Mapping Angle or Convergence Angle
JOE D HEAV
convergence angle, which was known as the "theta angle" when using the
California State Plane Coordinate System, NAD 27 must be referred to as the
"gamma angle" when using the California Coordinate System, NAD 83.
Record of Survey could not be filed until correction was made to refer to
"gamma angle".
Surveying Terms and Definitions by ACSM is as follows:
ANGLE, THETA: Lambert Conformal Conic Projection - The angle of convergence,
on the developed surface of the cone, between the central meridian and the
meridian through the point.
Shelby H. Griggs, PLS
time on his hands, and second of all he does not have a clue. I have also
run into County Surveyors that needed to have the SPC system explained every
time I turned in a map.
A county surveyor should make sure a map meets the minimum requirements and
then file same. If I have an obvious problem I would like to know, however
there is way too much personal opinion going into rejection of maps for
trivial crap.
As far as I know there is no gamma angle, having only heard the term mapping
angle, theta angle, or convergence. I find no reference to "gamma" angle in
the Land Surveyor's Act Public Resources Code relating to SPC.
I think whoever required this is out of control, and even if there is
supposed to be a gamma angle, I doubt if under CA law they could reject a
map for this reason. Of course I am not in your shoes, and I admit that I
have had to make some pretty trivial changes before just to get a map filed.
Regards,
--
Shelby H. Griggs, PLS (CA,OR,WA,ID)
OrbiTech, LLC
GPS Surveying, Consulting and Training
P.O. Box 5305
Bend, OR 97708-5305
Voice / FAX: (541) 383-2715
Mobile: (541) 912-8530
E-mail: orbi...@transport.com
JOE D HEAV wrote in message
<199809112101...@ladder03.news.aol.com>...
Jerry L. Wahl
am
stuck in the past paradigm. So initially I thought this whole thing was
ridiculous.
HOWEVER much to my chagrin when I looked this up just to see if any legit source
used the gamma "symbol". Here is the very first thing I found...
from NOAA Publication NGS NGS 5 'State Plane Coordinate System of 1983' James E.
Stem, 1989 page 18
"... The "convergence angle," often also idenfied as the "mapping angle," is this
angular difference between grid north and geodetic north. .... Convergence is
not the difference between geodeti and grid azimuths, the "projected geodetic"
azimuth is not the grid azimuth. Geodetic azimuths are symbolized as "(alpha)"
and the convergecne angle is symbolized a "(gamma)". Note the change from SPCS
27, where the symbol "(theta)" was used for convergence within Lambert
projections and "(delta-alpha)" for convergence within transverse Mercator
systems, to SPCS 83 where "(gamma)" represents convergence regardless of the
projection type."
End of quoted text
For use here I had to interpret the greek symbols shown in the documetn to what I
have place in the () brackets.
I take that document to to be a one fairly authoritive "source", but it also
seems to say that the terms convergence or mapping angle are legit. Are we
dealing with terms or 'symbology' here. The next thing to check would be CA's
NAD83 coordinate system legislation. I find: "CALIFORNIA CODES PUBLIC RESOURCES
CODE SECTION 8801-8819" is the text of the NAD83 legislation. This was found
by doing the search from this page:
I find no reference to the mapping angle or similar in that document or
subsequent and no reference to gamma in anything except in reference to radiation
or chemistry.
A lot of software probably uses the terms convergence mapping and even thetasince
they were developed at the dawn of NAD83 before the "paradigm" had changed.
Corpscon uses the term "Convergence DD(A) Angle" for example.
The terms mapping angle should suffice if if 'theta angle' is provable to be non
legit by some legal authority. The term theta is probably both be usable and
understood by most of us, but maybe new generations will be clueless. When did
NAD83 system go into
effect? Who remembers? When did NAD27 go into effect?
The only other 'source' I can suggest other than that is that when NAD83 came
out, the academic community in California was concerned that they were now at a
loss as to how to teach state plane coordinates as they didn't have projection
tables (and thus perhaps nothing to teach 'about') so I think Ira Alexander
trumped up some.. Perhaps the 'gamma' angle is also referred to in that pamplet
as well as the NGS one.
I think the only reason to have projection tables is to enslave the masses, i.e.
have some 'process' that can be 'taught' short of full projection theory, and
something they can 'be tested' and used on the LS exam. Both pretty sorryexcuses
for resurrecting manual methods in the day of computers. That is just one persons
opinion however.
- jerry CA LS
JOE D HEAV wrote:
> Looking for information or authority for requiring that the mapping angle or
> convergence angle, which was known as the "theta angle" when using the
> California State Plane Coordinate System, NAD 27 must be referred to as the
> "gamma angle" when using the California Coordinate System, NAD 83.
