Which GPS is the most accurate?

[x100]

Just wondering which gps units offer the best reception, which I'd assume would be the most accurate. I had a sg3 and wasn't very happy with it. My friend just got the sg5 and that seems much better. Are there other companies that are better and offer the amount of courses that skycaddie has. Like Igolf, sonocaddie or sureshot. To me accuracy and reliabilty is more important than features.

[Solutions Etcetera]

I think the only vendor with a course base as mature as Skycaddy's is GolfLogix. It is pricey and not as feature laden as many others but the hardware is bullet proof (basically a Garmin ETrex).

[PingG10]

Basic accuracy of GPS units should be all the same provided they can lock in on 4 satellite signals (4 signals are necessary to determine the 4 variables (x, y, z and time, 3 if altitude is taken out of the equation) that are then converted into more user friendly information such as latitude and longitude). The more important question is how well can the receiver lock on to the minimum of 4 (or 3 in the case of altitude not being calculated). There have been numerous posts regarding certain SG models not maintaining lock. I've the iGolf sky caddie II model and can verify that I've never lost lock under any conditions I've experienced thus far.

[x100]

Does the skycaddies have the most courses?

[PingG10]

SkyCaddie claims the most courses. iGolf has a significant database of courses-I've only had one course that I wanted that wasn't available. There has been some discussion regarding the relative accuracy of "walked" courses (SkyCaddies approach) versus "mapped" courses (most other vendors use satellite or other imagery to map features). There is some truth, mathematically, to the argument that a "walked" course is more accurate than a "mapped" course (if all other variables, such as human error are held constant) however my experience thus far has been that any difference has been negligable.

I'd also note that mapping a course is very easy with the the iGolf unit-I mapped the course that wasn't available (Chambers Bay Tacoma WA.-brand new, links course) yesterday. I estimate that it might have added 1 or 2 minutes to each hole. I only mapped F/C/B of each hole-I didn't feel that it made sense to add custom layups or other features the first time I played the course.

[Psycho77]

From that topic:

[url="http://www.golfwrx.com/forums/index.php?showtopic=126150&st=80&start=80"]http://www.golfwrx.com/forums/index.php?sh...80&start=80[/url]

It seem that peoples really love the GPS Golf Guru for accuracy and the signal doesnt cut.

Good reading

[Solutions Etcetera]

[quote name='gdoakes' post='876391' date='Jan 22 2008, 07:29 AM']There is some truth, mathematically, to the argument that a "walked" course is more accurate than a "mapped" course (if all other variables, such as human error are held constant) however my experience thus far has been that any difference has been negligable.[/quote]
Could you go into more detail regarding this? Since a handheld has an accuracy of +/- 3 meters, and satellite images a resolution as high as .6 meters, how is it that a walked course mapping would be inherently more accurate?

[PingG10]

View it as this-the GPS receiver on the walker "knows" where it is due to the triangulation from the 3 (or 4)GPS satellites that it is using. Relative accuracy-wise any GPS receiver returning to the same point should obtain the maximum accuracy possible with GPS (holding all other variables in dither, jitter, etc. constant). A "mapped" course inputs the x,y and possible z coordinates thus when a GPS receiver goes to these "derived" points there is a potential inaccuracy introduced by a GPS receiver never having "been" there before. This can be exacerbated when algorithms that convert the GPS coordinates to something more usable for information and display do what they do.

The noted accuracy of the imagery significantly reduces the potential for mapping errors-the error I was speaking of is more of a mathematical accuracy between real GPS coordinates (those obtained by having a GPS receiver locate the coordinates from 3 or 4 satellites) and "synthetic" GPS coordinates (those obtained by synthesizing the coordinates from other sources than the NAVSTAR constellation) . As I said this should be (all other variables held constant) negligable. The "repeat accuracy" and "synthetic accuracy" of GPS was one of the great improvements for navigation relative to LORAN.

[Solutions Etcetera]

Hmmm... Are you saying that the error offset from a GPS signal at a given x,y,z coordinate would always be the same. My understanding is that it would always be a random offset.

[msguillory]

I am wondering the same thing. It would seem to me that each device might be just slightly different, so either way it is mapped the readings could be off. The only way to have the most accurate readings would be a good GPS receiver that is consistent with it's corrdinates and have that device map the points, so user mapping would seem to be the most accurate.

With all that being said, personally I think that right now either way of mapping is probably close enough. I have read several reviews on here where people have had more than one device (say SkyCaddie and iGolf) and have nearly the same readings. Outside of a PGA player, if it says 175 to the center of the green and it is actually 177, I don't see how that is going to effect my game, or most anyone elses.

It seems to me that the most important aspect of these Golf GPS devices is that they has a good strong signal and give accurate, CONSISTENT readings everytime. I have heard of some that might show different reading while you are standing still, that is no good. Whenever I am at one particular point on a course I want it to give the same reading everytime I play.

I am still looking at GPS Golf Guru, and SkyCaddie SG2.5. I don't care about screen above or below, but I do like both of these for their true shape greens with angle of attack perpective. I think that most of the other ones out there are worthy as well, except there have been a lot of poor reviews of SG3/4, I think because of their reception was not as good as the newer ones (or even the SG2).

[PingG10]

What I'm saying is GPS is more potential more accurate returning to a point where a GPS has been than it is going to a point that one has never been before. Really this should be regardless of the receiving unit (within reason) as the mathematics of solving the triangulation equation is the same.

Regarding the above post, I would strongly recommend the iGolf GPS Caddie II unit, if those are your most important selection criteria. My unit works very accurately in motion or stopped (except when registering a user defined mapping point-when the unit must remain still for about 4 seconds to plot the point). I'm not generally concerned about the green perspectiive-I've seen the feature on one of my buddies SkyCaddie and don't think it adds all that much to my perspective on the distance to the flag. I personally think that the number and ease of user defined points as well as not having the data lapse due to a subscription lapse are the most significant differentiators.

[Solutions Etcetera]

[quote name='msguillory' post='876783' date='Jan 22 2008, 11:50 AM']It seems to me that the most important aspect of these Golf GPS devices is that they has a good strong signal and give accurate, CONSISTENT readings everytime. I have heard of some that might show different reading while you are standing still, that is no good. Whenever I am at one particular point on a course I want it to give the same reading everytime I play.[/quote]
It won't. That is the point I was trying to make. The error offset in the GPS is random. Given perfect reception, and being at point X, at any given time the offset will be different (within about +/- 3 yards) in any direction.

GPS signals are time based, and even with WAAS based correction, position accuracy will vary based on many factors including conditions in the ionosphere, possible causes of multipath distortion (reflections), and the current status of the GPS constellation.

Your fear of the unit that is constantly updating is IMHO unwarranted. More accurate receivers with faster sampling will do this. You will see differences when under the roof of your cart versus a clear sky view. This is a GOOD thing. If a receiver was not showing me variances based on outside disturbances I would suspect it is using some form of variance averaging voodoo in it's firmware. I would prefer to see the variances myself as they occur.