FREQUENTLY ASKED QUESTIONS
When will the new adjustment be finished?
The master plan has initiation of the first layer of the adjustment in
June 2005, and completion of the airport layer in October 2006. The
regional layers will be adjusted from November 2006 through September
2007.
Could it be completed sooner?
The upper layers proceed sequentially and require set amounts of
analysis. The regional layers could be processed simultaneously. It is
conceivable that if additional personnel were available, the regional
layers could be completed no sooner than April 2007.
When will I see new coordinates in my area?
One will immediately see some new coordinates when National Layer 1 is
completed in December 2005. The NGS Integrated Data Base will be
updated as each layer is completed. In the event of software
development delays, statewide contingency adjustments (without
accuracies) will be initiated to insure updated coordinates are
delivered as soon as possible to our users.
When will I know if the contingency adjustment is executed for my area?
The National Readjustment Web Page will contain a link showing if the
contingency adjustments have begun, and the current
contingency schedule.
When will I see these new network and local accuracies?
One will begin to see these fields populated in our data sheets at the
same time the new coordinates also appear -- for example, National Layer
1 will be completed in December 2005, and the last region will be
completed in September 2007. However, if contingency adjustments are
performed, these will not provide the new accuracy values.
What is the deadline for submission of a GPS UDN project for the
readjustment?
The National Readjustment Web Page will contain a link showing the
current schedule for the regional
layers, which will be initiated November 2006 through August 2007. In
general, UDN projects must be submitted at least 6 weeks prior to the start
of a given region to allow for review and possible reprocessing.
What about classical horizontal control surveys?
The Readjustment of the NSRS will contain only GPS projects. At the completion
of the project, datum transformation grids will be developed to support
those legacy data.
Will the currently published coordinates for the classical triangulation
network stations still be available to the public?
NGS has no intention of "abandoning" the classical triangulation network
stations. These stations will still be published as part of the National
Spatial Reference System; they just will not participate in The Readjustment
of the NSRS. When you look at the level of distortion that is anticipated to
be removed by this adjustment, it's on the order of 3-7 cm. That's in the
noise of the positional uncertainty of the classical network, which in most
cases is good to 10-40 cm. The transformation algorithm will allow us to
model the positions of the classical network to fit more closely with the GPS
data.
What happens afterwards?
First, a report on the project will be written in October 2007 through
December 2007. Then work will proceed on building datum transformation
grids (horizontal and vertical) between the newer and older
coordinates. Plans will be developed and executed for adjustment of
Hawaiian and Alaskan GPS networks. We continue reference frame
maintenance work for both NAD 83 and ITRF coordinate sets. And, of
course, we will be training our users on the network and local
accuracies.
Why not abandon NAD 83 and use ITRF instead?
The legislation of many states specifies NAD 83. A burden would be
imposed on the states if they were requested to change their laws.
Instead, final coordinates will be published in both the NAD 83 and ITRF
reference frames. By maintaining both reference frames, the greatest
number of users will be served.
What are local and network accuracies?
A local accuracy of a control point is a value that represents the uncertainty
of its coordinates relative to other directly connected, adjacent points at the
95-percent confidence level. It will be an approximate average of the
individual local accuracy values between this control point and other observed
control points used to establish its coordinates. A network accuracy of a
control point is a value that represents the uncertainty of its coordinates
with respect to the geodetic datum at the 95-percent confidence level. The
datum is considered to be best expressed by the Continuously Operating
Reference Stations (CORS). A more detailed explanation can be found in the
following FGCD document:
