How Interpolate Polygon to Multipatch (3D Analyst) works

The Interpolate Polygon To Multipatch tool produces a multipatch feature class using a triangulated irregular network (TIN) or terrain dataset and a polygon feature class as input. The portion of the surface within each polygon is extracted as a multipatch-based feature. Multipatches capture the 3D representation of the TIN or terrain dataset surface in their geometry, including interior areas as well as perimeters. Attributes from the input records are carried over to the output.

Each input polygon has its boundary profiled on the TIN or terrain dataset surface. Heights are obtained using linear interpolation. Sampling occurs at each input vertex and wherever the boundary line intersects surface triangle edges and nodes. This natural densification captures the full definition of the linear surface using a minimal number of samples. Then, all nodes that fall within the polygon are extracted. The nodes are retriangulated in a new memory-based TIN, and the 3D polygon boundary is enforced as a clip polygon. The triangles of this new TIN are then extracted in a series of strips that are used to define a multipatch-based feature.

The {max_strip_size} parameter specifies the maximum number of vertices allowed in any triangle strip used in multipatch construction. While ArcGIS doesn't have any particular size limit or preference, some 3D graphic cards might. Triangle strips are input directly to the 3D graphics application program interface (API) for rendering. The default {max_strip_size} value is 1024.

The {z_factor} is used to convert z-values from one unit of measure to another (for example, feet to meters). Heights derived from the input TIN or terrain are multiplied by this factor during multipatch construction.

The Interpolate Polygon To Multipatch tool is useful when the 3D surface within a polygonal area needs to be treated as a feature. One example of its use is as a refinement of polygon draping within ArcScene. Users want the polygons to follow the surface, both around their perimeter and the their interior areas. The problem is that polygons are only defined by their boundary lines. Their interiorsare undefined in 3D space. So polygons don't render as people would expect. One solution is to rasterize the polygons and drape the rasters, as is done onthefly in ArcGlobe. Another approach is to use this tool to convert the polygons to multipatches, a geometry whose internal area is defined in 3D space, and render the multipatches.

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