ok many thanxxx again ron for all these gratifying corroborations
i believe we are in complete synch now too
& your scrutiny has been instrumental in helping me to
understand exactly why we are not & cannot really be reaching
for the correct inch or less here but only for the correct foot
thus far anyway
if we had the intermonumental caus sight line to use
we would of course be able to reach for the right inch & beyond
indeed we might even hit the correct millimeter
despite the 10000 to 100000 fold disparity in our triangulation
which runs kilometers while rising only decimeters or
centimeters
for i believe such a sighting from monument 194 to 195 across
the idwa meridian may yet be possible with hi power binocs
next time 2 people visit there
one of them to hold the binocs & direct the fingertip of the other
north or south along a yardstick to the true sight line intersection
but until then
tho we have the idwa hairline in plain view on the 1909 disk
& tho we wont be losing sight of it between there & true bcidwa
however many inches north it really lies
our best available caus line is not a visible hairline at all yet
but only a theoretical ribbon stripe the width of a full centisec or
statute foot
we might visualize this ribbon as a mini clearcut
about as wide as or a bit wider than the monuments themselves
running down the middle 5 percent or so of the actual clearcut
& until & unless we achieve our caus sight line
the truest available bcidwa is not a hairline intersection but only
the computational intersection of the idwa hairline with this
theoretical caus ribbon
& this intersection i have computed
crudely but i think entirely effectively
as the approximate foot centered 1 foot due north of the 1909
disk center
i myself have subsequently tried to refine this down to inches too
& in fact at one point i revised my guess to the approximate foot
centered 18 inches due north of the disk center
but now that i have reviewed the data so critically with you
i think my attempt to do so was misguided
& i have recentered my best guessed foot at 1 foot due north
for this is the limitation of accuracy that is built into the ibc coords
& i dont believe any tweaking of computational accuracy will
improve on it
i will of course be happy to improve on it
but i dont think it will really be possible til someone actually
reaches monument 194
or until the ibc upgrades their marker coords to millisecs or
beyond
--- In
BoundaryPoint@yahoogroups.com, "Ron McConnell"
<rcmcc@e...> wrote:
>
> "...daves report roughly midway down the page
>
> <http://tinyurl.com/6zgwc> "
>
> Ah. A key message I apparently overlooked while out of town.
> That answers some questions I asked in a later message.
>
> "...limit our overall degree of certainty
> to 2 decimal places..."
> Yep, at best 2 places.
> My programs use about 12 digits total
> for deg min sec and other calculations.
> BUT, it can't make the output better
> than the output.
>
> "..the submillimetric exactitude of your solution
> here below seems to indicate that you dont agree..."
> I believe we are on the same page and same song.
> One way to try to preserve the 2 places input
> is to do the arithmetic to at least one more
> and then round to 2 at the end.
> The program just shows all the digits.
>
> > But, how to find the north-south distance from
> > a 3rd point to an intermediate point on the line
> > isn't obvious.
>
> "ok but i still think it is obvious
> at least within the above stated parameters of exactitude
> it seems entirely reducible to a simple ratio computation"
> True for the short distances in this problem,
> but for the general case where the points
> are a lot further apart plane trig stops working
> and spherical trig has to be used, as in the formula
> (which works for short and long if one is careful
> to account for the special cases).
>
> > ==========================
> >
> > RCMcC
> > Angles and Distance greatly distorted.
>
> "what do you mean specifically by the above comment?"
>
> Just that it's hard to draw a triangle
> that's 3212 meters long and only 0.08 meters tall.
>
> >
> > [194] -- 3212 m -- I -- [195]
> > \ | /
> > 2946 m 267.048 m
> > \ /
> > [LSAW 5]
> >
> > ==========================================
>
> "> Given (all NAD-27 converted to NAD-83 with CORPSCON )
> >
> > Monument #194 = Point 1 = Lat1/Long1 = N 48.999056º W
> 117.072683º
> > Monument #195 = Point 2 = Lat2/Long2 = N 48.999215º W
> 117.028771º
> > LSAW#5 plaque = Point 3 = Lat3/Long3 = N 48.999197º W
> 117.032421º
>
> "but i think your 6th digit may be questionable
> for points 1 & 2"
>
> Maybe so. I used all the NAD-27 digits
> to feed into the standard CORPSCON translator to NAD-83
> and then rounded that output off to 3 digits
> to try to keep as much as possible until after
> all the number crunching.
> The final result after all calculations for Point I
> on the boundary is only good to 2 digits - at most.
> Then one should also round points 1 and 2.
>
> "...crediting such exactitude as you are delivering..."
> The math is just manipulating a model of physical reality.
> When physical reality is different from all the
> digits put out by the computer,
> physical reality rules
> and you try to correct the model.
>
> "...someone who understands all this ..."
> Gotcha fooled. :)
> I'm definitely not a pro at this stuff,
> just someone who has fiddled with it in spare
> time for a long time trying to keep the models
> (borrowed from the _real_ pros) as accurate as possible
> when crunching the numbers through a computer.
>
> I've studied a lot of sloppy programs
> where someone encoded a formula from a textbook
> into a computer program and had no idea
> what its limitations were and how the limitations
> of the computer arithmetic affected it.
> The GUIs looked great, though.
>
> A few years ago I was reading a program
> where I found that the programmer had
> twice typed in the value of pi as
> 3.141592818
> where the three digits "818" after the "2" are wrong.
> Fortunately, in his particular case it made
> no real difference, but if he were trying
> to calculate distances down to inches,
> as we are attempting here - no good.
> I guessed that he may have obtained
> the wrong value of pi from the MS Windows calculator.
>
> We are going out of town tomorrow and it may be
> Monday before I get to check in again if I miss
> in the morning.
>
> Have fun.
>
>
> Cheers, 73,
>
> Ron McC.
> w2iol@a...
>
> Ronald C. McConnell, PhD
>
> WGS-84: N 40º 46' 57.6" +/-0.1"
> W 74º 41' 22.1" +/-0.1"
> FN20ps.77GU31 +/-
> V +5058.3438 H +1504.2531
>
> http://home.earthlink.net/~rcmcc
>
> There are 10 kinds of people.
> Those who understand binary arithmetic
> and those who do not.