Generalise

Applicability:

• Cadcorp SIS Map Modeller
• Cadcorp SIS Map Editor
• Cadcorp SIS ActiveX Modeller

Ribbon Group:

Edit-Clean/Simplify

Conditions for use:

• Item Class: All item classes
• Minimum number selected: 1
• Minimum item status: Editable

Associated commands:

• Clean
• Simplify

Description:

 Generalise generalises geometry using the Douglas-Peucker algorithm (algorithm for reducing the number of points in a curve that is approximated by a series of points).

The Douglas-Peucker algorithm simplifies LineString items while preserving symbols. The algorithm first joins the start and end vertices with a straight LineString item. It then examines the perpendicular distances of the vertices from that LineString item and, based upon a specified threshold, removes vertices within the threshold limit. The simplified LineString items is then redrawn, in a series of successive tests.

Example:

The following example shows three simple cases of LineString item generalisation resulting from different thresholds (distances) being set: the greater the threshold, the greater the simplification of the LineString item (more vertices are removed).

1. To simplify LineString items, select them and select  Generalise.
   
   The Generalise dialog is displayed:

Tolerance

Approximate

Select the Approximate radio button and use the slider to choose an approximate tolerance for the operation.

Exact

Select the Exact radio button and enter an exact tolerance value for the operation.

Click the Apply button to use this exact tolerance value for the operation.

Styles

Before

The first drop-down box selects the pen used to draw the pre-operation item(s).

The first drop-down box selects the brush used to draw the pre-operation item(s).

After

The first drop-down box selects the pen used to draw the post-operation item(s).

The first drop-down box selects the brush used to draw the post-operation item(s).

Preview pane

Shows the pre- and post-operation item(s) overlayed.

Before

Shows the number of vertices and other items for the pre-operation item(s).

    After

Shows the number of vertices and other items for the post-operation item(s).

    Keep original Item(s)

Check the Keep original item tickbox to keep the pre-operation item(s). Uncheck the tickbox if the post-operation item(s) are to replace the original item(s).

2. Enter the required Tolerance and Styles settings.
   
   
3. If you want to keep the original items intact, check the Keep original Item(s) tickbox.
   
   
4. When you are satisfied with the simplification shown in the preview pane, click OK.

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