know front and back of green. I agree that as a 13 handicapper I have a big margin for error. But I would rather work my plus or minus error shots in to a fixed and known exact yardage (pin) then simply aim for the center of the green.

 

btw I agree with the post above, if I am 5 iron or greater from the green then I am going for the green and the front and back are good for me. But when I get within, say, 7 iron or better distance, I want to know exact yardage to the pin.

 

With a SkyCaddie (or Golf Guru) and a pin sheet, you can get a pretty close approximation of the distance to the pin with their Intelligreen (and Green Zense) features. You then have the ADDED advantage of knowing just how much room you have in front or behind the pin to know where to plan your miss. And you get it all very quickly, practically at a glance.

 

I agree with you but I play a lot of different courses and most of them do not have what I would call a pin sheet. The most typical situation is 3 different colors for front middle and back. Personally, I've been typically using only my rangefinder when I have a good view of the green or a good view of the fairway from the tee. When the tee shot is blind or the green is elevated, then using the skycaddie is a big advantage. When needed, I can still look at both in total time of less than 30 seconds while others are still wandering around looking for a sprinkler head. I actually don't think anyone can go wrong with either device. Either one is a nice advantage.

[reeves_]

Have you done a similar experiment with a laser rangefinder?

[v205]

Just got a Scout 1000 (very compact size), very accurate (+/- 1m) from my prelimary testing around home to points (power poles / trees) ranging between 5m-100m. When I get a chance, I'll try to see if i can pickup a flag from 250m (Tour V2 was claiming 300 yards to flag, more likely a standing flag!) and 200m to see how easy/hard it is to do it. Althought realistically for me, distances more than 150m is more for ranging to non-pin targets (bunkers, hazards, OB etc).

 

Have you done a similar experiment with a laser rangefinder?

[v205]

No problem hitting flags from 200m. Anything further will need a few tries.

 

The flags were dropped due to still wind day.

[XC967]

How do you test accuracy of a range finder at home? Are you just testing how accurate you can repeat a task or do yo have a spot with a actual measured distance? If so how was that distance measured?

[stevesxm]

i took the basic sonocaddie out to the local course here that they had no map for. i used a measuring wheel to walk off a variety oft distances and checked those numbers against what old sono said. and they were inside a couple yards every time and spot on repeatable. i mapped my course using the front edge of the green as my reference and then identified all manner of hard landmarks and repeatable positions and created a course notebook hard copy with all the distances. now when i play for fun i use my notebook ( legal for tournament play ) for my first estimate and then just have a glance at the gps for confirmation. the " shot distance" feature made it a snap to profile my clubs for distance and i use that to keep track of distances vs winds. that info paid huge dividends in that last tournament which was horrible conditions with VERY high winds... which i had practiced in a week before and had data on. won by two strokes gross and four net.

[DaveLeeNC]

i took the basic sonocaddie out to the local course here that they had no map for. i used a measuring wheel to walk off a variety oft distances and checked those numbers against what old sono said. and they were inside a couple yards every time and spot on repeatable. i mapped my course using the front edge of the green as my reference and then identified all manner of hard landmarks and repeatable positions and created a course notebook hard copy with all the distances. now when i play for fun i use my notebook ( legal for tournament play ) for my first estimate and then just have a glance at the gps for confirmation. the " shot distance" feature made it a snap to profile my clubs for distance and i use that to keep track of distances vs winds. that info paid huge dividends in that last tournament which was horrible conditions with VERY high winds... which i had practiced in a week before and had data on. won by two strokes gross and four net.

 

One thing that I observed about measurement repeatability is that readings are very consistent over a period of a minute or two. But over a time period of hours or days is where "the real variability" shows up. And as I said - while the accuracy was not a good as you might wish for, the ultimate issue for me was not measurement accuracy.

 

dave

[stevesxm]

well... can't speak for yours.. but when i play for fun i carry my notes and the sonocaddie and the same tree that was at 172 last week is at between 170 and 174 this week. thats good enough for me

[firegolfer]

The only problem I have with the laser (I have both laser and gps) is that while it tells you that your exact pin yardage is 138 yards, you may not be able to hit the front of the green with the laser and find out that it is 130 yards. Now you don't know that you can only be 8 yards short or no luck. With the gps, the trade off of course is guessing where the pin is in relation to the front back or center. But at least you know for certain your minimum or maximum carry distance. I would have to think that for the average golfer (like me) that this is way more important than knowing exactly where the pin is, but not how far or short I can hit it. (I can't get the ball to stop and back up 8 feet just yet.) I mean sure, if I could hit the ball to an exact distance everytime, then the only number I would need is the pin, but hey, if I could do that I probably wouldn't be typing on this board right now, I'd be finishing up my round in florida!