- 19 Replies
- MemberJanuary 31, 2020 at 2:08 am
Not very well stated, but it appears (to me) that they are talking about “NAD83” (realization ???) Universal Transverse Mercator (UTM) Zone 14 Coordinates, SCALED to US Survey Feet.
I see similar “notes” all the time, but don’t really know WHY anybody does that (okay, I have heard a few reasonable explanations, but I am still a little baffled).
The 99th Meridian West is the Central Meridian of Zone 14.
- MemberJanuary 31, 2020 at 2:22 am
I understand that zone 14 is between 96 degrees and 102 degrees west so the central meridian would be 99.
It’s the NAD83 part that baffles me. Are they using NAD 83 lat and long to calculate the UTM coordinates which are metric and then converting those to US Feet?
The one that sent me the note is bidding a construction job but won’t tell me where or what. I’m trying to figure out if they did this intentionally or thats just the way their GIS software is programmed.
- MemberJanuary 31, 2020 at 2:38 am
NAD’83 is the datum. To be a proper UTM statement the epoch should also be included.
The datum is important. NAD’83 elliosoid coordinates based on GRS80 ellipsoid can be hundreds of feet different than NAD’27 datum coordinates based upon Clarke 1866 ellipsoid.
- MemberJanuary 31, 2020 at 3:00 am
We learned about UTM in College in 1978 and I haven’t used it since. From google, it appears UTM came about sometime in the 1940’s. I just couldn’t figure how NAD 83 had anything to do with it. So UTM coordinates vary depending on which version of Latitude and Longitude a person chooses to use. Interesting.
- MemberJanuary 31, 2020 at 3:49 am
I just couldn’t figure how NAD 83 had anything to do with it. So UTM coordinates vary depending on which version of Latitude and Longitude a person chooses to use.
UTM is like SPC or LDP in that all of those are map projections. You have to have an underlying datum to tie down what it is you are projecting.
NAD27, NAD83(xxxx), and the future NAPGD2022 are datums and their realizations that can be expressed in several ways including coordinates on a plane map using one of those projections..
- MemberJanuary 31, 2020 at 4:19 am
I have had to work with this before, and it can lead to a great deal of frustration.
I know of a few Oil and Gas, and Pipeline companies who have all of their field assets located this way.
It is probably prudent to check the conversion from the U.S. Foot coordinate values to metric values to see if they correspond to the same location on the map.
If I remember correctly, it was designed by the military to simplify plotting a course, or trajectory using pythagorean theorem.
The scale factor at the central meridian is 0.9996, and I believe this holds true for most UTM zones.
I remember reading somewhere a long time ago that guaranteed mapping accuracy within the zone was 1:2500, but I cannot find the source of this information, and
I may be remembering this incorrectly.
UTM zones were not truly designed for feet as the measurement units.
In the southern hemisphere, the Equator has a northing value of 10 million meters, and the northing decreases from there as you proceed south.
If you are far enough north in a UTM zone which is using feet for its measurement units, you will see northing coordinates exceed 10 million
unless there is an equation or multiplier used. This can be problematic with certain software packages.
If you are working with the B.L.M. they will require all data provided to them be in NAD83 U.T.M. Meters in the appropriate zone.
I have asked which version or realization of NAD83 was desired (N.S.R.S., 2011 or other) and nobody ever gave me a straight answer.
So I made certain I described what I was providing to avoid a bunch of questions later.
- MemberJanuary 31, 2020 at 5:06 am
I get requests for that sort of thing when working with web developers. They simply say “GPS coordinates” but what they mean is a bit more complex. Typically, they have no idea what they are asking for, what they need, or what I am giving them. But that doesn’t mean they don’t understand the issues, they just speak GIS not surveyor.-All thoughts my own, except my typos and when I am wrong.
- MemberJanuary 31, 2020 at 2:08 pm
I am starting to get it now. I just thought that UTM was tied down long before NAD83 ever came along. So I guess that in 2022, UTM will be moving again, about 2 meters?
UTM would have originally tied to NAD27 in North America and some other datums elsewhere in the world. Back then there were fewer choices of datum.
