How to Convert ESRI TIN to Elevation Raster?

This article and video demonstrates how to convert an ESRI TIN file to an elevation raster using ArcGIS and the 3D Analyst extension.

TIN versus Elevation Raster

A Triangulated Irregular Network (TIN) is a vector representation of a ground surface. An elevation raster (grid) dataset represents the height of the ground using pixel values.

While both formats store elevation data, TINs are less widely supported in GIS and CAD packages. They are also more computationally intensive to render, and large datasets can take a long time to draw on screen. In addition, ESRI TIN and Terrain Datasets are in proprietary format and are only supported by ESRI software products making it very difficult to share with other software applications.

Elevation rasters on the other hand are faster to render, and are supported by a wider variety of software applications.

Prepare ArcGIS for Geoprocessing

To manipulate TIN elevation data, the 3D Analyst extension must be enabled.

To enable the 3D Analyst extension, follow these steps:

1. Open ArcCatalog.
2. From the ArcCatalog main menu, select Customize | Extensions to display the Extensions dialog box.
   
3. From the displayed dialog box, check the 3D Analyst option to enable the extension. Then, click the [Close] button.
   

ArcGIS has two available modes for processing data:

• Background Geoprocessing
• Foreground Geoprocessing

Both modes will work for this tutorial; however they will affect what you see on screen. This tutorial will use foreground geoprocessing as it provides more diagnostic information in case of errors.

To enable foreground geoprocessing, follow these steps:

1. From the main menu, select Geoprocessing | Geoprocessing Options to display the Geoprocessing Options dialog box.
   
2. From the displayed dialog box, uncheck the Enable Background Geoprocessing option. Then click the [OK] button.
   

Validate TIN Data

Before converting the TIN to an elevation raster, it is important to check the integrity of the TIN data to determine if any modifications need to be made.

To validate the TIN data, follow these steps:

1. Create a working directory, and copy the TIN file to this directory.
2. In ArcCatalog, right click on the TIN file entry and select Properties from the displayed context menu. This will display the TIN Dataset Properties dialog box.
   
3. From the displayed dialog box, select the XY Coordinate System tab and note down the referenced coordinate system. Do the same for the Z Coordinate System tab.
   
   In this example, the XY coordinate system is NAD1983 Arizona State Plane Central FIPS 0202 International Feet. The Z (height or elevation) coordinate system is undefined. However, by comparing the TIN height against other elevation data in the area it is possible to determine the TIN elevation units. In this example the project is near Tucson, AZ and we were able to determine that the TIN elevation units are in feet.
4. Open ArcMap. Click the Add Data button, and open the TIN file.
   
5. Wait for the TIN to draw. This may take some time. When the TIN has finished drawing, you should see lines and shaded areas.
   

In the above illustration the red and blue lines actually represent two different elevation point data sets that were used to construct the TIN. This elevation point data are used as the vertices of the TIN triangles. In the above illustration the TIN triangle edges are not visible. However, the triangle edges represent interpolated elevations and the shaded areas between the the triangle edges represent linear elevation (flat planar) surfaces. ArcGIS uses the linear elevation surfaces to compute elevations for locations within the areas between the triangle edges.

Delineate TIN Elevation Data Area

In this example the shaded areas extend beyond the extents of the elevation point data (i.e., TIN vertices). By default, ArcGIS constructs a convex hull boundary of the elevation data and constructs a TIN within it. However, as can be seen below, the TIN triangles (shaded areas) extend beyond the elevation point data. This will be corrected by delineating the TIN elevation data area.

To stop ArcGIS constructing TIN triangles beyond the extents of the elevation point data, we will define elevation area limits where there is valid elevation data. It is important to perform this step before converting the TIN to an elevation raster or otherwise the elevation raster will contain the same invalid elevation areas as the TIN.

To delineate the TIN elevation data area, follow these steps:

1. In ArcCatalog, click the Search button. This will open the Search panel.
   
2. In the displayed Search panel, select Tools, type Delineate TIN data area in the search field, and then press Enter. The software will list the Delineate TIN Data Area tool in the search results.
   
3. Click on the blue tool name to display the Delineate TIN Data Area dialog box.
4. In the Delineate TIN Data Area dialog box shown below, select the TIN file for the Input TIN field by clicking the browse button.
5. In the Maximum Edge Length field, enter an edge length of 1000.
6. In the Method dropdown combox box, select the PERIMETER_ONLY option.
7. Click the [OK] button to run the Delineate TIN Data Area tool on the selected TIN.
   