>
> Record of Survey could not be filed until correction was made to refer to
> "gamma angle".
>
> Surveying Terms and Definitions by ACSM is as follows:
>
> ANGLE, THETA: Lambert Conformal Conic Projection - The angle of convergence,
> on the developed surface of the cone, between the central meridian and the
> meridian through the point.
>
> joed...@aol.com
--
-----------------------------------------------------------
Jerry L. Wahl jl-...@access.digex.net
www.cadastral.com "Certainty of land location has value."
--------------------------------------
JOE D HEAV wrote:
> Looking for information or authority for requiring that the mapping angle or
> convergence angle, which was known as the "theta angle" when using the
> California State Plane Coordinate System, NAD 27 must be referred to as the
> "gamma angle" when using the California Coordinate System, NAD 83.
>
> Record of Survey could not be filed until correction was made to refer to
> "gamma angle".
>
> Surveying Terms and Definitions by ACSM is as follows:
>
> ANGLE, THETA: Lambert Conformal Conic Projection - The angle of convergence,
> on the developed surface of the cone, between the central meridian and the
> meridian through the point.
>
> joed...@aol.com
--
-----------------------------------------------------------
Jerry L. Wahl jl-...@access.digex.net
www.cadastral.com "Certainty of land location has value."
--------------------------------------
Kent McMillan
>Record of Survey could not be filed until correction was made to refer to
>"gamma angle".
Since "gamma angle" is an obscure usage, why not avoid the theta-gamma
dispute and just add a statement such as:
"Bearings shown upon this map are Grid Bearings and refer to the
[identify mapping system and zone, NAD 83] as determined by [give method].
At [identify corner] Geodetic Azimuth = Grid Azimuth + [give angle]"
This should be much more intelligible 50 years hence, anyway.
Best regards,
Kent McMillan, RPLS
Austin TX
JOEL J. JANOWSKI
I believe what you are referring to can be found in: 'A Manual on ASTRONOMIC and GRID AZIMUTH' by
R.B. Buckner, Chapter 7, Section 2 on page 87.
It's one of the best and most understandable books on the market concerning this subject!
Cheers!
nigle
!~!
Kent McMillan
>I believe what you are referring to can be found in: 'A Manual on
>ASTRONOMIC and GRID AZIMUTH' by
>R.B. Buckner, Chapter 7, Section 2 on page 87.
Out of curiosity, what exactly is the form of the note that Buckner
suggests? I didn't buy a copy of Buckner's book because it
sounded like old hat to me (for years before Buckner we used grid
azimuths derived from astro observations), but am always willing to
consider the contrary.
JIMMJAYY
early surveyors/navigators. Or where can I find that information.
Jerry L. Wahl
most easily by observing polaris at upper or lower culmination, the next method is
to observe the sun or any other celestial object's altitude at meridian transit
(local apparent noon for the sun). This is a standard part of typical Solar
transit operation. These methods require some computation and ephemeris data for
the objects. Accurate time is not needed, but close time is helpful or has to be
derived by observations also.
Longitude requires accurate time and after determining a good meridian at your
location, observation of the time of transit (passing the celestial meridian) of
one or more celestial objects.
Navigational methods I am not as familair with but I think they use an initial
estimate of position and by observing the altitude of an object (sextant) at a
specific time they can derive a :"line of position) which is has an offset from the
the assumed position and a direction. A line of position indicates your true
position is "somewhere on the line" (to the degree of accuracy of your methods).
With several objects in different areas sited, multiple lines of position can be
plotted and their intersect represents your true location.
Typically stories of old explorers (Fremont, Byrd. Lewis and Clark, etc.), include
their use of sextant observations. Of course the altitude of objects can also be
observed with other instruments such as transits and theodolites.
Search for "Celestial Navigation" on the net and you will find tons of valuable and
informative links.
- jerry
JIMMJAYY wrote:
> Can anyone describe the method of determining latitude and longitude as used by
> early surveyors/navigators. Or where can I find that information.
--
-----------------------------------------------------------
Jerry L. Wahl
Tom Craft
Tom
Jerry Wahl
>
> Isn't it easier to observe polaris at elongation?
>
> Tom
It is less time critical to observe polaris at elongation for Azimuth.
At elongation the star appears to be moving up or down and thus very
small azimuth change/unit time. For finding latitude though you want
the same situation for vertical change, thus either at the top or the
bottom of
the circle the star enscribes, that is near upper or lower culmination.
Different tasks.
