Raster to TIN

When a raster is converted to a TIN, a certain number of raster mesh points become nodes in the TIN. (A mesh point is a location where four cell corners meet.)

The number of mesh points used to create the TIN is the smallest number that satisfies two conditions. First, the output TIN must cover the entire surface area of the input raster. Second, a user-specified z-tolerance must be met. The z-tolerance is a number that limits z-value differences between the input and output surfaces.

A large z-tolerance allows the TIN surface to conform less closely to the raster. The output TIN has fewer nodes and triangles and the conversion process is faster. A small z-tolerance makes the TIN conform more closely to the raster. The TIN has more nodes and triangles and takes longer to process.

Left: The background raster has been converted to the foreground TIN using a z-tolerance of 50 units. The output TIN has 169 nodes and 269 triangles. (Only nodes and edges are symbolized.) Right: The same raster is converted using a z-tolerance of 25 units. The output TIN has 328 nodes and 563 triangles.

More about z-tolerance

The z-tolerance is the maximum allowed difference between the z-value of an input raster cell and the z-value of the output TIN at the location corresponding to the raster cell center.

To put it another way: suppose you convert a raster to a TIN, then identify a location on the surface to compare the input and output elevation values. If the location you click on corresponds to the center of a raster cell, you can be sure that the elevation difference between the two layers will not be greater than the z-tolerance. If the location you click on does not correspond to a cell center, the elevation difference may or may not be greater than the z-tolerance.

A zoomed-in view of a raster and a converted TIN. The value of the identified raster cell is 2184. The value of the TIN at the location corresponding to the cell center (white dot) is 2159.03. For this location, the difference lies just within the z-tolerance of 25 units.