The Delineate TIN Data Area tool works by removing TIN triangles that have a triangle edge longer than the specified maximum edge length. The concept is that most valid elevation areas are made up of TIN triangles with short edge lengths, and invalid elevation areas have TIN triangles with longer edge lengths. Generally, invalid elevation areas occur on the perimeter of the TIN dataset due to the creation of the convex hull area. However, if there are large areas inside the TIN that do not contain elevation data (e.g., lakes and rivers), change the Method to All.

There is no rule on what value to enter for the Maximum Edge Length field. Smaller values will remove more triangles, but can also remove valid elevation areas from the TIN dataset. Larger values eliminate fewer triangles, but can leave invalid elevation areas in the TIN dataset. Trial and error is used to determine an appropriate value to use. The Delineate TIN Data Area tool can be run multiple times on the same dataset; each iteration overwrites the previous results. It is not necessary to run the Delineate TIN Data Area tool on a fresh copy of the TIN each time.

The TIN’s XY coordinate system determines the unit of measurement for the Maximum Edge Length field. For example, if the TIN is in NAD83 State Plane coordinates, the units will be in feet. If the TIN is in WGS84 UTM coordinates, the units will be in meters.

TIN elevation data set after running Delineate TIN Data Area tool with different Maximum Edge Length values. From top to bottom, 100 ft, 1000 ft, and 5000 ft.

Convert TIN to Elevation Raster

Once you are satisfied with the delineated TIN elevation data area, it is ready to be converted to an elevation raster.

To convert the TIN to an elevation raster, follow these steps:

1. In ArcCatalog, click the Search button. This will open the Search panel.
2. In the displayed Search panel, select Tools, type TIN to Raster in the search field, and then press Enter. The software will list the TIN to Raster tool in the search results.
   
3. Click on the blue tool name to display the TIN to Raster dialog box.
4. In the TIN to Raster dialog box shown below, select the TIN file for the Input TIN field by clicking the browse button.
5. In the Output Raster field, select a destination folder and file name using the browse button.
6. In the Output Data Type dropdown combo box, select the FLOAT option.
7. In the Method dropdown combo box, select the LINEAR option.
8. In the Sampling Distance dropdown combo box, select the CELLSIZE option and enter the size that each raster pixel should represent (e.g., enter CELLSIZE 10 for 10×10 ft pixels).
9. In the Z Factor field, use the default value of 1.
10. Click the [OK] button to run the TIN to Raster tool.
    

When entering a file name for the output raster, the file extension determines what format the raster will be saved as. For example, entering “elevation.img” will save the elevation raster as an ERDAS Imagine elevation file. Leaving the extension blank will save the elevation raster as an ESRI binary grid elevation raster. In the above dialog box, the raster is saved as an .img file as ERDAS Imagine elevation raster files do not have file name or size limitations as do ESRI elevation grid files and GeoTIFF files.

Floating point (float) elevation rasters are the default raster type. Float elevation raster files store elevation information with a higher precision than integer elevation rasters as they store the elevation data with decimal information (e.g., 10.35 feet versus 10 feet). The downside of float elevation raster files is the extra precision makes the files larger than integer elevation raster files.

The Z Factor field is used to convert between different elevation units. For example, if the TIN’s elevation units are in meters and you need the elevation raster units in feet, you would enter a Z Factor of 3.28084 (i.e., 3.28084 feet = 1 meter). Conversely, if the TIN elevation units are in meters and you need the elevation raster units in meters, you would enter a Z Factor of 0.3048 (i.e., 0.3048 meter = 1 foot).

Check the Converted Raster Results

Once the TIN to Raster tool has completed, open the output raster in ArcMap to check for any errors. The below image shows the computed raster elevation results.

If you want to view a colorized version of the image, right click in the Table Of Contents on the image entry and select Properties from the displayed context menu. The Layer Properties dialog box will be displayed.

In the displayed dialog box, select the Symbology tab. Then, from the Color Ramp dropdown combo box, select an appropriate color ramp. To add a 3D effect to the displayed elevation raster, check the Use hillshade effect option. These settings do not alter the raster elevation data, only how it is displayed in ArcMap.