- jerry
JOEL J. JANOWSKI
I believe that most of the 'old' civilizations that had a good handle on [not
necessarily LAT. and LONG. but their positions relative to the stars, sun and
'wanderers' and where then able to position 'north' or 'south' ] usually had big
rocks strung in circles that could be adjusted year after year so eventually the
sun would come up between certain ones once a year, certain stars would appear over
others at regular intervals, and everything that we take as read now as being
created by 'aliens' nothing more than bound determination to get the thing right!
Personally I don't have the time to readjust Stonehenge, or recalibrate Inca
pyramids, I can barely keep good time with my 9" sun dial out in the back yard.
Latitude and Longitude as we know it today is I believe a calculated result of all
these celestial sightings at Greenwich and our understanding of time in relation to
Greenwich [pronounce Green-witch by a person in my class to the amusement of the
rest of us.]
Because of the need of 'spices' and the quest of the Europeans to 'get their
first' [yes 'their'] LAT. and LONG. as we know it were created so the ships sent
out would not fall off the turtles back! The Ancients didn't understand LAT. and
LONG. but they did understand the movement of the stars.
Now if you have a sextant and a sand hour glass or one of those new finagled
wind-up clocks, we can type!
Cheers!
nigle
!~!
JIMMJAYY wrote:
> Guys, I hate to stubborn. Originally, I asked for the old timers way of
> obtaining lat/long. Meaning 1400 AD or so. Just curious how they did it
> without all this technology.
> It is best to observe Polsaris at elongation or so I have been told.
>
> Back to the lat/long. NOVA on Educational TV is supposed to have something on
> early navigation in the near future. Be my luck to miss it.
>
> Jim P
JIMMJAYY
Jerry Wahl
century meant by your term "as used by early surveyors/navigators" ..
Before sextants came octants and quadrants and astralabs going back 1500
AD. Before accurate time, bad time hour glasses, etc. or dead reckoning
had to suffice.
-> Guys, I hate to stubborn. Originally, I asked for the old timers way of
-> obtaining lat/long. Meaning 1400 AD or so. Just curious how they did it
-> without all this technology.
-> It is best to observe Polsaris at elongation or so I have been told.
-> Back to the lat/long. NOVA on Educational TV is supposed to have something on
-> early navigation in the near future. Be my luck to miss it.
-> Jim P
Tom Werry
>Can anyone describe the method of determining latitude and longitude as used by
>early surveyors/navigators. Or where can I find that information.
FWIW, here's my bit:
I don't know about surveyors, but in the South Pacific centuries ago
(as today?) there was not a lot of land to survey, but navigation
across vast spaces of ocean was definitely a problem.
Navigators of olde used to learn to recognize subtle differences in
reflected wave patterns coming off islands & reefs hundreds of miles
away, and determine their distance & direction that way. It was
apparently easier in oceans with fewer islands than with many.
They would feel for the minute vibrations in the sea through the hulls
of their large wooden canoes by using their most sensitive body organs
- their testicles. No kidding! These old guys would squat in the
boats and rest their nuts on the deck and feel their way around the
oceans. Maybe having big cojones had a different connotation wit dese
bruddas.
I think I read this in Michener's South Pacific, But I'm not sure.
Michener always hired armies of researchers for those epic novels he
"wrote", so if you have a credibility problem with this navigation
method, ask him, not me.
I guess that's why they always had patriarchal societies in those
islands. No nuts, no navigators. Lack of navigation capability could
wipe out whole population when climatic shifts required migration.
I can forsee some potential problems:
Guys with only one ball had no depth perception?
Two of different sizes meant you went round in circles?
Undescended testicles limited your travels?
To keep you at home the wifey would get out the kitchen knife?
Foghorns are usually deep-pitched?
This is getting stupid!
Regards,Tom Werry gpsnav at pacific dot net dot sg
Programmer's Logic: Press ENTER to exit. (laugh now, here)
Joe Noonan
JIMMJAYY wrote:
> Guys, I hate to stubborn. Originally, I asked for the old timers way of
> obtaining lat/long. Meaning 1400 AD or so. Just curious how they did it
> without all this technology.
> It is best to observe Polsaris at elongation or so I have been told.
>
> Back to the lat/long. NOVA on Educational TV is supposed to have something on
> early navigation in the near future. Be my luck to miss it.
>
> Jim P
You did not need lat/long in 1400 AD; the world was flat.
mar...@gte.net
I will pass this on to my non-connected (to the internet) buddies
Mark
SamSurveyr
Good one Joe......lol.
Sam
David Ferguson
save one of them, would you have lunch or go to a movie?
David Ferguson
Columbia, SC