Epoch Date, and Metadata for practical use.

[Nate The Surveyor]

One of the more interesting things that got put into the LS during my original configurations, (with Shawn Billings on the phone) was the epoch date. It was 2010. I noticed this post over on the other forum:

A guy called "Mapman" posted this:

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.
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I thought a bit about it. To be able to place an epoch date in it, automates this portion of the migration of land masses. I thought that Mapman's fairly simple explanation was good. And, would possibly be of benefit to some of the Javad Users here. So, I re posted it.
I had a general idea of what Epoch Date was doing... But this was a bit more to the point.
I guess it should be a part of the metadata I put on my surveys. ie, Epoch dates.

Any further comments would be welcomed.

I want to compile a metadata list that is good, practical, and needed, for use on my surveys.

What does your meta data list look like?

Thanks

Nate

 

[Adam]

Our board pretty much mandates our certificates to have the neccessary info in them.
I do it like this, but I don't like doing it in a certificate. We have a certificate for topo, boundary, control, gps.

 

[Shawn Billings]

I use two different types of coordinate systems: Local Grid (Low Distortion Project) and State Plane. In the Local Grid (Low Distortion Projection) surveys, the central meridian is within a few miles of the survey site (typically my local grids cover a county) and I can treat Grid and Ground distances and functionally equivalent. Bearings are grid based on this local central meridian. Rather than publishing grid coordinates, I publish the latitude and longitude. From there any surveyor with a head for geodesy can convert the latitude and longitude to any projection he likes.

When I work in State Plane, I typically will label distances in Ground from a single computed Combined Factor with Grid bearings. I label the true State Plane Coordinates. I never ever use scaled coordinates and I would not recommend ever labeling scaled coordinates. The only exception being when working on a project that has already had this type of coordinate system established (such as DOT projects).

My metadata for a local system looks something like this:
Bearings related to a local grid having an origin of North Latitude 32°23' and West Longitude of 94°52'. Convergence at POB: +00°03'22".
Distances are expressed in US Survey Feet as measured horizontally along the surface of the Earth.
Geographic Coordinates are related to NAD83, 2011 Adjustment, Epoch 2010.

My metadata for a State Plane system looks like this:
Bearings are related to the Texas Coordinate System of 1983, North Central Zone. Convergence at POB: +2°00'45".
Distances are expressed in US Survey Feet as measured horizontally along the surface of the Earth. To convert reported distances (horizontal/surface) to distances measured along the Grid for the Texas Coordinate System of 1983, North Central Zone, multiply reported distances by the project combined factor of 0.999912.
Coordinates are related to the Texas Coordinate System of 1983, North Central Zone, NAD83, 2011 Adjustment, Epoch 2010.
and sometimes I add a note about areas:
Areas are computed horizontally at the surface of the Earth.

If I'm using elevations I add:
Elevations are expressed in US Survey Feet and are related to NAVD88 based on ties to the NGS CORS network: NAD83, 2011 Adjustment, Epoch 2010, Geoid 12B.

 

[Nate The Surveyor]

Thank you, Shawn.
N