topic MGRS Datum transformation error in Coordinate Reference Systems Questions

MGRS Datum transformation error

DerekFrisby — Mon, 17 Aug 2015 15:11:04 GMT

I am a Marine vet turned academic historian working with MGRS data from the Vietnam War. I have an overlay georeferenced 1:12500 map of Hue, Vietnam (NIMA Reference L909XHUE) with an imagery basemap. When I use ArcMAP MGRS geocoding, my feature points appear significantly off in the newly created feature layer.

When I use this mapplet to geocode, I get a spot on location. The mapplet appears to use the following datum to successfully plot the grid:

Projection: UTM

Datum: Indian 1975, Thailand

Ellipsoid: Everest (India 1830)

Equatorial Radius (m): 6377266.345

Polar Radius (m): 6356075.413

Eccentricity: .081472981

Flattening: 0.003324449

Datum Transformation (local to WGS84): dX (m) 210, dY (m) 814, dZ (m) 289

The mapplet produces the correct point from MGRS translation as follows:

DMS WGS84 LatLong is 16:28:18.87963, 107:35:39.54475

UTM 48Q 777400 1822600

For example, 48Q YD 764266 (Hue, Vietnam) should be at the edge of the Perfume River (known in 1968 as the LCU ramp). However, ArcMAP places it significantly SSE of the location just above a stadium. The incorrect ArcMAP geocoding data transformation (WGS84 or any similar Indian 1975, etc. datum I can find) displays as 48QYD7739522600 MGRS, 107°35'53.094"E 16°28'8.44" or 48Q 777395 1822599 UTM

I have tried without success to find/construct a custom datum in ArcMAP to replicate the above datum. Only mapplet datum plots correctly, but I need to geocode nearly 500 point features.

Any suggestions on how to build a custom datum or is their a native ArcGIS/ArcMAP datum I should use that would be identical?

Suggestions welcome. If you need any more info, please ask.

Re: MGRS Datum transformation error

ChrisDonohue__GISP — Tue, 18 Aug 2015 15:51:48 GMT

Melita Kennedy (ESRI staff) might know the answer to this.

Chris Donohue, GISP

Re: MGRS Datum transformation error

MelitaKennedy — Tue, 18 Aug 2015 18:42:15 GMT

Are you setting a transformation? The equivalent transformation In ArcMap to the one specified in the mapplet is Indian_1975_To_WGS_1984_2. We could also be having an issue between whether the "new" or "old" MGRS style is being used.

Re: MGRS Datum transformation error

DerekFrisby — Wed, 19 Aug 2015 00:59:18 GMT

Melita,

I think you may be on to something. However, as a history professor learning GIS and an ArcMap novice, I could not find WGS_1984_2 or NAD27 datum in the ArcMap program. I am guessing that since there are many WGS_1984 versions that I am missing/overlooking one, and similarly that NAD27 is NAD 1927, but I have no idea which one to use.

I am also guessing a user would use the Projection tool--Convert Coordinate Notation. Then using my csv file, select Indian_1975 for the input coordinate system, but using the WGS_1984_2 as the output file?

would use the Convert Coordinate Notation from Indian_1975 to NAD27, then NAD27 to WGS_1984_2

I know the NAD27 was for the "old" MGRS but I wouldn't know where to begin on translating it to the "new"

Based on the current feature point known correct location and the current projection incorrect location in my arcMap, I am guessing the NAD27 might be a possibility. Any idea on how to, if necessary, adjust for this in the transformation?

PS - Thanks Chris! Melita was an excellent contact.

Re: MGRS Datum transformation error

DerekFrisby — Wed, 19 Aug 2015 02:18:57 GMT

I found this Web Geographic Translator app from the National Geospatial-Intelligence Agency (NGA) that seems to work.

It transforms INH-A1 - Indian, 1975 Thailand (Ellipse: Everest 1830) MGRS data to WGS_84 UTM data with very accurate results.

Is there a INH-A1 datum that ArcMap can utilize to geocode addresses?

Re: MGRS Datum transformation error

DerekFrisby — Wed, 19 Aug 2015 03:00:28 GMT

INH-A1 seems to be the same as Indian 1975 according to another site. apologies. Still confused why geocoding is off the mark. I know I am missing something simple.

Re: MGRS Datum transformation error

MelitaKennedy — Wed, 19 Aug 2015 19:37:58 GMT

More than NAD27 used the 'old' (alternative) MGRS lettering schema. It is ellipsoid-based so Bessel 1841 was one of them, for instance. Although I would expect it to offset even more.

If you try the Convert Coordinate Notation Tool,

Input coordinate system would be GCS_Indian_1975 and output would GCS_WGS_1984.

Input coordinate format would be MGRS and output coordinate format probably DD_2.

Before you open the tool though, right-click ArcToolbox in the ArcToolbox window and open Environments.

Open the Output Coordinates section. In the Geographic Transformations pull-down, select Indian_1975_to_WGS_1984_2 (you can start typing the name and it will scroll the list). OK Environments window, then open the Convert Coord Notation Tool.

Melita

Re: MGRS Datum transformation error

DerekFrisby — Sat, 22 Aug 2015 21:47:31 GMT

I really am perplexed by this. While helpful, I don't think the steps worked, or I performed them incorrectly.

I did notice that the georeferenced map I placed over the basemap has GCS_WGS_1984_Web_Mercator_Auxillary_Sphere

as its spatial reference in layer properties.

Still, 48QYD774226 should come up near feature #101 (LCU Ramp on the Perfume River bank) on the historical map not near the stadium (feature #149)

Here is the map package if you want to see what is what.

