GPS best practices for low visibility?

[BillK]

Greetings,
Can someone please educate me on what some of the best practices are for using your GPS to navigate out of a low-visibility situation? I just recently purchased the NG TOPO software and I do own a Garmin etrex Vista GPS, but I don't have much experience with using either. I've played around with the Garmin Tracback feature, waypoints, etc., but I'm curious as to what others are doing to prepare for a situation where there may be limited visibility, such as on the summit of Washington. I would like to perform a winter hike on some of the northern presidentials, but I'm very concerned about not being able to find my way back due to low visibility. From what I've been able to research, it appears that a common practice is to load various waypoints into your GPS from key locations, and then use the find/goto feature from within the GPS
to navigate to those waypoints. Since I don't yet have a data cable to download the waypoints, I suppose I could get the waypoint coordinates from my topo map, and then manually punch them into my GPS?
Thanks in advance for sharing your knowledge and experience on this subject.

 

[NH_Mtn_Hiker]

...it appears that a common practice is to load various waypoints into your GPS from key locations, and then use the find/goto feature from within the GPS to navigate to those waypoints...

That's what I do. It's simple and reliable, provided the waypoints you load are accurate. I use NASA's Worldwind for my waypoints. I often double check the waypoints with Topozone. I've found both to be more accurate than some of the commercially available mapping software available. Garmin's MapSource is one of those that's know for it's inaccuracy.

I love my Vista.

 

[DougPaul]

GPS navigation is similar to to compass-based point-to-point navigation, except you can usually tell exactly where you are between the known waypoints. You also have the capability of placing electronic waypoints in your GPS and navigating to/between them.

I suggest that you read one of the books on the topic.
http://www.rei.com/online/store/Sea...angId=-1&storeId=8000&query=GPS+books&x=0&y=0
brings up a list.

Sam Wormley has a nice-looking list of online tutorials:
http://www.edu-observatory.org/gps/tutorials.html

The following search also brings up a bunch of online tutorials--you might check them out:
http://www.google.com/search?hl=en&q=GPS+navigation+tutorial&btnG=Google+Search

I see you have an eTrex Vista--you might find Garmin Mapsource Topo USA or 24K for your local region useful because it will allow you to load topos into the GPS. Your current location will be shown on the topo.

Doug

 

[BillK]

Thank you for the information. I'm going to pickup an interface cable and experiment with uploading waypoints/routes to my GPS. I'll compare how accurate my map is during my next hike. It appears to be very accurate as I went outside of my house and took my current position with the GPS (Lat/Long), and then transferred that information to my TOPO map manually, and it looked to be dead-on as to where my street/house was located. I'd feel more comfortable testing the accuracy on a mountain however.

 

[DougPaul]

OK.

I suggest you also get Garmin Mapsource Topo. Loadable 1:100K topo maps for the entire USA. Loading the topo map into the Vista will make it even more useful.

(NG TOPO! is great to look at and use for planning, but cannot load maps into a GPS. It just does waypoints, routes, and tracks.)

Doug

 

[nartreb]

before heading out in the dark/fog...

A word of warning about using a digital map in your GPS unit: the map may be out of date or just plain wrong. Mountain topography should be accurate, but trails may not be located where your GPS thinks they are. Always double-check the indicated trails against a map you know is good. In my experience, Topozone is way out of date, but the maps in the AMC White Mountain Guide are very good. I don't know about Topo!.
A few trails to check for accuracy (moved in the past few decades or just plain wrong on some maps): Osseo Trail, North Twin Trail, bottom of Flume Slide Trail, Livermore Trail (formerly Livermore Road). If your map disagrees with Topozone on all of these, your map is probably a good one

 

[Remix]

I have had good luck by pre-programming the following way points: shelters, trail junctions, and water using NG Topo.

I was hiking up to the Brown Mountain LT at night.
I was prepared for the showers, but not the fog. Visibility was no more than a few feet, and I had not been there before.

I continued on, consulting my GPS when I thought I should have made it to the LT. I was close and guided myself in. And I nearly tripped over floor of the LT, because I thought the fire ring outside the LT was a cairn.

