I stood on the crest of the levee and moved N-S until I was due east
of the witness monument according to the GPS. With a GPS error of 18
feet and a distance of 540 feet to the levee, the maximum error in the
bearing would be arcsin(18/540), or about 1.9 degrees. Plugging this
back into the 80 ft measurement yields a maximum N-S error at the
trifinium of about 32 inches, less than the breadth of my arms which
were outstretched to avoid falling into holes or tripping over rocks,
rattlesnakes, etc.
I paced the 80 feet from the witness monument to the trifinium, which
probably had an accurancy of +/- 10%. It coincided with the "zero"
point on the GPS (whose accuracy is determined by a circle of 18 foot
radius, or about +/- 23% over 80 feet. I then continued the walk to
the center of the river along the E-W line to increase the probability
that I crossed the trifinium regardless of its actual position. I
estimated the 9 chain distance by GPS and visual position in the river
relative to the riverbanks.
BJB
--- In BoundaryPoint@yahoogroups.com, "acroorca2002" <orc@o...> wrote:
> oops me too
> as i inadvertently cropped the rock i meant to show you
> thinking to save bytes
> dohh
>
> & am still tweaking my crazy scanner to give you a better fix on it
> as well as a better quality scan
> but for now suffice to say the subject in that pic is standing about
> a yard north of a visible rock
> albeit not as visible as the rock in your 80 foot pic
>
> & since i only recall the one rock
> & like yourself also recall how near & yet so far it seemed from
> the target point depicted on the topo
> i think it is probably the same rock as appears in the foreground
> of your 80 foot pic
> presumably exactly upon the ndsd line there
> but i cant be sure it is the same rock because the grass was
> taller when i visited
>
> & if it is the same rock
> i think it probably hasnt moved much in the interim
> but cant even be sure about that
>
> & since the witness marker appeared to have been so rough
> hewn as well as frost heaved
> & its north & south faces looked unreliable for gauging due east
> i disregarded them for getting my best available bearing
> as i trust you also did
>
> indeed i am just assuming your instrumentation gave you a
> better fix on the true bearing of the ndsd line than i ever got by
> shooting the sun
> or rather by trying to replicate the bearing of the access road
> since the grass on it was over the roof of my truck
>
> also i am pretty sure the season was september
> & the descending sun brilliant enough to have still been several
> degrees above the horizon & thus several degrees south of its
> setting point at the moment the picture was made
> which is why i made this class b photo try
> as i recall
> a bit south of the shadow of the witness monument
> yet apparently still a bit north of your rock
> or my rock
> or our rock
> as the case may be
>
> so i imagine we are talking maybe 5 degrees of disagreement
> one way or the other rather than anything like a 180
> tho i realize i too am quite capable of a 180
> hahaha
>
> & my 80 feet was measured by pacing rather than tape measure
> & without hesitation or regret given the cartographic parameters
> so that could explain why it seems maybe 10 percent short when
> compared to yours
> if indeed it can be compared to yours
> etc
>
> but anyway
> how did you get your due east bearing & your measurements
> & within what level of accuracy would you estimate them
>
> --- In BoundaryPoint@yahoogroups.com, "bjbutlerus"
> <bjbutler@b...> wrote:
> > Oops, please disregard my previous post. It was 180 degrees
> out of
> > phase. Was this picture in spring or fall? I don't think it could
> be
> > a summer shot because your shadows are cast to the north,
> implying
> > that the sun is setting south of west.
> > BJB
> >
> > --- In BoundaryPoint@yahoogroups.com, "m donner"
> <maxivan82@h...> wrote:
> > > thanx brian
> > > & you may remember the attached pic from the paleo corner
> corner
> > >
> > > it records a topo assisted but zero tech 20th century class b
> try
> > for mnndsd
> > > made actually with eyes closed
> > >
> > > note position of rock in ground at that time
> > >
> > > the photographer jc appears in shadow to sit crosslegged
> atop the
> > witness
> > > monument
> > > as she creates the pic of the pointer meditating upon the
> point
> > > & making a virtue of having to squint one eye at the sunset &
> the
> > other at
> > > the bugs anyway
> > > & with his shadow similarly hyperextended for maximum
> possible
> > coverage in
> > > the moment point
> > >
> > > golden epiphenomena also grace this unretouched photo
> > >
> > >
> > > of course jack & joyce & clark arrived earlier still
> > >
> > >
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