--- In BoundaryPoint@yahoogroups.com, "Michael Donner"
<barbaria_longa@h...> wrote:

> actually several pleasant surprises this morning at topozone
>
> first
> the long awaited topos of puerto rico & the virgin islands are

finally being

> filled in
> & are now practically complete on at least one coverage level
>
> second
> it is apparently now possible to use the coordinate format

feature there to

> get geopositions down to the nearest integral degminsecs
> by simply clicking on any desired point
> wow
> & i say apparently only because i have previously found that the

purported

> accuracy levels of topozone may leave something to be

desired

>
> but whatever the actual range of error here of each stated

second of

> latitude & longitude
> we are now surely within a few hundred feet & hopefully within

100 feet of

> the truth
> even while we realize that the truth of the maritime tripoints will

> elusive in any case for a host of other reasons too

fortunately however
i just realized
an objective test of the accuracy of the topozone clickable
degminsec unit is readily available thanx to some data that were
previously developed for another maritime tripoint
oruswa
which is in fact the clearest & least elusive of the entire set of 20
since it is by chance pinpointed twice

first in bus&ss p155 & then by the most explicit topo depiction

http://tinyurl.com/3b5bu
is not a mistake or an abstract art work
but shows the click point at the maximum zoom level
& hence presumably at the greatest possible accuracy level

to see the state of the art depiction of the greater tripoint area
select the large size & zoom out to at least the 250000 level

& since we have already visited & studied oruswa quite carefully
in messages 4598 & 4713 & 4745
we can simply borrow the data from there & compute the critical
longitude figure alone
for there is actually no question about the latitude
n46d15m00s

&
begin drum roll
by exact calculation
the longitude of oruswa proves to be
not w124d09m22s
as indicated by the topozone click
but w124d09m20s29882863341

or about 119 feet east of the click point

considering the large scale of the map series used for oruswa
namely 100000k rather than the 25000k scale of the pr&vi maps
the narrowness of this error margin is quite remarkable
& shows that our careful readings should indeed fall within a few
hundred feet
or a second or 2
of the truth

end insertion
but 17 more tripoints are still to come

>
>
> but at last we do have the means to at least try for the exact

degminsecs

>
>
> so in view of the above 2 discoveries
> i immediately & excitedly tried for the 2 most difficult &

problematic of

> the 20 tripoints in this maritime category
> prusvin & prusvis
> which you may recall were last revisited in
> http://groups.yahoo.com/group/BoundaryPoint/message/12670
>
>
> now
> tho i couldnt be absolutely sure that the maps provided by

topozone actually

> included the easternmost islands of the puerto rico group &

the westernmost

> of the virgin islands group
> it does seem likely that
> http://www.topozone.com/map.asp?lat=18.3185&lon=-65.225
> shows the base points on isla culebrita for the eastwardmost

projections of

> the 3league limits of puerto rico
> namely
> cabo del pasaje for the northeastwardmost arc
> & the islet just southeast of punta del este for the

southeastwardmost

>
> & if you zoom this swatch all the way out to 1000000k
> you will see where these points are in relation to all the

easternmost

> islands of puerto rico
> including the entire culebra group & vieques etc
> & indeed in relation to the northeast coast of puerto rico itself
> as well as in relation to the westernmost of the virgin islands
>
> & you will also see the virgin passage that lies between these

2 groupings

> & where both of the tripoints will fall
> on the atlantic & caribbean sides respectively of this passage
> & actually within the area indicated in black there rather than

blue

> owing to the nonexistence of topos of the open sea
>
>
> & proceeding next into similar detail on the virgin side
> it seems similarly likely that the basepoints for the

westwardmost

> projections of the 3mile limits are
>

http://www.topozone.com/map.asp?lat=18.33778&lon=-65.0852
8

> on one hand
> for the southwesterly arc based on the islet just southeast of

virgin point

> on savana island
> &
>

http://www.topozone.com/map.asp?lat=18.40583&lon=-65.0608
3

> on the other hand
> for the northwesterly arc based on the islet just west of

cockroach island

>
> & btw you can again find your place if necessary by zooming all

the way out

> here too
>
>
> so after clicking as carefully as possible on all 4 of these

relevant base

> points to get their best available degminsecs
> i then mapped these points on graph paper & ran some trial

arcs out from

> them
> at the respective 9nm & 3nm radii
> in order to get rough positions for the 2 arc intersections
>
>
> then with the help of this great circle calculation site
> http://www.wcrl.ars.usda.gov/cec/java/lat-long.htm
> i was able to check & improve the accuracy of my intersection

projections

> thru 6 more trials in each case in fact
> until i finally reached fully coordinated positions of
> nlat 18d25m46s x wlong 65d06m35s
> or about 3nm wnw of cockroach island
> for prusvin
> &
> nlat 18d17m29s x wlong 65d03m53s
> or about 3nm actually sse of savana island
> for prusvis
>
>
> as for the best available pics
> these are only for prusvin
> & probably only class e
> http://www.vacationrentalsonline.com/vr/st/st1006/st1006.htm
> with nothing at all yet for prusvis
>
>
> but anyway
> with both of these most difficult positions finally in hand
> & with the considerable help already provided by lowell too
> it should now be comparatively easy to find & zero in on the

remaining 18

> maritime tripoints of the usa down to the same level of

accuracy

>
> then we could scarf up pix not only of but actually from all 20 of

these

> tripoints on a single continuous cruise
>
>

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