All I had is that I don't consider the coordinates of the subject LPD large. I answered many a call when I supported our 14 LDPs where the first thing mentioned was your LDP coordinates are in the ocean. It made for short calls as I immediately new they had chosen the wrong system. Our largest easting was in the 24 millions. A quote from our handbook: "It is strongly recommended that the coordinate values everywhere in the design area be distinct from other coordinate system values for that area (such as State Plane or UTM) in order to reduce the risk of confusing the LDP with other systems."
I tried to find a suitable old publication to figure out the answer before NAD 83 came along. At the NGS publications page I found a publication 62-3 of the US Coast and Geodetic Survey from 1968, State Plane Coordinates by Automatic Data Processing. It says on page 1
The plane coordinates in all the projections. except the one used
for Guam. are in U.S. Survey Feet (one U.S. Survey Foot equals 1200/3937
meter exactly).
Your post broke the thread because the links you used have some weird code prepended to the URL you are trying to use. It looks like some sort of Chrome extension is causing it. The only way to fix it was to hunt down this thread in the database and manually remove the weird code. 🙂
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This NGS Special Publication is pretty comprehensive on all things SPC:
https://geodesy.noaa.gov/library/pdfs/NOAA_SP_NOS_NGS_0013_v01_2018-03-06.pdf
I have an add-on package for Bricscad that does coordinate systems and projections. It is using EPSG 30248 for Washington State North Zone and EPSG 30249 for WA South Zone. Those seem to be specified as International Feet, and I am wondering, is that really so? If I use these to convert some old NAD27 section breakdowns to NAD83/2010 they wind up out in left field because of the large coordinate numbers and the difference between the kinds of feet.
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If that's true about the unit of measure, Bricscad had the definitions wrong. EPSG registry uses US survey feet for 30248 and 30249. Here's a link to 30249. Look at the "coordinate system" section.
@mathteacher "The international foot was defined in 1959" ... And, so was the US Survey Foot!
Yes, prior to 1959, there was only one conversion from meters to feet in the US. That was 1 foot = 1200/3937, which has been called the US Survey Foot since 1959.
So, when we look back to measurements made prior to 1959, they "all" used 1200/3937 to convert meters to feet. Hence, they were all US Survey Feet. Nobody knew that when the measurements were made, though, because the term US Survey Feet had not been coined.
The "all" in quotes recognizes that many different conversion factors have been used, so there are some odd ones out there. Clarke was not always consistent with his meters; undoubtedly there are other examples as well.
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ALL NAD27 coordinates and ALL elevations both NGVD29 and NAVD88 when expressed in feet used US Survey Feet at least on NGS datasheets. With NAD83 the units for feet were state by state, some US Survey Feet, some International Feet and I believe a few unspecified which I think were assumed to be US Survey Feet.
SHG
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The state's legislation determines it. Some states did not determine which to use, why I will never understand.
@bill93?ÿ
I don't know, Bill. that extra 1/4" can make a hike VERY arduous when hiking in the Pecos Wilderness (or it may have something to do with the fact that I live at +/- 122' above MSL).
@bill93 We are talking GPS, your horizontal position affects your location on the derived Geiod model, the overall question is intriguing as to whether or not there is additional distortion in the verticals as a result of conversions.?ÿ
Of course get in NAD83 before looking at the geoid. But try comparing the geoid at a location near you versus a couple hundred feet away. In most places the difference is insignificant.
What if the NGS adopts a 2027 datum? Might we call it the NAD 27? Just when you think it can't get more confusing.....
Of course get in NAD83 before looking at the geoid. But try comparing the geoid at a location near you versus a couple hundred feet away. In most places the difference is insignificant.
Very true. The GEOID18 grid cells are 1 arc-minute in size, which translates very roughly to 5000 x 5000 feet. When interpolating a few centimeters across those distances, change doesn't usually happen very fast.