New Data Sheet Format
October 1, 2007
Background
On February
9, 2007, the National Geodetic Survey (NGS) completed a readjustment of more
than 70,000 GPS survey control stations in the National Spatial Reference
System. This adjustment included
stations in the conterminous United States, Alaska, Puerto Rico and the Virgin
Islands. The adjustment was performed to
(1) fulfill a requirement stated in the Federal Geographic Data Committee
(FGDC) Draft Geospatial Positioning Accuracy Standards (FGDC 1998) to develop individual
local and network accuracy estimates for each point in the network, and (2) to
resolve inconsistencies between the existing state-wide High Accuracy Reference
Network (HARN) adjustments, the nationwide network of Continuously Operating
Reference Stations (CORS) as well as between states.
Throughout
the year NGS has presented the results of the National Readjustment and
discussed the pending data sheet changes.
At this time, the readjustment has been loaded into the NGS integrated
database and data sheet changes will be implemented over the next 30 days to
minimize the impact on users.
Impact
Thursday, November 15th, 2007
Data sheet modifications for the NAD 83 (2007) coordinates
The following modifications to the data sheets have been implemented:
- Upon further consideration, NGS has decided not to implement the "NAD 83(NSRS2007)" datum tag on datasheets, and will maintain the "NAD 83(2007)" tag as the permanent identifier of points that have an NSRS2007 coordinate.
- The format of the records for the NAD 83 latitude and longitude and the NAVD 88 Helmert orthometric height have been permanently changed to keep the same spacing as the previous data sheet. The inclusion of 'NSRS' in the datum tag had moved both fields to the right five places and caused applications which take data sheets as input to fail. The new, permanent datum tag will now read NAD 83 (2007) and an explanatory note will be added to the data sheet to explain that the datum tag '2007' means 'NSRS2007'.
- For survey control stations determined 'NO CHECK' by the national readjustment, the published NAD83 coordinate line has been designated 'NO CHECK' (replacing 'ADJUSTED') and the ELLIP HEIGHT line has been designated 'NO CHECK' (replacing 'GPS OBS').
- The ellipsoid height line has been designated 'ADJUSTED' rather than 'GPS OBS' (except for NO CHECK stations; see above).
- After further review and analysis NGS decided to leave the Network Accuracies on the data sheet. The Local Accuracies will not be published on the data sheets at this time. NGS is working to update the output format of the Local Accuracies. In the interim, the Local Accuracies are available in Re-adjustment Distribution Format (or “RDF”).
The previous update notice for the data sheet may be found here.