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| Subject: | RE: GISList: SUM: Convert township-range-section to coordinates |
| Date: |
12/07/2001 10:34:42 AM |
| From: |
Bryan Keith |
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Here's another attempt at summarizing my replies on this issue. Some
responses were posted to this list while others were sent only to me. With
one exception, I'll summarize what wasn't posted to this list. My question
is at end since it's been a few days since I posted it.
Bill Thoen [SMTP:bthoen@gisnet.com\ explained my problem most succinctly
since he once tried to do the same thing:
> I know what you're up against, and the answer involves some
> assumptions and a bit of geometry. The assumptions involve
> defining what YOU mean to be the "center of the NW NE
> quarter-quarter of sec 15." In real life, sections are not
> perfectly square miles: I don't believe there's a single one in
> the USA. But most are square... ish. Sometimes sections are
> truncated (like at the Colorado borders: some are even split!),
> and if there's only half a section or it's triangular (like along
> rivers) it's an open question whether there actually IS a
> particular quarter.
>
> I once wrote some software to automatically spot oil wells from
> footage calls and quarter-quarter section descriptions, and it
> handled most any PLSS or Canadian land grid cadastral systems
> (they only look similar, though.) Most sections were behaved
> well enough to use in an automated process but if a section was
> too weird, the program flagged those locations for a human or a
> special geocoding routine to handle. Plan for the
> program-crashing exceptions: there are some howlers out there!
If I ever get the data that I'm still waiting for, I'll employ a technique
similar to what Bill describe: automate the roughly square sections and
flag the others. I haven't come with anything besides human interaction to
deal with oddly shaped sections.
Craig L. Amundsen [cascade6@CascadeAppraisal.com\ sent an ArcView extension
which sounds like it will help with breaking down the squarish sections
into quarters (and quarters (and quarters)). I haven't had a chance to
look at that code yet, but I can forward it to anyone who requests. Bob
Henszey, henszey@hamilton.net wrote the script. It was based on
Polygon.MakeQtrGrids (2/19/1999) by David Dow
<Ddow@ci.bakersfield.ca.us>, if I understand correctly. It sounds like
this script will do everything that I was hoping to automate.
Dylan Keon [keon@nacse.org\ sent this URL:
http://www.geocities.com/jeremiahobrien/trs2ll.html
There's a program to get coordinates given TRS information.
Brian.Braithwaite@co.washington.wi.us suggested two books:
"Boundary Control and Legal
Principles"
by Brown or "Evidence and Procedures for Boundary Location" also by Brown
David Melton [dmelton@plexisgroup.com\ pointed out a couple websites that
have legal descriptions of section surveying:
http://www.geog.umn.edu/faculty/squires/research/pls.htm
http://www.ca.blm.gov/webmanual/id147_bm3_83.htm
That's all for now. Thank you to everyone who helped me on this one.
Bryan
Well, this isn't much of a SUM since I still don't have an answer. Perhaps
I wasn't completely clear in my initial post (included below). I had a
number of suggestions and hints including how to calculate a polygon
centroid, how convert long-lat to UTM, how to get the bounding coordinates
of a polygon (none of which I was having trouble with). However, no one
offered a technique to approximate the center of a quarter section if that
section isn't roughly square. It's really a problem of not knowing what is
meant by "northwest quarter of the northeast quarter of section 15" when
section 15 looks more like a triangle than a square. Theoretically
sections should be square, but there are many exceptions. I'm not fretting
about it too much at this point since I still don't have the data that was
supposed to make this an "urgent" problem two weeks ago. I'll post a real
summary to this list if I find out anything new.
Bryan
-----Original Message-----
From: Bryan Keith [SMTP:bryan@geomega.com\
Sent: Thursday, November 01, 2001 5:47 PM
To: 'gislist@geocomm.com'
Subject: GISList: Convert township-range-section to coordinates
Hi List,
I am expecting to receive some data (I haven't actually seen the exact
format yet) that I need to get in real coordinate space. The problem is
that data will not have coordinates, but instead will have
township-range-section (the USA public land survey system) attributes.
From there some data (most hopefully) will be broken down into quarter
section, quarter-quarter, etc. This storage format itself is not unusual.
I've seen USGS datasets with locations stored in this way. I realize that
this information cannot be converted into an exact locatio
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