How to Convert a FLO-2D Elevation Grid to a TIN or Raster in ArcGIS 10

For most of you who are already familiar with ArcGIS 10 (and its extensions, 3d Analyst & spatial Analyst), converting between different digital elevation model formats is a no brainer. For example, it would be fairly simple to convert a raster elevation model to a set of mass points, then a TIN, followed by contour lines, and then back to a raster again. This would involve only a series of mouse clicks in the ArcGIS toolbox. But what if someone gave you a FLO-2D elevation grid and you wanted to convert that to another digital elevation model format so that you could use it on another project? First, I would probably ask for a copy of the raw data that was originally used to create the grid, but if it is un-obtainable, then an ArcGIS conversion is your next option.

Before performing a FLO-2D Grid conversion it would be wise to examine it to see if it truly represents the land you are trying to evaluate. In the example that I used to create this guide, the grid was a 50ft x 50ft grid. This would equate to having spot elevations surveyed on the ground at 50ft intervals without consideration for any grade breaks.

To my knowledge there isn’t a ready made tool or downloadable python script available to perform a FLO-2D Grid to TIN or Raster conversion. In the steps that follow, I will explain a simple method that can be used to make this conversion.

Please keep in mind that each time a set of data is converted to another format, some of the accuracy and quality is lost.

Using ArcGIS 10 (ArcEditor license or higher with 3D Analyst Extension) the conversion will take place in the following 3 steps:

1. Calculate the Centroids for the polygonal squares that form the FLO-2D Grid
2. Convert the FLO-2D Grid into a set of points
3. Use 3D analyst to convert the set of points (“mass points”) to a raster, TIN, or contour lines.

If you have an ArcInfo license you may be able to bypass this step by using the “feature to points” option found in the Data Management Toolbox. If you only have an ArcEditor license, then you can create two new fields and use the “Calculate Geometry” tool located within the attribute table. Here is how to do the latter.

1. Open ArcToolbox and Go to Data Management > Fields and double-click the “Add Field” tool.
2. Select the data that you want to add a field to (the FLO-2D Grid) as the input table, the field name should be label as “X” or “Longitude,” and the field type should be “Double.” Click OK.
3. Repeat step 2 but this time the field name should be “Y” or “Latitude.”
4. Once you have finished adding the two new fields, open the attribute table for the FLO-2D grid and right click on the “X” or “Longitude” column and select “Calculate Geometry.”
5. In the Calculate Geometry dialog box, select “X Coordinate of Centroid” from the property drop-down menu. Click OK.
6. Back in the Attribute Table, right click on the Y” or “Latitude” column and select “Calculate Geometry.”
7. In the Calculate Geometry dialog box, select “Y Coordinate of Centroid” from the property drop-down menu. Click OK.

At this point you should have a FLO-2D grid shapefile with X & Y coordinates as well as elevation attributes for each polygon. In the next step I will explain how to convert the grid squares (polygons) into a set of points.

1. Next, in the attribute table, click on the table menu options and select “export.”
2. Specify a new name and location for the table
3. When the export process is complete a message should pop-up asking if you want to add the new table to the current map. Select “Yes.”
4. Next, go to ArcToolbox > Data Management Tools > Layers and Table Views > Make XY Event Layer tool.
5. Add the new table as the XY Table. For the X Field, select the Longitude or “X” field. For the Y Field, select the “Latitude” or “Y” field. Name the new event layer and select the spatial reference or coordinate system. Click OK.

This task is pretty simple and involves only a few short mouse clicks.

1. Right click on the table later and navigate to Data > Export Data
2. Make sure to export all features within the table
3. Specify the output feature class’s name and location. Click OK.
4. When the export process is complete a message should pop-up asking if you want to add the new layer to the current map. Select “Yes.”

At this point you can remove the old table from your layer list and delete it from your computer. You should now have a complete layer of elevation points located at the centroid of each square from the FLO-2D grid.

Your newly created elevation point’s layer can be used as the basis to create any number of alternate digital elevation model formats to fit your needs.

Converting Points to a TIN

1. In ArcToolbox Navigate to 3D Analyst Tools > TIN Management > Create TIN
2. In the first box select the output location of your new TIN
3. In the “Input Feature Class” drop down menu select your points layer
4. Make sure that the height_field is noted correctly with the field that contains the point’s elevation.
5. Click OK.

Converting a TIN to a Raster

1. In ArcToolbox Navigate to 3D Analyst Tools > Conversion > From TIN > TIN to Raster
2. In the “Input TIN” drop down menu select your previously created TIN
3. In the “Output Raster” box select the location and name of your new raster
4. Click OK.

Converting a Raster to Contour Lines

1. In ArcToolbox Navigate to 3D Analyst Tools > Raster Surface > Contour
2. In the “Input Raster” drop down menu select your previously created Raster
3. In the “Output Polyline Features” box select the location and name of your new set of contours
4. Specify a contour interval
5. Click OK.

In addition to the above conversions, there are many other methods available in the ArcToolbox that will allow you to convert between any of the DEM formats.