My predecessor here (who is unreachable) provided the horizontal and vertical control for a 2,000 acre parcel we had flown in 1998. He provided this statement to the photogrammetrists: "the horizontal datum is NAD83 NY east zone raised to local using a factor of 0.9999. The vertical datum is NAVD88."
When I and another surveying company now occupy some of the original control points using RTN, the horizontal differs by about 138' (vertical is off a few tenths) from those datums.
I don't know how he established his control-paper trail is scarce. We do have a couple of Trimble 4600LS's in the closet. Were they around in '98?
Some other parcels he supplied control for I've checked into under a tenth both vertically and horizontally, but another is 5' off, both H & V. (another may be on NAD27 but that's another story).
Any idea what may have happened here?
its funny, we typically match others survey coordinates within a tenth or they are way off.
In talking with one of the guys where the info was way off, it turns out that they held scaled info from a quad map and that was fairly common with some guys.
When you really know their info is wrong is when we bring in the Ortho overlay images and they fall where they should with our stuff and the other guys stuff is about a hundred feet away and on the wrong side of the road!
May have the same situation on your job
muncle56, post: 430635, member: 8893 wrote: My predecessor here (who is unreachable) provided the horizontal and vertical control for a 2,000 acre parcel we had flown in 1998. He provided this statement to the photogrammetrists: "the horizontal datum is NAD83 NY east zone raised to local using a factor of 0.9999. The vertical datum is NAVD88."
When I and another surveying company now occupy some of the original control points using RTN, the horizontal differs by about 138' (vertical is off a few tenths) from those datums.
I don't know how he established his control-paper trail is scarce. We do have a couple of Trimble 4600LS's in the closet. Were they around in '98?
Some other parcels he supplied control for I've checked into under a tenth both vertically and horizontally, but another is 5' off, both H & V. (another may be on NAD27 but that's another story).
Any idea what may have happened here?
International feet vs US Survey Feet?
possible a DA factor. This happens a lot in TN. They come off a monument that the get the coordinates from TDOT and they are Datum adjusted and not true state plane coordinates.
https://www.tn.gov/assets/entities/tdot/attachments/SURVEY_MANUAL.pdf
Since there was definitely a scale factor applied, you need to find out two things: what was the scaling origin point (0,0 or a point on the project?) and was any translation (shift) applied after scaling. These two items are both things that can be figured out with a little bit of intuition and some quick CAD work.
I would guess that if you pick the correct scaling origin point, you'll be able to ignore using a translation.
Almost sounds like the original survey was done in the wrong zone. Maybe he used NY central or Long Island by mistake?
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I vote for autonomous (Trimble "here" position) because this would have been while selective availability was still in effect and could easily account for a discrepancy of this magnitude.
Is there control left? Calibrate to it and check the residuals, rotation and scale and maybe it is good enough. The job is 20 years old sounds like it is a time to sell a redo. Jp
Start simple. Are the coordinates north and east of what you would expect? Probably scaled from 0,0. If his methods were loose he may have also scaled from zero north and the false easting without knowing it.
There are several possibilities, all of which can be checked in a few minutes with a basic calculator.
JerryS, post: 430675, member: 205 wrote: selective availability was still in effect and could easily account for a discrepancy of this magnitude.
How many of the greenhorns remember selective availability or mission planning?
Look for a double transposition in the last three positions, 762 - 627 = 135.
Paul in PA
Gregg Gaffney, post: 430639, member: 1111 wrote: its funny, we typically match others survey coordinates within a tenth or they are way off.
In talking with one of the guys where the info was way off, it turns out that they held scaled info from a quad map and that was fairly common with some guys.
When you really know their info is wrong is when we bring in the Ortho overlay images and they fall where they should with our stuff and the other guys stuff is about a hundred feet away and on the wrong side of the road!
May have the same situation on your job
Ortho photos are an awesome check. I bring them in on almost every job that I do on state plane. It takes 2 minutes and lets you know if something is up.
Multiply the northings and eastings by the scale factor. Do they match the SP coordinates? From my experience, DOT's recommend scaling the SPC's multiplied by the reciprocal of the combined factor with 0,0 as the base to obtain "ground" coordinates. It's an easy reverse to get the SPC when/if needed.
My guess is they used a scaled horizontal point to start from. In my area they are +/- 180m. They were vertical monuments only, which may have been the only direction he cared about. Try jp7191s idea and calibrate.....OR Jerry is right, we are spoiled with automomous positions of 2 or 3 feet lately, and don't think about the old days.
I would guess he scaled his state plane coordinates by 0.9999. Doing that where I am just south of the NY NJ line the horizontal error would be approximately 100'. (The definition for the NY East and the NJ system is the same. it's really one big zone running from the Delaware bay to the Canadian border).
I don't know where you are in the East Zone, some where near Saugerties?
