See my several insertions below, the last one being the long one.
Lowell G. McManus
Leesville, Louisiana, USA
----- Original Message -----
From: "aletheiak" <aletheiak@...>
To: <BoundaryPoint@yahoogroups.com>
> yikes
> what makes yall think we are lost
> in anything
Forgive me. When I wrote "lost in all these maths," I didn't mean "lost" in the
sense of unable to find your way, but rather "lost" in the sense of "lost in
love" or "lost in bliss." Clearly, you derive more bliss than most from being
engrossed in complex maths. To each his own.
> but anyway
> please bust anything you know is lost or wrong
> directly
>
> no need to strut or pussyfoot around first
> whichever it is
It is neither.
> we are seeking the best available truth here on principle
>
> & if you can indeed advance our try for true bcidwa
> or can even just tell us how we can
> or can tell us how anyone can
What I can do is tell you "how someone can"--that someone being a surveyor.
> why are yall standing on the ceremony of waiting for a request
> yikes
It was already late at night, and I was trying in vain to find local lodgings
for New Orleans friends fleeing the hurricane. I also didn't want to waste my
time explaining something that you might already know, only to learn later that
you were as interested in the theoretical maths as in practical measurement on
the landscape.
> also
> or perhaps first
> we already know there is a difference between what pros can do
> & what we ourselves have so far been able to do
True. I disclaim being a professional surveyor, but I did take a one-semester
civil engineering course in land surveying as an elective in 1974. I have dug
out my textbook (copyright 1969) from that course and reviewed what I will
explain below. Obviously, the instruments from that era were not the lasers of
today, but the principals are the same. It is interesting that this task is all
measurement without any complex maths involved.
> but what do you mean by sufficient
I mean equal to the usual standards of land surveying.
Now, here's the explanation:
If you will look at the topo map at http://tinyurl.com/6339v , you will see that
CAUS boundary monument 195 is approximately 900 feet east of BCIDWA. The 195
monument is a bit less than 120 feet higher in elevation than the tripoint,
being out of sight just over the top of a ridge. (The contour interval is 40
feet on the US portion of this map.) If you will pan west one iteration, you
will see that CAUS monument 194 is 663 feet higher than 195, on a much higher
ridge approximately two miles west. Of course, the CAUS monuments are
intervisible, and the boundary is defined as the line of sight between them.
The trouble is that 195, at least, is not visible from the tripoint.
For those who don't know, the instrument called a transit is a telescope (with
crosshairs) mounted such that it can be rotated on axes in two planes: around in
the horizontal plane and end-over-end in the vertical plane. The transit is
mounted on a precisely levelable base that sets atop a tripod. A plumb line
hangs from the center of the instrument between the tripod legs. The most
precise transits are called "theodolites." The textbook says that the best
ones, reading to .1 second, could theoretically measure the angle between two
points an inch apart at a distance of 40 miles. There are probably modern laser
devices that do the same. Note that in our current problem, we are not
measuring any angles at all, but merely using the leveled transit for sighting.
The ideal situation here would be for the surveyor to set up and precisely level
his transit directly over CAUS 195. (If the monument is too tall for this, he
would use the process described in the next paragraph.) He would sight monument
194 on the very high ridge to the west. Next, he would rotate the telescope
down to the near ridge just west of 195 and direct his rod man to establish a
point on CAUS atop this ridge. He would move the transit to this new point,
backsight to 195, flip the telescope to 194 for an accurcy check, then rotate it
downward to sight the tripoint down the hill. The rod man would be directed to
the point there that is on CAUS some slight distance north (we assume) of the
existing IDWA cairn.
If the transit cannot be set up over 195, the surveyor will use a process called
"balancing-in" to establish a point in-line between two known points. The
surveyor would set up his transit on a trial point in the approximate middle of
the clear-cut vista on the ridge between the tripoint and 195. Ideally, he
should have visibility of both. He would take sightings backward and forward to
194 and 195 and move his trial point as required until he has the transit
precisely on the line. The fine adjustments are made in the "shifting head"
between the tripod and the transit. When the placement is correct, he will
rotate the telescope downward to the vicinity of the cairn and have his rod man
establish the tripoint as above.
If monument 194 is visible from the tripoint, forward and backward sightings
could be taken from the tripoint for confirmation. If not, the line could be
continued westward until 194 is visible.
This is my best understanding of what I read.
> In BoundaryPoint@yahoogroups.com, "Lowell G. McManus"
> <mcmanus71496@m...> wrote:
>
> > I hope y'all realize that while you're lost in all these maths, any
> competent
> > surveyor with a transit and a rod man could locate BCIDWA
> with sufficient
> > accuracy on the line-of-sight CAUS in less than a half-hour
> from CAUS monument
> > 195 (which is only about 900 feet away) even if neither
> monuments 194 nor 195
> > are visible from BCIDWA.
> >
> > I can explain how on request.
> >
> > Lowell G. McManus
> > Leesville, Louisiana, USA