Kerry.

quote:Originally posted by Alan2:How do you it won't be as accurate? MY test and trippy's test showed a majority of accuracy readings under 12 feet in two different places. What tests have been done to show this kind of accuracy is not consistant in other areas? Alan Without hindsight you really won't know what the difference in accuracy will be. That's one of the reasons why the 95% accuracy figure is spec's the way it is and don't forget there's another unknown 5% . As for tests enough. It's actually really quite easy to show there is no consistency in accuracy in different areas. Just for the sake of this particular exercise the following is some random accuracy examples for 3 locations on October 7, 2002 (Doy 280). These figures are the accuracy in metres RMS for the 24 hours based on C/A L1. The receiver types are unimportant as it really doesn't matter. Kingston, Jamaca - 1.9m RMS Casey (Antartic) - 10.6m RMS Manama (Bahrain) - 23.4m RMS One can be assured that there's certainly no consistency between any of them and there certainly would be a greater "inconsistency" in the period by period (minute by minute) accuracy throughout the day at Manama compared to say Casey and to a much lesser extent Kingston. The dynamics of the system simply can't be expressed that accuracy will be such and such at all places at any time, it simply don't work like that, hence the way accuracy is defined. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The Longitude question took John Harrison almost all his life to solve the problem of time. This outlines Harrison's time pieces known as H1, H2, H3 & H4. There is also a H5 not mentioned here. http://www.rog.nmm.ac.uk/museum/harrison/h1.html Cheers, Kerry. I never get lost everybody keeps telling me where to go

Alan, I realize what your saying but running a handfull of receivers at the same point regardless of the time frame is not within the meaning of GPS accuracy. Just because there was some consistency and that's what it is consistency doesn't mean that if one was to take all those receivers somewhere else that the results would be the same. That's the thing with GPS and the specifications (including accuracy) it is a global system, the worlds first global utility and that's what the system has to cover (the entire world) including accuracy specs. That entire world also includes a few hundred km's into space. The system is currently running with all spares and things are fairly good but drop back to the design 24 and then loose any 1 or 2, which is a requirement (and possibility) of the specs then the world wide capability is on a minimum footing. There are several reasons why the system is consistently more accurate than figured but why manufacturers continually want to "massage" error circles (EPE's etc) is really a bit of a con. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Accuracy is a funny thing and limited single point in time positions really doesn't give an "overall" indication of the system or receiver accuracy, they are just that a single position in time. It could be dangerous (in some applications) to assume that GPS is such and such based on very limited data. Cheers, Kerry. I never get lost everybody keeps telling me where to go

There are "weather conditions" that can/could affect GPS reception but these are really not what we here on the ground might associate with weather. Most of the issues generally are in space with sunspots, geomagnetic storms etc. The system is an "all weather" system and severe weather shouldn't have any affects. I doubt you'd be worrying about if your GPS works if the weather ever got that bad/extreme to be a real issue. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Anders:Soooo, what's your "fair idea" then, if we come down to some good old numbers? 5°? 10°? I'm not aware of any hard-wired greater than 10 degrees and some are around 5 and then 0 degrees is fairly common (actually very common). For serious GPS observations the minimum is normally 15 degrees and even as high as 20 degrees for some applications but these receivers are configurable. Catch 22 with WAAS is the higher the mask cut-off the less chance of receiving these at low horizon latitudes. I'm not that sure if WAAS transmits corrections for all satellites in view (even if both base and roving receiever were seeing the same sats). With WAAS the base receievers have an elvation mask set then that will also dictate what satellites the roving receiver will use as it can't use satellites that coorections aren't transmitted for. Similar with dGPS systems as the reference receiever also has masking set and besides they only transmit corrections for a maximum of 9 satellites in any case. Augmentation systems really induce a masking cut-off angle by default. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Anders:Soooo, what's your "fair idea" then, if we come down to some good old numbers? 5°? 10°? I'm not aware of any hard-wired greater than 10 degrees and some are around 5 and then 0 degrees is fairly common (actually very common). For serious GPS observations the minimum is normally 15 degrees and even as high as 20 degrees for some applications but these receivers are configurable. Catch 22 with WAAS is the higher the mask cut-off the less chance of receiving these at low horizon latitudes. I'm not that sure if WAAS transmits corrections for all satellites in view (even if both base and roving receiever were seeing the same sats). With WAAS the base receievers have an elvation mask set then that will also dictate what satellites the roving receiver will use as it can't use satellites that coorections aren't transmitted for. Similar with dGPS systems as the reference receiever also has masking set and besides they only transmit corrections for a maximum of 9 satellites in any case. Augmentation systems really induce a masking cut-off angle by default. Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, that's right, they don't but then not many do, so I suppose the next question is WHY not. I believe there's a lot of "little" things that users of consumer grade receivers aren't told. Some manufacturers won't confirm some of the things that are "known" but then they don't/won't deny them either. I've a fair idea what your etrex mask is and I see no reason why it's not mentioned in the specs? Cheers, Kerry. I never get lost everybody keeps telling me where to go

