Points, Features, Attributes and Feature Properties
Updated October 17, 2017
This article applies to:
- Terrain 3D
- Terrain Forestry
- RoadEng Civil
- RoadEng Forestry
A feature is a collection of points such as a contour line, a lake boundary or a spot elevation point. Bitmap images are also considered to be features (in this case the corners are the points). Many operations in Terrain apply to features or groups of features such as formatting, moving, deleting etc. Feature attributes can be assigned to the features.
Features consist of 1 or more xyz coordinate points. Point attributes can be assigned to individual points.
Figure 1: Figure 1: Single and multiple point features
Attributes are the properties of a particular object. They can be things like line type and color, which are editable feature attributes, or things like the number of features in a file which is a read-only attribute.
Attributes can be viewed through the Status Window, the Features Window or the Points Window. There are three broad classifications of attributes and they are as follows:
- Point Attributes - properties of a point on a feature.
- Feature Attributes - properties of a feature.
- File Attributes - properties of all the features and the file as a whole.
Attributes are grouped together in categories. Many categories are pre-defined, but you can create your own attribute definitions by adding a new category using the Attributes Setup Dialogue. An example of a pre-defined category is Format. The Format category contains feature attributes such as line type, color, and hatch. These attributes are not read-only, so you can modify them in the Features Window.
Fixed Feature Attributes (Feature Properties)
Every feature has a set of fixed attributes (additional attributes are optional). These attributes are saved in a feature header.
The following properties are saved with every feature:
Each feature has a unique name consisting of a 50 character Alphanumeric Id portion and a Numeric Id. It is possible to have more than 1 feature with the same Alphanumeric ID e.g. STREAM-1, STREAM-2 etc. The feature name is not case sensitive i.e. " RightOfWay11" = " RIGHTOFWAY11".
Line-type, Color, Symbol & Hatchtype
Visibility e.g. displayed or hidden
Feature points are connected by lines or isolated (refer to Figure 2-4)
Feature points have elevations
Feature points will be included in the TIN model
Feature is a breakline (TIN modeling)
Feature represents a hole with negative area. This option can be used with TIN Boundary below.
Feature is a TIN boundary
Surface Volume Boundary
Feature is used as a polygon to accumulate volumes in the volume calculations.
Note: When working with very large data sets it is not a good idea to use single point features because the memory overhead for the feature header can be significant. If possible, make sure that data are grouped into features containing a number of points (1000+).
Figure 2: Connected and unconnected feature property