I suppose the drift in the declination could account for the approximate
0.9° difference. It has been ~~ 46 years since the original survey.
However, if it was corrected for true back then, shouldn't true still be
in the same place?
bp
<part15sbs{at}gmail{dot}com>
On 11/28/2016 8:09 AM, ch...@wbmfg.com wrote:
Most surveys were done true with references from known sites.
Adjusted magnetic bearing were used for sanity checks. Using actual
magnetic bearings is a an ersatz method.
You can derive an excellent true North off of polaris if you have
decent sidereal time. It wobbles in the sky by about 1 degree but you
can use polaris tables to remove the wobble. That will give you
really really good true north and a decent latitude.
http://www.cadastral.com/cad-polr.htm
Much better than attempting a magnetic compass measurements. They are
thrown off by all kinds of local variations.
This article actually talks about using astronomical measurements to
correct magnetic measurements.
-----Original Message----- From: Bill Prince
Sent: Monday, November 28, 2016 8:50 AM
To: af@afmug.com
Subject: Re: [AFMUG] Converting vectors to a shape (.SHP) file?
It has to be true, because the declination in this area is about 16
degrees. The difference between the two results I found is a little less
than one degree.
bp
<part15sbs{at}gmail{dot}com>
On 11/28/2016 5:47 AM, Adam Moffett wrote:
Is the azimuth magnetic or absolute? If they measured it with a
compass, and if it was done a long time ago, you might need to
account for the magnetic pole drifting since the measurement was taken.
This site tells me that there's about a 1/2 degree difference between
magnetic declination today as compared to 1980: Over long distances
and several measurements it might add up.
------ Original Message ------
From: "Bill Prince" <part15...@gmail.com>
To: af@afmug.com
Sent: 11/27/2016 1:17:17 PM
Subject: Re: [AFMUG] Converting vectors to a shape (.SHP) file?
This is actually for an easement, and it's open on both ends. It
does start at the corner of a quarter section, but from there it's
just a zig-zag line. Internal coordinates are unknown.
To make it more complicated, the original coordinates are based on
the "California Coordinate System, zone III", which was derived
using NAD27. So I had to convert those CCS-zone III, to NAD27
(lat/lon), then to NAD83 (lat/lon), and then to WGS84 to get
something close to something I can use with GE.
I did convert the first vector, and it appears to be off by about
12'. Something stinks...
bp
<part15sbs{at}gmail{dot}com>
On 11/27/2016 10:01 AM, Chuck McCown wrote:
I do this on a regular basis for easement work. There is a nice
range/township/section overlay you can buy for GE so you can at
least find the section corners. Most metes and bounds use a
section corner or a quarter corner as the point of beginning. If a
parcel is complex, I actually lay it out in solidworks, my 3D
mechanical design program, that way I can just directly enter the
angle directions and distances. And the parcel almost always
closes. You could do that with any drafting program most likely.
Then I export that to an image and import the image into GE.
Stretch and rotate to fit the visible landmarks and monuments.
There will always be an error in closing unless they wind up with a
"more or less" to point of beginning. That takes all the slop out.
-----Original Message----- From: Bill Prince
Sent: Sunday, November 27, 2016 10:49 AM
To: af@afmug.com
Subject: Re: [AFMUG] Converting vectors to a shape (.SHP) file?
The vectors describe a property line, and start at a fixed WGS84
coordinate. Then it's a series of distances and azimuths from there. I
tried drawing them with GE, but there is an accumulation of small
errors. There are about 10 vectors total.
Something like starting at point lat/lon, go 700 feet azimuth 8° 27'
42", then 200 feet azimuth 27° 15' 08", and so on.
bp
<part15sbs{at}gmail{dot}com>
On 11/27/2016 9:13 AM, Chuck McCown wrote:
Is the end result displaying your vectors on GE? If so there are
ways to just import them as a text file.
I did it, don't recall how, perhaps I used some kind of app but in
the end, it was easy. I may have just drawn a line and then
reverse engineered the KMZ or KML file.
-----Original Message----- From: Bill Prince
Sent: Sunday, November 27, 2016 8:58 AM
To: Motorola III
Subject: [AFMUG] Converting vectors to a shape (.SHP) file?
I have a boundary between parcels that is described as a series of
vectors (distance & bearing) from one point. Apparently this can be
imported into Google earth as a shape file (.SHP extension). I
have been
looking for, but not finding a tool that allows me to enter the
vectors
in text, and spit out the .SHP file. Does anyone know where I
might find
this?