Anders, that's right, they don't but then not many do, so I suppose the next question is WHY not. I believe there's a lot of "little" things that users of consumer grade receivers aren't told. Some manufacturers won't confirm some of the things that are "known" but then they don't/won't deny them either. I've a fair idea what your etrex mask is and I see no reason why it's not mentioned in the specs? Cheers, Kerry. I never get lost everybody keeps telling me where to go

The term GPSr is used to cover a fairly wide description of device capabilities. In terms of accuracy, all handheld GPS receivers are created equal, they have the same basic parts and use the same basic signals. It is what they do with what they get that makes the difference (to a point). The "which is best" type question appears to be more directed to the "general" user type interface, which is really only taking a continuous feed of positions from a "GPS engine" and turning those positions in something that are useful and meaningful to the user. This GPS engine has its own built in firmware/software (apart from the main "user" software/firmware), which can also have some user control from user system but in many cases especially in the cheaper units (like many handhelds) configurations are hard-wired. Even though one receiver might use all satellites down to the horizon another with the same engine might be hard-wired to a mask out satellites below a specific cut-off angle. In practice there might not be a lot in it but technically the masked out lower satellite model is the better option but not many users would be aware of what models have what masking cut-offs and why. Most are too tied up in the the 12 channel myth/more satellites the better syndrome. Obviously there are other "refinements" in the engine function (and also the antenna) that does/might/could make some difference, which might not be immediately obvious to most users. Cheers, Kerry. I never get lost everybody keeps telling me where to go

The term GPSr is used to cover a fairly wide description of device capabilities. In terms of accuracy, all handheld GPS receivers are created equal, they have the same basic parts and use the same basic signals. It is what they do with what they get that makes the difference (to a point). The "which is best" type question appears to be more directed to the "general" user type interface, which is really only taking a continuous feed of positions from a "GPS engine" and turning those positions in something that are useful and meaningful to the user. This GPS engine has its own built in firmware/software (apart from the main "user" software/firmware), which can also have some user control from user system but in many cases especially in the cheaper units (like many handhelds) configurations are hard-wired. Even though one receiver might use all satellites down to the horizon another with the same engine might be hard-wired to a mask out satellites below a specific cut-off angle. In practice there might not be a lot in it but technically the masked out lower satellite model is the better option but not many users would be aware of what models have what masking cut-offs and why. Most are too tied up in the the 12 channel myth/more satellites the better syndrome. Obviously there are other "refinements" in the engine function (and also the antenna) that does/might/could make some difference, which might not be immediately obvious to most users. Cheers, Kerry. I never get lost everybody keeps telling me where to go

you mean I have to find something to know what I'm talking about. Until then the score says at zero (is that least enough) which is a good average don't you think Actually it will always be zero but then I'll talk to anybody (even you) just 'cause I can. Cheers, Kerry. I never get lost everybody keeps telling me where to go

you mean I have to find something to know what I'm talking about. Until then the score says at zero (is that least enough) which is a good average don't you think Actually it will always be zero but then I'll talk to anybody (even you) just 'cause I can. Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by BassoonPilot:... You may have noticed I used the word "approximately." Considering the several factors that affect the accuracy of gpsrs both at the time a cache was placed and our attempt to find it, I think "5 feet per (third decimal place) tick" is a close enough _approximation_ for "field use" while geocaching. now being "approximate" would that be 5 feet per third decimal place in total or 5 feet per third decimal place both ways Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by BassoonPilot:... You may have noticed I used the word "approximately." Considering the several factors that affect the accuracy of gpsrs both at the time a cache was placed and our attempt to find it, I think "5 feet per (third decimal place) tick" is a close enough _approximation_ for "field use" while geocaching. now being "approximate" would that be 5 feet per third decimal place in total or 5 feet per third decimal place both ways Cheers, Kerry. I never get lost everybody keeps telling me where to go

