TMG-L ArchivesArchiver > TMG > 2011-02 > 1297777884
From: "Darrell A. Martin" <>
Subject: Re: [TMG] Giving locations by UTM
Date: Tue, 15 Feb 2011 07:51:24 -0600
On 2/15/2011 12:53 AM, Dennis Lee Bieber wrote:
> On or about 2/14/2011 10:07 AM a carrier pigeon from Darrell A.
> Martin delivered:
>> The GPS gets me close. The landmarks, a
>> small compass, and a cloth tape measure nail it down. If the combination
>> doesn't find it, either I have gone blind or it "jist ain't there".
> Pity TMG is not rigged for UTM coordinates...
> UTM coordinates ARE in meters, and if you aren't taking too
> long (meaning the Navstar satellite configuration changes
> noticeable), taking the difference of the UTM easting and northing
> for the landmark item and the subject item would give you the direct
> meter measure...
I have gotten into some of the finer points regarding UTM recently. I
would not recommend it for genealogists. We can discuss decimal degrees
versus degrees, minutes, and seconds, and TMG's precision or lack
thereof, but the choice of the latitude and longitude system itself is
unassailable. It makes sense because of its universality, its longevity,
and the existence of a readily available and affordable tool, GPS, which
uses it. There is no comparable tool for UTM.
Those who are not obsessed with maps, mapmaking, and finding small
things on the surface of the earth may happily stop here. Detailed
blathering after a short pause.
I have more or less successfully turned a 1969 epoch UTM 1:50,000 map,
bilingual English/Vietnamese, into a tool that former members of my Army
unit can use for two things: to make sense of old photos, and to pin
down the locations of buildings on Tay Ninh West Base Camp. It both
helped, and confused, to find that the main "streets", the airstrip, and
the outline of the base camp all show up on Google satellite pictures
even today, 4 decades later, with a great deal of clarity. Google Earth
places the location of the Orderly Room of the 228th S&S Co (DS) as follows:
11.324295 deg. N, 106.057569 deg. E
- or -
11 deg 19 min 27.46 sec N, 106 deg 3 min 23.12 sec E
- or -
48 P 615410.86m E, 1252046.49m N (UTM)
- or -
G.E. also offers the equivalent in degrees and decimal minutes, in case
you wondered. Note also that all these are given with centimeter
precision (which I find dubious). So, TMG would not be able to store
this location accurately even when it is provided in its chosen storage
format, because G.E. takes the seconds to two decimal places. TMG uses
Anyway, we old veterans discussed how we were going to communicate
precise locations. We rejected UTM as not widely enough understood, even
though the only useful map we have is UTM. I eventually proposed an
idiosyncratic system of "blocks" based on the right-angle street grid on
the base camp, which everybody liked. (Even though the engineers had
"helpfully" rotated the street grid about 20 degrees from true N-S/E-W.
Finding something the size of a gravestone using UTM would have just as
many difficulties as true lat/long coordinates. Not better or worse,
though; the issues would just be different.
The first problem (which John Cardinal alluded to) is that the systems
of lat/long and UTM are not directly convertible. While UTM provides
direct meter measurements to the precision of the map, it is
directionally imprecise. In our case, moving among magnetic, UTM grid,
and "true" compass directions didn't matter enough to cause problems. We
were dealing with an airstrip 1.3 km long, million-gallon fuel storage
tanks, and a couple buildings the size of football fields. The landmark
to end all landmarks was Nui Ba Den, the "Black Virgin Mountain".
The second concern, and the biggest one in the long run, is the
longevity of the UTM system. According to <http://www.historyworld.net>
"the grid system of latitude and longitude dates back to Hipparchus in
the 2nd century BC, and the prime meridian (or 0 degrees longitude) has
run through the Canaries since the second century AD, placed there by
Ptolemy." Printed maps using this system started being readily available
in the 16th Century. GPS uses lat/long.
The UTM system was invented very recently, by the US Army Corps of
Engineers in the 1940s. Because it preserves distances precisely, it is
very useful for, say, directing artillery fire....
For more than any reasonably sane genealogist would probably want to
know about UTM, check out:
|Re: [TMG] Giving locations by UTM by "Darrell A. Martin" <>|