 

[BillK]

Doug,
Does Garmin Mapsource Topo include coverage of all the hiking trails in the Whites? Assuming that I got this at some point, is this something that I would load completely into my GPS, and then use my NG TOPO software to create routes, waypoints, etc. to upload over the top of the Garmin Mapsource maps? I guess I'm tryinig to understand if they somehow complement each other, or do I really just need the Garmin software to do it all? I've already purchased the NG TOPO software and I had planned on downloding routes and waypoints from that primarily for the purpose of getting me out of a low-visibility situation. (Find my way to the next closest waypoint when I can barely see my hand in front of my face) Thanks for your valuable feedback on this.

 

[BillK]

Thanks REMIX, Have you found the pre-programmed waypoints from TOPO to be very accurate? Earlier this morning I pre-programmed a waypoint into my GPS manually that I had gotten from NG TOPO, (End of an off ramp about 11 miles from my house) I was happy to find that when I had gotten to the end
of the off ramp, I was within 20-30 feet of the waypoint. Although I've never tested it on a mountain, it appears to be very accurate for locations close to my house so I'm cautiously optimistic.

 

[DougPaul]

Doug,
Does Garmin Mapsource Topo include coverage of all the hiking trails in the Whites? Assuming that I got this at some point, is this something that I would load completely into my GPS, and then use my NG TOPO software to create routes, waypoints, etc. to upload over the top of the Garmin Mapsource maps? I guess I'm tryinig to understand if they somehow complement each other, or do I really just need the Garmin software to do it all? I've already purchased the NG TOPO software and I had planned on downloding routes and waypoints from that primarily for the purpose of getting me out of a low-visibility situation. (Find my way to the next closest waypoint when I can barely see my hand in front of my face) Thanks for your valuable feedback on this.

Garmin Mapsource Topo (GMT) is based upon the USGS 1:100K scale topos (as are level 4 of NG TOPO!). Hiking trails are marked, but is has been some time since the maps were updated, so recent changes are not shown. (On the other hand, the old trail locations are useful to a bushwacker.) There are a few spots where the trails are missing. The primary advantage of GMT over NG TOPO! (NGT) is that the maps can be downloaded into the GPS. (Your eTrex Vista has 24MB of mapping memory.) Once you have used a mapping GPS you will never go back...

Both GMT and NGT will transfer waypoints, routes, and tracks to and from the GPS.

I have both GMT and NGT and find them both useful. (I also have Garmin Mapsource 24K Topo East for a bit more detail in the Whites.)

When I plan a trip, I enter the waypoints of interest into my computer, connect a subset of them into my planned route, and download to my GPS. (I keep a standard load of hiking maps in my GPS, but I will load in a special set if required for the hike.) I also check the AMC maps for any changes in the trail locations. In doing this, I familiarize myself with the map and the region. (As a result, I rarely need to consult the map in the field.)

If I change my route in the field, no problems with the GPS. I just use the map and, if need be, ignore the pre-programmed waypoints. (One can add waypoints in the field easily by simply moving the pointer over the spot and pressing in the click stick ("enter") if needed.)

Garmin has a map previewer on their website--check it out if you want to see what their maps are like.

As for accuracy, all maps have some errors. (I have posted the USGS topo accuracies previously--don't have time to search for them right now.) Add the map errors to the GPS errors and you cannot expect to always trip over your destination. But you should have little difficulty getting within shouting (easy visual search) distance.

Doug

 

[DougPaul]

Thanks REMIX, Have you found the pre-programmed waypoints from TOPO to be very accurate? Earlier this morning I pre-programmed a waypoint into my GPS manually that I had gotten from NG TOPO, (End of an off ramp about 11 miles from my house) I was happy to find that when I had gotten to the end
of the off ramp, I was within 20-30 feet of the waypoint. Although I've never tested it on a mountain, it appears to be very accurate for locations close to my house so I'm cautiously optimistic.

Typical GPS accuracy: up to 10 meters. (The GPS can show you the EPE--Estimated Position Error. If all else is perfect, there is a 95% probability that the GPS reading is less than that distance from the actual location. However, all else is frequently not perfect and in practice, the errors can be much greater, for instance in trees or in a tight valley.) WAAS approximately halves this error if everything else is perfect. (As stated elsewhere, I don't generally use WAAS when hiking.)

