|
|
|
|
|||||
|
||||||
From: Ron Rogers (no email)
Date: Thu May 19 2005 - 19:49:31 EDT
Marin,
What you are saying is correct. The datum was adjusted to locate objects
more accurately and this was done worldwide for a simple reason. ICBM's
departing from one known location have to be able to accurately strike a
known location on another continent. This requires a uniform grid using the
vast array of technical resources available to the defense/intelligence
community.
Once this was done, then the GPS location of important objects was fixed on
the new grid or datum. For example, the Washington Monument's location moved
100 feet East.
We used to look for accuracy and up to date information from
photoreconnaissance and ground surveys where possible - that has changed.
Now we have an accurate grid upon which we can locate terrain features and
manmade objects with GPS where necessary.
Ron Rogers
----- Original Message -----
From: "Faure, Marin" <>
|
| I may very well have mis-interpreted the stuff I've read about WGS84,
| but so far as I can tell, it was not created using GPS. It is the
| mapping standard that's used by GPS, but the impression I've gotten is
| that it was created using other sources of data. To quote one
| description of the creation of WGS84, "...the means for producing a new
| WGS [WGS84] were available in the form of improved data, increased data
| coverage, new data types and improved techniques. GRS80 parameters
| together with available Doppler, satellite laser ranging and VLBI
| observations constituted significant new information. Also, an
| outstanding new source of data had become available from satellite radar
| altimetry. Also available was an advanced least squares method called
| collocation which allowed for a consistent combination solution from
| different types of measurements all relative to the Earth's gravity
| field, i.e. geoid, gravity anomalies, deflections, dynamic Doppler,
| etc."
|
| So it would seem that while satellite-derived data was used to create
| WGS84, GPS wasn't part of the formula. So this could imply that a chart
| that was originally based on survey data could be upgraded to WGS84
| without the use of any GPS-derived data.
_______________________________________________
http://lists.samurai.com/mailman/listinfo/trawlers-and-trawlering
To unsubscribe send email to
with the word
UNSUBSCRIBE and nothing else in the subject or body of the message.
Trawlers & Trawlering and T&T are trademarks of Water World
Productions. Unauthorized use is prohibited.
|