A receiver's update rate/time is only as good (limited) as the hardware/software that's driving it. Some units that spec 1 second updates (maximum) can have a hard time achieving "true" 1 second updates anyway. There is a difference between the actual position update rate and the way these positions can be recorded. In recording data the data some units can be configured on a time or distance moved basis but this should not be confused with position update rates, which by the way some units can also specifically configure. Cheers, Kerry. I never get lost everybody keeps telling me where to go

A receiver's update rate/time is only as good (limited) as the hardware/software that's driving it. Some units that spec 1 second updates (maximum) can have a hard time achieving "true" 1 second updates anyway. There is a difference between the actual position update rate and the way these positions can be recorded. In recording data the data some units can be configured on a time or distance moved basis but this should not be confused with position update rates, which by the way some units can also specifically configure. Cheers, Kerry. I never get lost everybody keeps telling me where to go

There is software that does this but it's generally not free. Don't even need a GPS as updated almanac files (depending on the software) are generally available for download. One is certainly always going to get some sort of satellite signal (we would hope) but the difference between say 3-4 sats and 10 is quite considerable when one considers geometry, reception, accuracy (to a point), obstructive influences and other issues. This is probably one of the more important facets of planning to be in the right place at the right time (to make the most of the available conditions) as certain times of the day (and it can vary from day to day) can/are better than other times. http://www.cqnet.com.au/~user/mattk/gps/gps_plan.htm Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on October 02, 2002 at 02:30 PM.]

There is software that does this but it's generally not free. Don't even need a GPS as updated almanac files (depending on the software) are generally available for download. One is certainly always going to get some sort of satellite signal (we would hope) but the difference between say 3-4 sats and 10 is quite considerable when one considers geometry, reception, accuracy (to a point), obstructive influences and other issues. This is probably one of the more important facets of planning to be in the right place at the right time (to make the most of the available conditions) as certain times of the day (and it can vary from day to day) can/are better than other times. http://www.cqnet.com.au/~user/mattk/gps/gps_plan.htm Cheers, Kerry. I never get lost everybody keeps telling me where to go [This message was edited by Kerry on October 02, 2002 at 02:30 PM.]

quote:Originally posted by Anders:Oops, were you listening, Kerry? Anders NO only listen to every second word (on average) Snow what's snow now if it snows here then we've got a problem Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Anders:Oops, were you listening, Kerry? Anders NO only listen to every second word (on average) Snow what's snow now if it snows here then we've got a problem Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cache Canucks:.... when compared to the more nitty gritty issues (like a *real* altimeter and waypoint averaging to name but two...). waypoint averaging is a "nitty gritty issue" Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by Cache Canucks:.... when compared to the more nitty gritty issues (like a *real* altimeter and waypoint averaging to name but two...). waypoint averaging is a "nitty gritty issue" Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by CreagerStone Family: I'm leaning towards the eTrex Legend instead of the SporTrak Map for the following reasons: ..... ..... - I'm a little ticked at Magellan for leading me to think the Pioneer was a 12 channel receiver with the "AllView 12" designation ..... What has the specifications of a 5 year old receiver got to do with this decision. Getting away from the 12 channel myth for a moment that's the way things (generally) were "back then" and there were other instances of that similar ploy with different manufacturers. The 12 channel myth do you really think 12 channel receivers are more accurate simply because that are 12 channel Cheers, Kerry. I never get lost everybody keeps telling me where to go

quote:Originally posted by CreagerStone Family: I'm leaning towards the eTrex Legend instead of the SporTrak Map for the following reasons: ..... ..... - I'm a little ticked at Magellan for leading me to think the Pioneer was a 12 channel receiver with the "AllView 12" designation ..... What has the specifications of a 5 year old receiver got to do with this decision. Getting away from the 12 channel myth for a moment that's the way things (generally) were "back then" and there were other instances of that similar ploy with different manufacturers. The 12 channel myth do you really think 12 channel receivers are more accurate simply because that are 12 channel Cheers, Kerry. I never get lost everybody keeps telling me where to go