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About Polys
Each poly has two or more vertices, where each vertex has its own x, y, and z values. A poly is typically horizontal, but it does not have to be. It can be open or closed.
Various basic parameters of a poly are discussed on the page about objects.
A poly has various parameters which can be changed in the Info Panel.
A poly often represents contour lines imported from a DXF file, though you can also draw it from scratch.
Purpose
The purpose of a poly is often to serve as data for a DTM, though a poly can serve other purposes as well.
In the Info Panel, as well as in the dialog box for editing polys, there is a pop-up menu (drop-down list) for setting the purpose. The purpose that you set here only applies if the poly serves as data in a DTM. Typically a poly serves as "Existing data," which means that it would affect the Existing DTM. The other options are various types of modifiers.
A poly can be set to be a modifier of various sorts. This would affect how a Proposed DTM is calculated, if the poly is part of a DTM. If the poly is not a modifier, then it affects how the Existing DTM is calculated; it is used as regular data. If the poly is a modifier, and you are running SimuTerra Pro, then the poly can modify the terrain if a Proposed DTM is calculated.
A modifying poly can influence the Proposed DTM outside of the original triangle (of the Existing DTM) which it falls within. For this to happen, the modifying poly has to be surrounded by a collar. Collars are discussed below. A poly whose purpose is set to road or pad is automatically surrounded by an invisible collar.
A collar indicates the extent to which one or more modifying objects affect the Proposed DTM. This is analogous to a heavy hoop sitting flat on an easily stretchable tablecloth on a table. If you pull up gently from one point within the hoop, the tablecloth within the hoop rises into a cone shape, while there's no effect outside of the hoop.
A poly has to be closed in order to function as a collar, and its purpose has to be set to collar.
Collars which overlap are unionized behind the scenes into one collar.
An open poly can represent a road. The poly serves to represent the centerline of the road; the program automatically calculates the edges of the road, and the daylight line along the length of the road where the proposed terrain meets the existing terrain.
A closed poly can represent a building pad, referred to simply as a pad.
Appearance
You can change the line thickness of the poly, but this will only affect its appearance in the 2D view. Color will affect all views.
You can cause a fence, wall, or pavement to be drawn along a poly in 3D views. You can also have a floor and/or roof drawn in 3D views, creating boxy structures.
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