Unable to project a TIN in ArcMap

Option A

Manually define the projection using the Catalog window in ArcMap:

1. In the Catalog window, navigate to the directory folder where the TIN data is located.
2. Right-click the TIN data, and select Properties.
3. Click the XY Coordinate System tab.
4. Select a coordinate system, and click OK to apply the projection. The TIN data is projected to the respected coordinate system.

Option B

Copy the projection file 'prj.adr' and paste to the original TIN directory:

1. In ArcMap, run the TIN to Raster tool(require 3D Analyst extension).
   a. Navigate to 3D Analyst Tools > Conversion > From TIN > TIN to Raster.
   b. Select a layer by clicking the Input TIN drop-down arrow.
   c. Specify the location of the output raster and save it outside of a geodatabase.
     That is, just save it in a folder with no extension just the raster name, this becomes an Esri grid raster format.
   d. Click Environments to open the Environment Settings dialog box.
   e. Expand the Output Coordinates category and specify the output coordinate system.
   f. Click OK to run the tool. A raster dataset is created.
2. Close ArcMap.
3. Copy and paste the 'prj.adr' file from the raster data folder to the TIN data folder.
   a. Navigate to the location of the raster data in Windows Explorer created in Step 1.
   b. Copy the 'prj.adr' file and paste the file in the location of the original TIN file by overwriting the existing projection file.
4. Re-launch ArcMap and add the TIN data. The coordinate system of the TIN layer is set.

Option C

Note:
This option uses the TIN Node and Create TIN tools, which require a 3D Analyst extension.

1. Run the TIN Node tool to create a feature class from the TIN.
   a. Navigate to 3D Analyst Tools > Conversion > From TIN > TIN Node.
   b. Select a layer as the input by clicking the Input TIN drop-down arrow.
   c. Specify the location of the output feature class.
   d. Click Environments to open the Environment Settings dialog box.
   e. Expand Output Coordinates and specify the output coordinate system.
   f. Click OK, and run the tool. A feature class is created.
2. Run the Project tool to set the projection of the feature class.
3. Run the Create TIN tool to re-create the TIN from the feature class.
     A new TIN with the specified projection is created.