Ultra rapid vs Rapid
compare the WAAS positions against the ITRF position on the OPUS output. It is only given in XYZ or lat/long/height, not UTM, so you have to convert or do a geodetic inverse (or an ECEF inverse).
I do not know offhand the epoch date for the WAAS corrections, but I would assume it is fairly recent. Maybe they update it once a year like the broadcast ephemeris is updated?
WAAS
Sat Al wrote:
"State Plane is a coordinate system. UTM is a coordinate system.
"NAD83 is a datum. ITRF is a datum.
"You can have SPC/NAD83 coordinates and SPC/ITRF coordinates. Same SPC State/Zone/Units, but several feet apart due to the difference in datums."
I'm not so sure about that. Consider this Vermont law, which is probably typical, since NGS has put forward model legislation:
The plane coordinate values for a point on the earth's surface, used to express the horizontal position or location of such point on the Vermont Coordinate Systems, shall consist of two distances, expressed in U.S. Survey feet and decimals of a foot when using the Vermont Coordinate System 1927 and expressed in meters and decimals of a meter, or U.S. Survey feet and decimals of a foot when using the Vermont Coordinate System 1983. One of these distances, to be known as the "x-coordinate," shall give the position in an east-and-west direction; the other, to be known as the "y-coordinate," shall give the position in a north-and-south direction. These coordinates shall be made to depend upon and conform to plane rectangular coordinate values for the monumented points of the National Spatial Reference System established by the United States Coast and Geodetic Survey, its predecessor, or its successors. (Amended 1987, No. 169 (Adj. Sess.), § 2, eff. May 3, 1988; 2007, No. 164 (Adj. Sess.), § 39.)
So if the NGS never published SPC/ITRF coordinates for monuments, that approach isn't legal for the Vermont Coordinate System, is it?
WAAS
I believe it is a MISUSE of the state plane coordinate systems to use them on anything other than NAD83 or NAD27. Yes, they certainly can be used with ITRF, but to me that is very dangerous. There isn't even any change in parameters required, as GRS80 is the RECOMMENDED ellipsoid for ITRF. In actuality there is no ellipsoid for ITRF, as it is basically an ECEF system. But they do recommend GRS80 if transforming XYZ to lat/long/hgt. Of course, the WGS84 ellipsoid could be used as there is no significant difference between GRS80 and WGS84 (as far as ellipsoids are concerned).
UTM, on the other hand, has no such restrictions. It can be used with any datum. That is why metadata is so important. You cannot tell from looking at a coordinate what datum it is based on. It does, however, bother me when UTM is used with feet units. Blasphemy. But sometimes the local Corps district requests UTM feet. You would think the federal government would use the metric system, especially one that is connected to the military, but not so.
I typically send out excel spreadsheets with station data, and at the bottom I place a few lines telling what datums (H and V), SPC zone, UTM zone, feet units (if included), and geoid model were used. Nothing complicated, just the basic info to know what was used. The Corps of Engineers developed a program called CORPSMET
WAAS
I think the point was that you can project any lat/long into state plane coordinates, whether they're derived from NAD83, ITRF, or whatever. The whole reason we use the State Plane 1983 (ITRF to NAD83) coordinate system for WAAS surveys is that it aligns the data much more closely to NAD83 than straight up ITRF is.
WAAS
> I think the point was that you can project any lat/long into state plane coordinates, whether they're derived from NAD83, ITRF, or whatever. The whole reason we use the State Plane 1983 (ITRF to NAD83) coordinate system for WAAS surveys is that it aligns the data much more closely to NAD83 than straight up ITRF is.
Of course the projection can be done; the fault would be labeling the result "state plane coordinates". A better label would be "ad hoc coordinates inspired by state plane coordinates".
Ultra rapid vs Rapid
> WAAS is the opposite of "autonomous". WAAS uses corrections determined at a network of base stations (usually at FAA ATC facilities). Autonomous means "no corrections", just using the broadcast ephemeris.
Okay, a corrected Autonomous point. How's that. 🙂 It's not survey grade but ya caught the tater on that one John. 🙂
Ultra rapid vs Rapid
My here positions are typically within 6' of OPUS as well. That may be where my head was pointed prior to coffee this AM.
WAAS
I'm writing from purely a math perspective, and maybe a vendor software perspective. Certainly not a legal one.
That said, I know a lot of people who work in SPC/ITRF, and many don't know it.
WAAS has done a lot to bring this subject to light because what other source of GPS corrections uses ITRF as a reference??
You could say that WAAS is introducing confusion, but you could also argue that WAAS is way ahead of its time. What will be the standard reference frame we use ten years from now?
> Sat Al wrote:
>
> "State Plane is a coordinate system. UTM is a coordinate system.
>
> "NAD83 is a datum. ITRF is a datum.
>
> "You can have SPC/NAD83 coordinates and SPC/ITRF coordinates. Same SPC State/Zone/Units, but several feet apart due to the difference in datums."
>
> I'm not so sure about that. Consider this Vermont law, which is probably typical, since NGS has put forward model legislation:
>
> The plane coordinate values for a point on the earth's surface, used to express the horizontal position or location of such point on the Vermont Coordinate Systems, shall consist of two distances, expressed in U.S. Survey feet and decimals of a foot when using the Vermont Coordinate System 1927 and expressed in meters and decimals of a meter, or U.S. Survey feet and decimals of a foot when using the Vermont Coordinate System 1983. One of these distances, to be known as the "x-coordinate," shall give the position in an east-and-west direction; the other, to be known as the "y-coordinate," shall give the position in a north-and-south direction. These coordinates shall be made to depend upon and conform to plane rectangular coordinate values for the monumented points of the National Spatial Reference System established by the United States Coast and Geodetic Survey, its predecessor, or its successors. (Amended 1987, No. 169 (Adj. Sess.), § 2, eff. May 3, 1988; 2007, No. 164 (Adj. Sess.), § 39.)
>
> So if the NGS never published SPC/ITRF coordinates for monuments, that approach isn't legal for the Vermont Coordinate System, is it?
WAAS
I made this video about the 'WGS to NAD83' translation that is available in Carlson SurvCE:
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