So you leave off the SPC and keep it as private information in you own files?
Larry Best, post: 391067, member: 763 wrote: So you leave off the SPC and keep it as private information in you own files?
Most boundaries have no State coordinates shown anywhere, I would advise not using coordinates for boundaries since they are just a snapshot in time anyway, so the metadata if it's on a state coordinate system should state it the way your state law describes.
I think most states have a requested format. And you are only stating metadata for bearings and distances. I would look up the state format and use it, it will probably read something like "bearings are based on the XYZ Coordinate System, NAD 1983, East Zone". Then you need to state what kinda distances if they are state plane just say "bearings and distances are.......
If they are surface then state that and what factor is used to get from state plane to surface distances.
For this the EPOCH and such are completely irrelevant because NAD83 (1986) and NAD83 (2011) will be the same on the ground between two points with regard to bearings and distances.
If you are doing engineering drawings or are required to give coordinates then you need more metadata including the EPOCH, the source of elevations, and I would include the CORS or the HARN points that create the data.
I would also include the NE or LL of those points and the GEOID model used. All that is important, I usually create a list of control points and the cors points and bench marks relevant to the project, I have never mentioned anything about OPUS in a metadata statement (at least I cant recall ever doing it).........
MightyMoe, post: 391071, member: 700 wrote: For this the EPOCH and such are completely irrelevant because NAD83 (1986) and NAD83 (2011) will be the same on the ground between two points with regard to bearings and distances.
It's true the bearings and distances will match. But any time you state NAD83 you should go ahead and give the datum tag NAD83(xxxx). What's it hurt? And the next guy doesn't have to guess if he makes any use of your coordinates.
Bill93, post: 392558, member: 87 wrote: It's true the bearings and distances will match. But any time you state NAD83 you should go ahead and give the datum tag NAD83(xxxx). What's it hurt? And the next guy doesn't have to guess if he makes any use of your coordinates.
It's extremely rare to see coordinates on a survey, most boundaries and descriptions make no reference to any coordinates, so there is no point to the EPOCH; it doesn't hurt, but it doesn't accomplish anything without coordinates.
Now if you do give out coordinates then the EPOCH is just a start for what should follow, but yes the EPOCH is important IF you are giving out coordinates, but my guess is that 90% or greater of surveys have no coordinates displayed or referenced.
Coordinates and meta data on boundary maps are usually covered by Statute. Here they are still considered supplementary if used in a description. It will take them a long time to go any higher in the order of calls in these parts. I'm fine with that...
When I come across any coordinates on a survey, I usually plot them with which ever coordinate system that's specified. My software doesn't care what epoch it is. I then go find the object that the coordinates were given for and tie them into my survey. Am I missing something more important?
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My point is that I have information that may be useful evidence for reestablishing my survey in the future. Why shouldn't I put it on the drawing?
arctan(x), post: 392623, member: 6795 wrote: When I come across any coordinates on a survey, I usually plot them with which ever coordinate system that's specified. My software doesn't care what epoch it is. I then go find the object that the coordinates were given for and tie them into my survey. Am I missing something more important?
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I think you are acting rationally.
To expect coordinates to be exactly pinpointed on a monument will be a frustrating experience.
But if I do publish coordinates I do explain what EPOCH and basis they came from.
Getting a plan set that says SPC xxx with no EPOCH, no control, no monuments is happening more often.
MightyMoe, post: 392669, member: 700 wrote: I think you are acting rationally.
To expect coordinates to be exactly pinpointed on a monument will be a frustrating experience.
But if I do publish coordinates I do explain what EPOCH and basis they came from.
Getting a plan set that says SPC xxx with no EPOCH, no control, no monuments is happening more often.
So what use is it to give details on the epoch?
How does that help anyone locate the coordinates? I'm not trying to be argumentative, I just need some education on the subject.
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arctan(x), post: 392730, member: 6795 wrote: So what use is it to give details on the epoch?
How does that help anyone locate the coordinates?
It makes it possible in the future to transform the coordinates into values that more nearly reflect those at the future epoch. In Texas, the horizontal components of NAD83 velocities of most stations are not huge, but fast forward fifteen or twenty years and future surveyors will thank you. Adding the Epoch tag to NAD83 coordinates costs basically nothing and is worth more than just something.
In an area with lots of nearby CORS sites, the simplest transformation will usually be as a translation using the published values of the CORS antenna at different epochs. That should be simple to do as long as the NGS Database is accessible and NGS is updating the coordinates of CORS sites at different epochs.
