From: "Randall" <tr3driver@ca.rr.com>
> > USGS sea level reading - 694.10 = Saint Paul City Datum
>
> Phil, are you sure that's Mean Sea Level ? Sounds to me more like an
> ellipsoidal height (meaning the theoretical model of the entire earth's
> surface that datums like WGS-84 are based on). There are of course, some
> places that are below MSL, but even Death Valley is only 282 feet below.
Randall, I don't know whether you haven't been following the bread crumbs or if
you are trolling. Just to play along, I'll pretend you are serious.
Saint Paul is above sea level. This makes a lot of sense because the
Mississippi River flows downhill. The magical mythical point on the
Mississippi upon which early surveyors decided is now known to be 694.10 feet
above USGS sea level. Therefore, 694.10 USGS is equal to zero Saint Paul City
Datum. Therefore, a USGS elevation minus 694.10 equals a Saint Paul City Datum
elevation.
> > Sometimes a surveyor will not call for benchmarks and just pick a random
> > place on the site and call it "100.00".
>
> Which of course is the same basic process that produced your "Saint Paul
> City" datum.
> <G>
Yes, but the early surveyors had no choice. The point they chose remained
consistent over the entire period of the city's development. Now that more
accurate methods are available, we have a number to convert our local standard
(used on 10,000 sewer maps) to a national standard.
This is not comparable to today's surveyor choosing a random point on a single
building site. Today's surveyor has an easy process to create a site plan
showing elevations directly tied to either the national standard, the local
standard, or both. To create a site plan with no reference to either standard
seems like sub-standard work to me. Without a reference to existing
benchmarks, a builder would have to go out to the site and shoot some
elevations again to relate his site plan to existing City records of sewer
elevations.
--
Phil Ethier West Side Saint Paul Minnesota USA
1962 Triumph TR4 CT2846L, 1992 Saturn SL2, 1993 Suburban,
1994 Miata C package
pethier [at] comcast [dot] net http://forum.mnautox.com/forums/
http://www.flickr.com/photos/pethier
I decry the textmessagization of the American-English language.
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