MGRS Datum transformation error

[DerekFrisby]

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.

[MelitaKennedy]

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

[DerekFrisby]

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).

[MelitaKennedy]

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)

[MelitaKennedy]

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.

[DerekFrisby]

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.

[DerekFrisby]

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?

[MelitaKennedy]

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

[DerekFrisby]

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?