MightyMoe, post: 425136, member: 700 wrote: ... maybe he would devote his own time to it ...
Yea. That.
Larry Best, post: 425112, member: 763 wrote: base9geodesy,
... Just last week I found a NOS disk at about N18-18-59 W 64-46-31, no stamped ID. The place is lousy with markers, but no good data. I guess it's a popular place to send a crew to waste time, but there's no reason to stick your neck out publishing data.
The site that is "lousy with markers" is a tidal station. The marks exist to monitor changes on the site and link to the tide gauge itself. It is normal practice at these sites to periodically run check levels amongst the markers. The fact that the disk you mention is an NOS and not an NGS disk and that it has NO stamping to me means that it was set by or for CO-OPS and perhaps they have not leveled to it and deferred stamping until they do so. This is speculation in my part.
I was happy to see the integration of data between CO-OPS and NGS but remember that they are different parts of NOAA and operate with different missions. CO-OPS surveying is in support of their tide gauge network.
As for the comments about sending crews to distant locations to "waste time" I consider that insulting.
Just talked to a FEMA rep. I think they will go ahead and approve the LOMA calling it an assumed elevation. Common sense will hopefully prevail.
SPMPLS, post: 424583, member: 11785 wrote: https://www.ngs.noaa.gov/GEOID/GEOID12B/GPSonBM12B.shtml
GEOID12B is based in VIVD09 in the US Virgin Islands. Therefore, I do not think it possible that OPUS would return an orthometric height solution referenced to anything other than VIVD09 when using 12B. It would not be possible (or valid) for NGS to compute a NAVD 88 (or NGVD 29) ortho height for that geographic location using 12B.
If GEOID12B returns VIVD09 values in VI and NAVD88 values in FL, how do they make the change. Is it at a discrete line or is it feathered. I know this may be academic since it is in the ocean but I need a mind melt for the day.
John Putnam, post: 425425, member: 1188 wrote: If GEOID12B returns VIVD09 values in VI and NAVD88 values in FL, how do they make the change. Is it at a discrete line or is it feathered. I know this may be academic since it is in the ocean but I need a mind melt for the day.
Its a ledge, near Puerto Rico.
John Putnam, post: 425425, member: 1188 wrote: If GEOID12B returns VIVD09 values in VI and NAVD88 values in FL, how do they make the change. Is it at a discrete line or is it feathered. I know this may be academic since it is in the ocean but I need a mind melt for the day.
The set a turning point on the bow of the boat in Florida; then when they get to the Virgin Islands, they transfer the elevation to land...
:liar: 😉
RADAR, post: 425437, member: 413 wrote: The set a turning point on the bow of the boat in Florida; then when they get to the Virgin Islands, they transfer the elevation to land...
:liar: 😉
PK Nail?
Spike & Washer?
😎
John Putnam, post: 425425, member: 1188 wrote: If GEOID12B returns VIVD09 values in VI and NAVD88 values in FL, how do they make the change. Is it at a discrete line or is it feathered. I know this may be academic since it is in the ocean but I need a mind melt for the day.
Those GEOID12B regions are disjoint grids. Note the images at:
https://www.ngs.noaa.gov/GEOID/GEOID12B/
and, also, the grid boundary definitions in the GEOID12B readme file.
That said, VIVD09, itself, is a local mean sea level datum; unlike NAVD88.
VIVD09 is established with 3 different tide gauges on 3 different islands.
So, one could also pose the same question for island-to-island.
GEOID12B over PR/VI is a hybrid model. The GPS-BM "corrector surface"
that sits atop the gravimetric geoid is established by least squares collocation.
As such, it will provide a smoothed (feathered) rendition from island-to-island.
I wonder whether, now that relations have warmed, data from Cuba have been added to to worldwide geoid modeling efforts? I do not know there is good quality data available but remember discussions where the absence of data over the island was mentioned as a problem.