[Tagging] Way beneath overhanging cliff

[Kevin Kenny]

On Tue, Oct 3, 2017 at 8:41 PM, Bill Ricker <bill.n1vux at gmail.com> wrote:

> This obviously doesn't qualify as a tunnel since the ?north? side is open to
> air; nor is it a cave, quite.  Do we have a way attribute or area attribute
> for  undercut/overhang area ?

"covered=yes", I think...

>> And, yeah, 'natural=cliff' is on the "to do" list. I've only recently
>> started adding those, since when I render my own maps, I use
>> contour lines from NED. ("Cliff" is still nice to have, since
>> topographic features lurk in between the contours.)
>
>
> Yes please.
> The contours in Cycle Map rendering do not suggest a cliff in your original
> linked location,  although  name "Escarpment Trail" does hint at it. (But
> all too often, a trail is named for an *endpoint* not the view on the way,
> so should be at best inconclusive.  :-)

I've noticed that the data source for Cycle Map's contours pretty much
never shows cliffs. They seem to get interpolated away.

The USGS map https://caltopo.com/l/BUQ1 shows what's going on
if you know how to read it. If you look by Mine Lot Falls, you'll see
that some number of 20-foot contours disappear because they're
overhung, or because it's too steep to draw them.

> Re old-school transit etc - yes, packing serious surveying gear (either
> antique theodolite or modern computer/laser "total station") into the
> boonies requires packmules, grad students, or Scouts you can pay in beef
> stew, as well as a qualified operator. I'm trying to recruit some of same
> for an educational, non-mapping project ...
>    OTOH, a non-survey "construction-grade"  100' tape measure or rolling
> wheel and either an orienteering (infantry) compass or a Boonton  "pocket
> transit" (engineers/geologists) compass might be adequate to measure heading
> of trail at vertical occlusion, bearing and distance along trail from a
> point with good GPS posit to each occlusion point, and then to inflection
> node under cover and distance between, to improve your level=-1  track.
>    Alternatively, you can hunker-down with a good GPS (advanced user modes)
> at each angle of the occluded trail, switch to Constellation view, and wait
> until the GPS constellation gets lopsided into the narrow wedge of sky you
> *can* see from there and get your best posit then. Quality will still be low
> due to short baseline in sky but will be better.
>    Or try both ...

Uhm, yeah. The GPS solution doesn't work too good, I've sat still under
Mine Lot Falls waiting, and never got a usable position. Even when there
are enough satellites in sight, the receiver gets confused by specular
reflections off the rock face. That rock is pretty smooth in L band.

I have a Brunton mirror-sighting compass, a plane table, a rod and
a tape. What I don't have is a crew. You need someone to hold the
sighting rod, someone to sight, and two guys to work the tape.
For the Ladder itself, I'd need to do division of levels, or cosine
error would kill me.

So many projects, so little time...

> 73
tnx es vy 73 to you also,
de ke9tv/2,
Kevin