------------------------------------------------------------------------- This list (NEARC-L) is an unmoderated discussion list for all NEARC Users.I asked one of our projection experts, Melita Kennedy, to clarify:
If they’re in ArcMap, you have to set the transformations. I can’t tell if that was done or not. You should install the ArcGIS Coordinate Systems Data setup if you’re using a recent release.
ArcMap (and ArcGIS Pro) will transform as well as project data but you usually have to tell the software which transformation to use—
ArcMap
1. Open data frame properties
2. Select the Coordinate System tab
3. Click the Transformations button
4. Top box lists all unique geographic coordinate systems (datums). Pull-down is the map’s current geographic coordinate system. Bottom pull-down will display available transformations. Change the selected GCS in the top box, the bottom pull-down’s list will change. List is sorted by extent. If there are two transformations with the same extent overlap (versus data and map), we sort by accuracy.
Because the points overlaid in the second scenario, that sounds to me as if transformations were set. I wouldn’t expect them to exactly overlay though because the transformations are best-fit and won’t match coordinates of resurveyed control points.
Regards,
Melita
She also said you can reach out to her directly with any questions, her email address is mkennedy at esri.com.
Cheers,
Shaun
From: Northeast Arc Users Group <[log in to unmask]> on behalf of Dan Martin - NOAA Federal <[log in to unmask]>
Reply-To: Dan Martin - NOAA Federal <[log in to unmask]>
Date: Wednesday, October 10, 2018 at 12:01 PM
To: "[log in to unmask]" <[log in to unmask]>
Subject: Re: Transforming xy data
Kieth,
You are correct in your analysis, but that is not the situation. The five individual points plotted in the same corresponding locations as their counterpart from the combined file, not on top of each other. Paul Rooney sent me a link which probably explains the problem/misunderstanding. ArcMap PROJECTS on the fly, it does not TRANSFORM o the fly. Will have to perform an individual transformation on each file. Here is the link Paul provided......Thanks Paul!!! https://support.esri.com/en/technical-article/000002828
Daniel J. Martin
Northeast Regional Geodetic Advisor(ME, NH, VT, MA, CT, RI, NY, NJ)
NOAA/NOS/National Geodetic Survey
Email: [log in to unmask]Cell: 240-676-4762
On Wed, Oct 10, 2018 at 11:46 AM Miller, Keith <[log in to unmask]> wrote:
I may be showing my ignorance here, but I would think that the fact that the five different lat longs all plotting at the same point showed that there WERE transformations taking place. If the “points” were supposed to represent the same physical location on the earth, then they SHOULD all overlap, as long as you tell ArcGIS the proper coordinate system used, which is what it sounds like you did in the second step. The first step showed the problem with not having proper documentation, in that the same “point” showed up in five different places on the map. What am I missing?
Sincerely,
Keith Miller
From: Northeast Arc Users Group [mailto:[log in to unmask]] On Behalf Of Christina Herrick
Sent: Wednesday, October 10, 2018 10:49 AM
To: [log in to unmask]
Subject: Re: Transforming xy data
I'd be curious to know if anyone figures this out. I gave it a try and I'm also having the same issues.
Christina HerrickResearch Scientist
V: 603.862.2639 | F: 603.862.0188
University of New Hampshire
Institute for the Study of Earth, Oceans, and Space
Earth Systems Research Center
Morse Hall, 8 College Road
Durham, NH 03824
ResearcherID: O-3375-2017
ORCID ID: 0000-0002-8384-9450
On Wed, Oct 10, 2018 at 10:19 AM Dan Martin - NOAA Federal <[log in to unmask]> wrote:
Good morning,
I will try to make this as understandable as possible:
Objective: To show why proper metadata (datum/realization wise) is important.
I got the datasheet for a geodetic control point in NJ. It has a current NAD 83(2011) lat/lon. It also has many superseded coordinates (Lat/Lon) going all the way back to NAD 83(1986).
I created a map in ArcMap, and established the data frame coordinate reference to be NAD 83(2011)
I then created a .txt file of the various NAD 83 positions that reflected the various realizations 2011, 2007, 1996, 1992, 1986.
I added the xy data to the map and told ArcMap that they were Geographic NAD 83 (2011) (which of course they were not). As one would expect, I got 5 dots on the map with a spatial separation that reflected the differences between the 5 realizations.
Next I created one file for each coordinate, and added each file one at a time. This time, I told ArcMap that the coordinate system for each file was actual realization of the position, i.e., when adding the NAD 83(2007) lat and lon, I told ArcMap that the coordinate system of the position was in fact NAD 83(2007). The result was 5 dots that plotted exactly on top of the other 5 dots, i.e., no transformation took place?
Am I doing something wrong?
Thanks for any input. I have attached the files if anyone wants to test this them selves. I have provided the files to some of my counterparts and they experienced the same.
Dan
Daniel J. Martin
Northeast Regional Geodetic Advisor(ME, NH, VT, MA, CT, RI, NY, NJ)
NOAA/NOS/National Geodetic Survey
Email: [log in to unmask]Cell: 240-676-4762
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