Bill93, post: 392558, member: 87 wrote: It's true the bearings and distances will match. But any time you state NAD83 you should go ahead and give the datum tag NAD83(xxxx). What's it hurt? And the next guy doesn't have to guess if he makes any use of your coordinates.
And, more to the point, the future surveyors will tend to assume that anyone who reported NAD83 coordinates without noting the Epoch of the same was probably didn't know what he or she was doing. So, if you're actually doing a diligent job, you want to leave a record that is consistent with that fact.
I'm sure that other surveyors aside from myself look at records of prior surveys from the near-term past and estimate the competence level of the effort from the little things like the Bearing Basis note and some statement as to how coordinates were derived.
What Kent said is spot on.
Add a listing of control monument values used and you have recoverablity.
Working on the West coast, we learned epochs change, lots.
Most of the US is much less, but it still matters.
So in the future, what is the method for determining the epoch? Is that given in the OPUS report?
What would be the procedure/work flow for retracing a survey made in a certain epoch? What makes the epoch so important?
This is the kind of material that should be covered by some continuing education course.
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arctan(x), post: 392758, member: 6795 wrote: So in the future, what is the method for determining the epoch? Is that given in the OPUS report?
What would be the procedure/work flow for retracing a survey made in a certain epoch?
Yes, OPUS will report a position with respect to NAD83 at some standard Epoch. There are different ways of updating coordinates from some prior standard Epoch, but in my view the most practical one (in Texas) is simply to examine the data sheets of the nearest CORS sites and, by simple arithmetic calculate the shifts necessary to to translate coordinates at one Epoch to another.
Where the CORS sites are more distant, one could use the HTDP software since it also takes into account any (very small) rotations from Epoch to Epoch.
this might help http://www.sdi-baja.com/survey/EpochConversions.pdf
I provided this to the staff back in 2006, but there is probably an easier way
Peter Ehlert, post: 392796, member: 60 wrote: this might help http://www.sdi-baja.com/survey/EpochConversions.pdf
I provided this to the staff back in 2006, but there is probably an easier way
Good intro. The HDTP program is slightly different from 2006 I think. Here is a newer result.
HTDP (VERSION v3.2.5 ) OUTPUT
UPDATED POSITIONS IN NAD_83(2011/CORS96/2007)
FROM 5-08-1991 TO 1-01-2007 (month-day-year)
FROM 1991.350 TO 2007.000 (decimal years)
OLD COORDINATE NEW COORDINATE VELOCITY DISPLACEMENT
LATITUDE 33 40 18.87000 N 33 40 18.88498 N 28.20 mm/yr 0.462 m north
LONGITUDE 117 50 24.00000 W 117 50 24.01484 W -24.62 mm/yr -0.382 m east
ELLIP. HT. 25.000 24.984 -1.22 mm/yr -0.016 m up
X -2481446.101 -2481446.314 -14.00 mm/yr -0.212 m
Y -4698527.510 -4698527.094 26.22 mm/yr 0.416 m
Z 3516232.206 3516232.581 22.79 mm/yr 0.376 m
The displacement is the result needed. It shows the estimated amount of shift from one date to another. This can be directly applied to the "original" coordinates to bring them into this epoch or whatever epoch you need. In this example you get an idea of how much it actually moves over time.
good example of how things move https://surveyorconnect.com/community/members/mapman.6096/&apos ;">Mapman
remember, the conversion is an approximation, and will differ from a true adjustment ... back in the day there were not all that many monuments available so we had to futz around to get tied to control that was kinda reliable.
But if that what you are doing (epoch conversion), document it in your map/report/description so that our grand kids can figure out what we did.
Thanks Mr Mapman. I quoted your post above over on the Javad Forum. I felt it was nice and concise, and made it easy to wrap my mind around the basic concepts.
What is your practical metadata list, to go on surveys? Ie, the "Rest of it". I'm now including the Epoch date, on my work. Javad has a setting in their units, that allows you to SET the epoch date... which automates this... Your explanation brought this to mind, and makes me want to get ALL the necessary metadata in a row....
Thanks again. Hope you did not mind me copying and pasting it.
Nate
I have found these handy:
ALT + 237 Gives me THETA in Carlson/Acad.
ALT + 241 Gives the + - together.
ALT + 248 Gives me the degree symbol å¡
Thanks
N