Map errors vary with the map. USGS topos are pretty good. (As noted in my previous post, I have posted the error specs elsewhere.) Garmin shows an error circle based upon the EPE and map accuracy on the map display if you zoom in close enough.

Doug

 

[mavs00]

Can someone please educate me on what some of the best practices are for using your GPS to navigate out of a low-visibility situation?

This is what I do. I own the software and have loaded all of topo (all of the ADK's) into my into my Vista (I owe one two). I usually preload waypoint when I b-whack, and then promptly ignore them when I get on the mountain an see what the actual terrain looks like. That topo stuff just doesn't show sublties like 15-20 foot cliffs that are easy to walk off in heavy cover. I then just use the Mapping mode (which shows my relative position on the topo map) to navigate my way to where I am going.

If I were in the situation you describe. Heading above treeline in low visibility, I would Ensure to use the "MARK" feature to place a waypoint at "critical" point of safety that you MAY have to navigate back to (i.e. such as the spot the trail exits the trees and enters the literal OCEAN of featureless terrain. Then, if you stepped got off the path, you could navigate back using the goto waypoint feature or simply the map mode to head to the "actual field data" waypoint you marked earlier. The map mode, with the software loaded, should help you avoid walking off Tuck's ravine too by being able to see surrounding terrain.

Plus if, while you were lost up there (if that were the case), and you came across a cairn or trail, the loaded data should also help to determine "what trail you found" and where it leads.

I don't hike the Whites often, so perhaps my advice is useless. But that's what I would do. I use the "Mark Waypoint" tons on my unit (more then preloaded data) to store locations of anything from nifty things I find along the way, to where I drop my pack for that "mad slackpack dash to the summit and back". Hey, you never know when that sunny sky will give way to zero vis.

 

[BillK]

Thanks mavs00. What TOPO software do you own? It appears that with NG TOPO, I don't have the capability to download all the maps, just waypoints/routes, thus I plan to just create a GPS route from within TOPO, say from above treeline to a summit, with various waypoints along the way, then if I was to lose visibility, try and use these waypoints/route to navigate myself back down to treeline. Does this sound like a reasonable approach?

 

[Remix]

I can't testify to the reliability of NG topo maps accuracy other than for that one anecdotal story. But they are based on official USGS quads, so I don't think you can do much better.

An important point that should be emphasized (and I did not) is to
1) not get into low visibility situations thinking that your GPS can help get you out.
2) not let your GPS be the only means of escape from poor visibility conditions.

They make things easier, not safer.

 

[DougPaul]

The specs for the accuracy of the USGS paper topos are as follows:
The 1:24K (or 1:25K) paper topo maps have the following accuracies:
* horizontal: at least 90% within .02 in on map (40 ft on the ground)
* vertical: at least 90% within 1/2 a contour interval

More info and references in the thread "Accuracy on electronic maps":
http://www.vftt.org/forums/showthread.php?t=7026

Doug

 

[weatherman]

Make sure it works in your expected conditions

Just to echo Remix:
This time of year, cold and moisture can do bad things to batteries. I experienced this on a hike last month, rendering our group's GPS nothing more than expensive ballast. Might be good to try putting your GPS in the freezer for a couple hours to see if it still works. If you can't see cairn to cairn when you pop out on top, good idea to consider trying again another time.
_Weatherman

 

[skidoc22]

addendum

My GPS eats batteries inthe cold (Magellan Meridian). I suggest Lithium batteries for the winter and for backup spares. I use rechargables for the primary batteries and if they die I have the Lithiums which are lighter and are said to last between 2 - 5 times longer and are minimally affected by cold. Slightly off topic but hope it's helpful.

 

[BillK]

Thanks to everyone for the great advice! See ya on the trails!

 

[Neil]

Excellent advice and links as usual. If I was doing Washington in winter I would be sure and carry a long piece of thin (ie. light) cord. If your gps buys the farm in a whiteout you can always tether a person and send them to look for the next cairn. Once they find it they tug on the line and forward you go. I have never had to do this but a member of this forum has done this in the MacIntyre range in the dacks. He said it worked very well and that without the rope, well....

This brings me to a question. How far apart are the cairns on Washington and environs?

 

[Remix]

I guess no one uses those bamboo sticks- or are they used for marking safe places to cross a crevasse?