A surface is described by a set of defining objects: multiple points, edges and/or curves. In this sense they are not "marked" but instead "created" from existing objects.
Note: unlike all other object types surfaces are never displayed in a "marked" form on photographs. They are only visible on the surface table, or if they have sufficient defining objects and are able to calculate their 3D shape, they will be visible in the 3D viewer and projections.
Surfaces are required for texture extraction, orthophoto production, surface drawing and for export to external rendering and animation packages that expect 3D faces, meshes or NURBS surfaces.
Surfaces can be created in eight different ways:
• the path tool
• the triangle tool
• the boundary patch tool
• the loft tool
• the sweep tool
• the revolution tool
• the cone tool
• silhouettes
• the Fit NURBS Surface to Selected Points action
The objects needed to define a surface depend on what type of surface is being created, outlined in the following table:
|
Surface Type |
Minimum objects need to create |
|
Path |
3 points, 1 point and a line or an edge, 2 lines or edges, or 1 curve |
|
Triangle |
3 points or 1 point and a line or an edge |
|
Boundary patch |
2 curves, lines or edges |
|
Loft |
2 objects - curves, lines or edges |
|
Sweep |
2 objects - curves, lines or edges |
|
Revolution |
1 curve, line or edge and 1 line or 1 cylinder |
|
Cone |
1 point and 1 curve (open or closed) |
|
Silhouette |
2 referenced silhouette marks |
|
Fit NURBS Surface |
Minimum of approx. 20 points but depends on the point positions. |