GPS Waypoint Coord. Sources

[blacklab2020]

When it comes to putting waypoints into your GPS unit for the whites. Are first hand experience coord, such as those on chauvin-guides site the best, or the coordinates from the toposoftware (i.e. garmin mapsource), OR both in such a way as not to confuse the two?

I realize there may be inter-instrument variability, poor triangulation from the first hand coordinates such as those on the chauvin guides site.

Though there may also be error in the mapsource CD.

In your experience, have any of you found one to be better than the other?

~Justin

 

[NH_Mtn_Hiker]

So far I've had good luck using Worldwind 1.3

Personally, I've little use for Garmin Mapsource. Some of their waypoints have been off considerably.

 

[sardog1]

I realize there may be inter-instrument variability, poor triangulation from the first hand coordinates such as those on the chauvin guides site.

There shouldn't be any "inter-instrument" variability noticeable to any user. What you might see is another user not waiting long enough for the most precise fix possible before recording a point. The recorded point might be several yards/meters away rom the described point in that event.

But even with that possbility, I would personally always prefer the field-recorded point from someone as reliable as Chauvin Guides over something plucked off a publisher's software. (I agree that Mapsource can be kind of problematic at times.) The one time you really need accurate waypoints is in whiteout or nighttime conditions on a hazardous route. The rest of the time you can more easily check the waypoint against the map and terrain, which you're doing all the time anyway, right?

 

[DougPaul]

There shouldn't be any "inter-instrument" variability noticeable to any user. What you might see is another user not waiting long enough for the most precise fix possible before recording a point. The recorded point might be several yards/meters away rom the described point in that event.

There shouldn't be any systematic error in GPS instruments, but such has happened with altitude. (Altitude requires geoid (planet shape) models--errors have occurred in these models.) Any situation where two GPSes use different references or datum conversions will appear to the user as systematic differences. Also, a correct earth-centered coodinate could be converted incorrectly to a datum before it is reported to the user (a program error).

In practice there are always random errors. The EPE (estimated position error) attempts to quantify these errors.

But even with that possbility, I would personally always prefer the field-recorded point from someone as reliable as Chauvin Guides over something plucked off a publisher's software. (I agree that Mapsource can be kind of problematic at times.) The one time you really need accurate waypoints is in whiteout or nighttime conditions on a hazardous route. The rest of the time you can more easily check the waypoint against the map and terrain, which you're doing all the time anyway, right?

The Chauvin Guides waypoints are NAD-27 datum, taken from the USGS topo. If one entered these waypoints into a GPS using a WGS-84 datum, the error would be about 230meters--enough to be significant in poor visibility. (I don't know if the waypoints were taken by hand from a paper map or using NG TOPO!. As of the last time I checked, this info is not on their website. (I exchanged some email with Marc Chauvin about the datum. He has NG TOPO!, but I don't know if it was used to obtain these waypoints.))

To get waypoints, I just use Garmin Mapsource US Topo or 24K Topo, place waypoints wherever I want them, assemble them into whatever routes I desire, and transfer them electronically into my GPS. Very fast and easy. Also minimizes the chance of human error.

If you have a mapping GPS with the appropriate maps loaded, you can load waypoints in the field just by moving the pointer to the desired location and pressing the appropriate button. (I have done this on long trips when I didn't have access to my computer.)

Doug

 

[blacklab2020]

Thanks Doug. That is really helpful to know about the chauvin coords. I have the topo software for mapsource and have waypoints entered from the software to the gps. I also programmed waypoinnts manually from the chauvin site. I have then named each point with the suffix CG or MS to distinguish between the two sources. In addition when I am out there I plan to mark each location with my own instrument and keep note of the accuracy at the time of triangulation.

Regards,
Justin