Many have disappeared and a good percentage of those remaining are off limits.
Many benchmarks along highways have been lost due to widening or utility construction.
On those remote from highways, landowners are becoming more possessive of their privacy.
Most of what remains are on railroad right of ways, the majority falling within the fouling line of active tracks.
Can anyone even imagine a job not connected with railroad location, with enough time available and a budget to allow for the formal access process to a monument on RR right of way?
Paul in PA
Network GPS
> Are You Prepared To Live Without NGS Benchmarks?
Absolutely. OPUS is awesome.
I Can Live With This
From a recent OPUS-RSof 1 hour 6 minutes.
LAT: 40 40 53.68166 0.005(m) 40 40 53.71296 0.005(m)
E LON: 284 45 39.96271 0.003(m) 284 45 39.94596 0.003(m)
W LON: 75 14 20.03729 0.003(m) 75 14 20.05404 0.003(m)
EL HGT: 77.239(m) 0.022(m) 75.980(m) 0.022(m)
ORTHO HGT: 111.364(m) 0.026(m) [NAVD88 (Computed using GEOID09)]
The following three successive 58 minute OPUS-RS will do.
LAT: 40 44 45.36072 0.005(m) 40 44 45.39206 0.005(m)
E LON: 284 44 32.10010 0.004(m) 284 44 32.08331 0.004(m)
W LON: 75 15 27.89990 0.004(m) 75 15 27.91669 0.004(m)
EL HGT: 72.352(m) 0.017(m) 71.093(m) 0.017(m)
ORTHO HGT: 106.336(m) 0.041(m) [NAVD88 (Computed using GEOID03)]
LAT: 40 44 45.36065 0.005(m) 40 44 45.39199 0.005(m)
E LON: 284 44 32.09989 0.006(m) 284 44 32.08310 0.006(m)
W LON: 75 15 27.90011 0.006(m) 75 15 27.91690 0.006(m)
EL HGT: 72.348(m) 0.030(m) 71.090(m) 0.030(m)
ORTHO HGT: 106.332(m) 0.048(m) [NAVD88 (Computed using GEOID03)]
LAT: 40 44 45.36075 0.007(m) 40 44 45.39209 0.007(m)
E LON: 284 44 32.10000 0.005(m) 284 44 32.08322 0.005(m)
W LON: 75 15 27.90000 0.005(m) 75 15 27.91678 0.005(m)
EL HGT: 72.358(m) 0.020(m) 71.100(m) 0.020(m)
ORTHO HGT: 106.342(m) 0.043(m) [NAVD88 (Computed using GEOID03)]
Paul in PA
.....been happening here since 2006 when NGS ultra-decimated the database here.
Howdy,
There are area requiring this purging. Many areas do not. While the monuments were purged in S La due to subsidence issues don't they remain accessible if a user selects the option to use monuments in a subsidence area?
It is inevitable that without appropriate funding and attention to mark maintenance the benchmark network will decline into irrelevance. Of course that makes the issue of creating a tool to model differences between NAVD88 and the new GRAV-D based network moot.
There is another issue. Using GPS to derive an orthometric height requires a geoid model. The hybrid models, like GEOID09, include modeling of the relationship between NAD83 ellipsoid and NAVD88 orthometric heights at points in the NGS data base. There are large differences between heights derived from the hybrid and gravimetric models.
Cheers,
DMM
OPUS-Projects will help this situation...