Creating 3D features

3D features differ from 2D features in that they store a z-value as part of their spatial definition. 3D features can be created from scratch (you define a new feature class to be 3D when you create it), or they can be converted from existing 2D features.

Since 2D features can already be displayed in 3D, the main advantage of 3D features is one of convenience. If you frequently add the same 2D layer to ArcScene, you may get tired of setting its base heights every time. By converting it to 3D, you no longer have to do this.

To convert a 2D layer to 3D, you need the missing ingredient: z-values. There are three ways to get z-values:

· From a raster or TIN layer that shares a common spatial extent with the 2D features

· From an attribute in the 2D layer attribute table

· By typing a value (which is then applied to all features in the 2D layer)

If the 2D layer is a point layer, each feature gets a z-value. If it is a line or polygon layer, each feature vertex gets a z-value.

More about getting z-values from rasters and TINs

When the source of z-values is a raster, the z-value assigned to each point feature depends on the point’s location within a cell and the values of nearby cells.

A point layer, symbolized in light blue, has been converted to 3D using the raster as the source of z-values. The raster cell values are shown in white circles. The interpolated z-values of the points are labeled in dark blue.

For line and polygon layers, a z-value is interpolated for every feature vertex. Additional vertices are created at intervals equal to the grid cell size.

A line feature, symbolized in purple, is converted to 3D. Z-values are interpolated for the original 2D line vertices (shown in red) as well as for a new vertex (blue).

When the source of z-values is a TIN, the z-value assigned to each point is identical to the TIN elevation at the point’s location. For line and polygon layers, a z-value is interpolated for every feature vertex. Additional vertices are created wherever a feature crosses a triangle edge.

A line feature, symbolized in red, is converted to 3D. Z-values are interpolated for the original 2D line vertices (red) and for three new vertices (blue).

Digitizing 3D features

You can digitize 3D features in an ArcMap™ edit session if your map document contains a raster or TIN layer and a feature layer that stores z-values. You can specify that a feature layer store z-values when you create it in ArcCatalog.

The 3D digitizing tools (one for points, one for lines, and one for polygons) are located on the ArcMap 3D Analyst toolbar.

Digitized 3D features have a z-value for every vertex you digitize. Just like features that are converted from 2D to 3D, they also have vertices at cell-size intervals (if you are digitizing on a raster) or where features cross triangle edges (if you are digitizing on a TIN).

A 3D polygon digitized on a TIN layer in ArcMap.