Tuesday, September 4, 2012
GEOID12A Model Nearly Finalized
The National Geodetic Survey (NGS) has modified the GEOID12A model on the NGS Beta website. After further analysis of the existing control data, we have modified several additional control points in Alabama, as well as a few points in Wisconsin. NGS expects these points to be the final changes, however the GEOID12A model will continue to be posted on the NGS Beta website until around September 10 for any final comments, after which time we expect to release the model for production.
Following the initial release of GEOID12, several suspect control points were identified and corrected. Click here for a link to those corrections. A first iteration of the GEOID12A model (version 1) was developed from the corrected control data and was released with a notice outlining those changes.
Subsequent analysis has determined several additional suspect points in Alabama and Wisconsin. These points were corrected, and GEOID12A (version 2) is now available on the Beta website. The table, below, summarizes the changes.
|
|
|
GEOID12A (v. 1) |
|
GEOID12A (v. 2) |
|
||||
|
PID |
ST |
EH (m) |
OH (m) |
Reject? |
Change |
EH (m) |
OH (m) |
Reject? |
Comments |
|
|
|
|
|
|
|
|
|
|
|
|
BH3164 |
AL |
-13.221 |
15.279 |
No |
Reject |
-13.221 |
15.279 |
Yes |
VTDP/AL req |
|
BH3165 |
AL |
-14.151 |
14.339 |
No |
Reject |
-14.151 |
14.339 |
Yes |
VTDP/AL req |
|
DL7331 |
AL |
*** |
*** |
*** |
New Point |
4.461 |
32.259 |
No |
Missed CORS site |
|
DM5373 |
AL |
238.544 |
263.305 |
Yes |
OT: 4.5 m |
238.544 |
267.625 |
No |
Change OT |
|
DM2662 |
AL |
158.085 |
184.714 |
No |
Keep as is |
158.085 |
184.714 |
No |
Keep – reject below |
|
EF0792 |
AL |
148.544 |
175.250 |
No |
Reject |
148.544 |
175.220 |
Yes |
Near DM2662 |
|
NG0372 |
WI |
161.637 |
196.386 |
No |
OT: 0.024 |
161.637 |
196.410 |
No |
Incorrect OT loaded |
|
NH0083 |
WI |
259.555 |
293.637 |
No |
OT: 0.032 |
259.555 |
293.669 |
No |
Incorrect OT loaded |
|
PM0119 |
WI |
162.024 |
198.146 |
No |
OT: 0.047 |
162.024 |
198.193 |
No |
Incorrect OT loaded |
|
PO0408 |
WI |
173.401 |
203.859 |
No |
OT: 0.007 |
173.401 |
203.866 |
No |
Incorrect OT loaded |
The image, below, displays the impact of the changes between version 1 and version 2 of GEOID12A. The impacts are a few centimeters localized at the points shown in the table.
Impact of corrections between version 1 (August 11) and version 2 (August 31) of GEOID12A.
GEOID12A version 2 will remain on the NGS Beta website until around September 10, 2012, to allow for final analysis. Assuming no further changes, GEOID12A version 2 on the Beta website will become the final version of GEOID12A and will be released, simply as GEOID12A, on the NGS public website and on NGS Datasheets. At that time, GEOID12A will also be available for production work, including new Height Modernization surveys and other GPS projects referenced to the NAD 83(2011) epoch 2010.00 realization.
This process has been a complicated one, and NGS would like to express our thanks to all those who have contributed to our moving forward and developing a much-improved product. We look forward to using a similar process for the release of future geoid model products to better ensure the integrity of control data used in model development.