Any suggestions?

Hue_City_1968GR.mpk - Google Drive

Re: MGRS Datum transformation error

MelitaKennedy — Tue, 25 Aug 2015 21:48:20 GMT

I think I see. The image is georeferenced to Web Mercator which is based upon a spherical WGS84. You're not going to be able to match the MGRS/UTM values on the map because they're using a different datum.

If I take 48QYD774226, unproject it to Indian 1975 latitude/longitude (16.47033139 107.59849798), transform it with 1304 (16.47191094 107.59431847), then convert it back to MGRS based on WGS84: 48QYD769229

That matches nicely with using the information button in the area of the boat ramp.

I hope this is helpful, and makes sense.

Melita

Re: MGRS Datum transformation error

DerekFrisby — Thu, 27 Aug 2015 00:59:39 GMT

It is very helpful and sounds like the solution. I just wish I knew exactly how to replicate your solution.

I removed the georeferenced map from the table of contents. Then, do I go to the toolbox "Projections and Transformations" to unproject it or do I go to the Data Frame Properties--Coordinate System---Transformations?

I apologize for needing step-by-step instructions.

Re: MGRS Datum transformation error

MelitaKennedy — Thu, 27 Aug 2015 17:42:21 GMT

No problem! Although I'm still trying to figure out what you're doing. Do you want Indian-based MGRS coordinates are features on this map? If so, you could try reprojecting the image (it'll be a copy) from WGS84 to the Indian datum.

Open the Project Raster tool.

Set the output coordinate system to...Indian 1975 UTM zone 48N (WKID 24048).

The tool should want a transformation, use Indian_1975_To_WGS_1984_2.

Melita

Re: MGRS Datum transformation error

DerekFrisby — Fri, 28 Aug 2015 01:01:36 GMT

I am attempting to plot the KIAs from the attribute table. I would like to use the imagery basemap with the historical overlay, but I can live without the historical overlay if it confuses the issue. The project raster tool I think I understand if I wanted to use the overlay.

however, I can't replicate the process you indicated in the Aug. 25 post. No matter what I do I get the same results near the stadium. I guess I am confused by the unproject and convert back procedure.

Do I geocode the addresses first from the table to create a geocoding result layer? Then where do I start to unproject and convert back.

Do I start somewhere else first?

Also, I have to manually tell the transform section to use 1304 and remove the WGS_1984_3 which it seems to want to default to.

Thanks for your patience (again).

Re: MGRS Datum transformation error

MelitaKennedy — Fri, 28 Aug 2015 18:42:46 GMT

If the MGRS data was collected during the Vietnam war, Then it was likely using maps like this one, that were based on Indian 1975. In that case, you'll have to georeference/convert them using an Indian 1975-based map, then convert the results to WGS84. At least, I think! (it's been a long week)

Re: MGRS Datum transformation error

MelitaKennedy — Fri, 28 Aug 2015 18:46:49 GMT

If that's the case, you might look at batch converting using the Convert Coordinate Notation, or NGA's Geotrans software. It will do file-based batch conversions.

Re: MGRS Datum transformation error

DerekFrisby — Mon, 31 Aug 2015 01:18:42 GMT

I think we have lost focus by including the historical overlay.

I am recreating a file without out the overlay to simply try and replicate what you did to get the correct projection. I have found GEOTRANS to be unhelpful.

I am creating a more detailed response and list of my actions for you tomorrow to see where I have gone wrong.

Re: MGRS Datum transformation error

DerekFrisby — Thu, 03 Sep 2015 00:01:46 GMT

Here is what I have done so far and I think we are real close. Please see what you can do to zero us in on this issue.

Choose World Imagery as Basemap

Add “SAMP_YD_CAS.csv” to ToC (This results in the creation of columns “MGRS_UTM_X” and “MGRS_UTM_Y” coordinates in the attribute table and lists for HOOVER (48QYD774266): 107.598124 16.469013 [slightly different from 107.59849798 16.47033139 that you had referenced on Aug. 26 reply. What did I do differently?.]

Select “SAMP_YD_CAS.csv” and select View—Data Frame Properties—Set Coordinate System to “Indian_1975” and the Transformation from “WGS_1984” to “Indian_1975” using 1304 transformation (Indian_1975_to_WGS_1984_2)

Open ArcToolbox---Convert Coordinate Notation---Select “SAMP_YD_CAS.csv”---Input “Indian_1975” to Output “WGS_1984”---Creates a “ConvertCoordinat” layer in ToC

Open ArcToolbox---Define Projection--- Select “ConvertCoordinat” layer---Select Coordinate System “Indian_1975”

This yields a feature for example for HOOVER (YD774226 at “107.598115 16.469033” – Close but still about 135m SSW of where I want it (or think it should be)

Suggestions?

Re: MGRS Datum transformation error

MelitaKennedy — Thu, 03 Sep 2015 15:32:45 GMT

Before you project the layer, try setting the same transformation in the ArcToolbox properties:

Right-click ArcToolbox in the ArcToolbox window and select Environments

Open Output Coordinates

Under Geographic Transformations, click the pull-down and select Indian_1975_to_WGS_1984_2.

Then try running Convert Coordinate Notation.

Melita

Re: MGRS Datum transformation error

DerekFrisby — Mon, 07 Sep 2015 20:40:53 GMT

I can't make this work. The most frustrating thing is that on the map YD774226 shows exactly where it needs to me when adding XY data individually, but when I input the table and try to place the coordinates on the map, it still shows up SSW of that point. AGH! This is my email. Derek.Frisby@mtsu.edu Can someone please email me so we can set up a phone call?