The military now uses UTM with WGS84(latest flavor), which is a snapshot of IGS at a chosen date. For tactical uses any version of WGS is sufficient.
It is a bit misleading to say UTM will be moving, since saying UTM projection doesn’t specify the datum. But yes, UTM NAPGD2022 will differ from UTM NAD83(2011) by about that much..
- MemberJanuary 31, 2020 at 2:32 pm
UTM was designed for military and large mapping.
Most of my clients that want it are in the oil and gas/pipeline businesses. Of course it’s been around a long time and I only seemed to use it in Montana cause the Lambert projection is very distorted there. I don’t like UTM for boundary or construction, it is Transverse Mercator projections from the equator north and south so imagine how distorted it can become.
However large mappers do like it and use it.
The statement implies that the coordinates are not scaled, that they are based on NAD83 lat, longs for the projections and the zone is given. XY coordinates are a function of geographic coordinates projected to a surface, so it should work fine. The Epoch would be nice to know, but depending on the date of the original data it wasn’t always much of an issue. When NAD83 became available the first Epoch I knew about was 86, it then shifted to 93 which was a large change. Since then there have been many shifts, but early coordinate projects often didn’t identify the Epoch. If it’s expected to show up on site and put the point of a rod with GPS down on a point and have it match this coordinate system, I would expect the surveyor to be disappointed.
Coordinates are usually easy (as long as you don’t expect them to match OPUS/CORS/VRS from the get-go), it’s the elevations that are difficult.
- MemberJanuary 31, 2020 at 4:40 pm
I don??t see an issue
- MemberJanuary 31, 2020 at 6:02 pm
The words “based on” in the description create some doubt. NCDOT uses that term to describe “ground coordinates” derived by some transformation applied to state plane coordinates.
If these are UTM coordinates, then “based on” is meaningless. If they’re UTM coordinates adjusted to fit some concept of “ground”, then there are some issues.
What those words mean is important.
- MemberJanuary 31, 2020 at 6:16 pm
Basis of Bearings and Coordinates shown are Universal Transverse Mercator (UTM), Zone 14, projection referenced to the North American Datum of 1983, 2011 adjustment [NAD83(2011)], expressed in units of US Survey Feet (1 US Survey Foot =1200 meters/3937 feet).
Have at it gang..
- MemberJanuary 31, 2020 at 6:29 pm
and the physical source: description of the published monuments used, or CORS, or PPP.
- MemberJanuary 31, 2020 at 6:41 pm
This note was found on a set of plans. I am not familiar with UTM but this doesn’t even make sense.
For your reference, here is an updated version of Technical Manual 5-241-8 that I used in the US Army as a geodetic surveyor. The answer here is to simply convert the UTM coordinates in NAD83 using GRS80 (in Meters converted from US SVY Feet) to Geographic Coordinates in NAD83 (GRS80). You then convert the Lat/Longs to SPC NAD83 in the area of the project (US SVY FEET). I would base the realization date on the date of the drawing you have, but I would probably assume they are in NAD83 (1986). And I would add that the distortion in UTM far exceeds any you would see in tha SPC system. The only good use to UTM is that it covers large area and you can go from zone to zone easily, but you sacrifice scale distortions.
- MemberJanuary 31, 2020 at 6:49 pm
Sorry, I’m going to be that person.
NAPGD2022 is the geoid model/vertical coordinate reference system. You want NATRF2022.
A projection can affect the offset between the two geodetic datums (that’s badly worded). Between NAD27 and NAD83, you might see 50 meters. Between NAD27 UTM 17N and NAD83 UTM 17N, it’s 110 m north-south and 3-5 m east-west for the location I checked.I’m just one of those evil GIS people. Bwah-hah-hah! Seriously, I do coordinate systems and transformations at Esri.
- MemberFebruary 1, 2020 at 12:24 am
There are some local surveyors that insist upon using UTM because most of their work is inside one zone only and all their work can be on the same system.
- MemberFebruary 4, 2020 at 5:33 am
It’s the projection almost all integrated surveys are expressed in here in Ontario (unless you have an MTO job–they require MTM). NAD83(86) or NAD83:CSRS(whatever epoch–97, 02, or 10) is shooter’s choice.
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