Command: generalize

Syntax

generalize <num> { ,<elist> ... }

Description

Execute vector generalization on graphic entities (polygons and polylines).

Generalization performs vector smoothing according to a supplied generalization factor (distance). Points which are within distance of each other are removed, and those which are within distance from the centre-line are snapped to form a new center-line.

Parameters

• <num>
  The generalization factor (distance) in modelling units.

• <elist>
  A group/entity list defining which entities are to be generalized. If omitted, the current contents of the these group are generalized.

Switches

• -ar=<nums>
  If this switch is present, it specifies 1 or 2 area thresholds. If any polygon entity has an area less than the first value, then it is removed. If any polygon entity has an area less than the second value (if specified), then it is converted to a simple entity if it is not already, i.e. gstructures or compound children are converted. The removal or conversion is done after the generalization process.

• -com
  If this switch is present, any named entity, gstructure or compound identifiers are compressed as a result of entity removal or conversion. Identifiers with no values (or compounds with no children) are removed. Variable-length identifier arrays with null values are compressed leaving only those elements with non-null values.

• -ef=<filter>
  A filter to be applied to all entities within <elist>, further qualifying which entities are to be generalized. If omitted, the filter current_filter is used.

• -len=<nums>
  If this switch is present, it specifies 1 or 2 length thresholds. If any polyline or vector entity has a length less than the first value, then it is removed. If any such entity has a length less than the second value (if specified), then it is converted to a simple entity if it is not already, i.e. gstructures or compound children are converted. The removal or conversion is done after the generalization process.

Notes

Entities are generalized in place.

Sub-entities of compounds may be generalized in isolation from their parent entities.

The smoothing algorithm used by this command is the Douglas-Peucker Hull algorithm, see:
"D. H. Douglas and T. K. Peucker. Algorithms for the reduction of the number of points required to represent a line or its caricature."
The Canadian Cartographer, 10(2):112--122, 1973.

Examples

Generalize the these group.

generalize 10

Generalize two entities and remove if less than a supplied area.

generalize 10, fred, my_face, -ar=500

See Also