Clean/Simplify (Process operations)

Generalises geometry using a variation of the Douglas-Peucker algorithm that is limited by the number of output points.

Number of points*: The number of output points, as a simple value, or as an expression, eg '10' or 'Int(_np&/10)'.

The following examples show the effect of increasing the Number of points value.

Initial Polygon Item:

Number of points = 50:

Number of points = 100:

Number of points = 500:

Generalises geometry using the Douglas-Peucker algorithm.

Tolerance*: The Douglas-Peuker algorithm tolerance, as a simple vale, or as an expression, eg '12.34' or '0.1234*_length#'

All vertices in the simplified geometry will be within this distance of the original geometry.

The following examples show the effect of increasing the Tolerance value.

Initial Polygon Item:

Tolerance = 50:

Tolerance = 100:

Tolerance = 300:

Generalises geometry using the Perpendicular Distance algorithm.

Properties

Repeat*

The number of times to repeat the algorithm, as a simple value, or as an expression, eg '4' or 'Int(_np&/50)'

Tolerance*

The Perpendicular Distance algorithm tolerance, as a simple value, or as an expression eg '12.34' or '0.1234*_length#'

The following examples show the effect of increasing the Tolerance value.

The original map:

Tolerance = 50:

Tolerance = 500:

Tolerance = 1000:

Generalises geometry using the Radial Distance algorithm.

Tolerance*

The Radial Distance algorithm tolerance, as a simple value, or as an expression eg '12.34' or '0.1234*_length#'

The following examples show the effect of increasing the Tolerance value.

The original map:

Tolerance = 50:

Tolerance = 500:

Tolerance = 1000:

Generalises geometry using the Reumann-Witkam algorithm.

Tolerance*: The Reumann-Witkam algorithm tolerance as a simple value or as an expression eg '12.34' or '0.1234*_length#'

The following examples show the effect of increasing the Tolerance value.

The original map:

Tolerance = 50:

Tolerance = 500:

Tolerance = 1000:

Removes duplicate items based on an expression.

Expression*

The test expression, eg 'FC&' or 'building_type$="industrial"'

In this example, the overlay Units contains Industrial and Office buildings:

Select the Units overlay:

Click Next.

The Processing Operations dialog will be displayed.

Select General > Filter in the left-hand pane and click the right arrow button to add Filter to the right-hand pane.

Click the ... button to open the Expression Builder window.

Set the Process command General > Filter to show only the Industrial buildings and click OK.

This will be building_type$="Industrial"

Click OK.

The Filter now appears in the Processing Operations window:

Click Next to open the Processing Output dialog. Select the required output and click Finish.

This opens the Processing Input window again:

Check the Units overlay is still selected and click Next.

The process will run and the final display will be shown:

The new overlay will be displayed with all duplicates removed.

Note: The item remaining will be the last item drawn or edited.

Removes duplicate items based on their geometry.

Removes self-intersections, eg a bow-tie.

Removes segments shorter than a tolerance.

Tolerance*: The tolerance as a simple value or as an expression eg '0.1234' or '0.001234*_length#'

Removes vertices that cause a spike.

Tolerance*: The tolerance in degrees, as a simple value or as an expression, eg '0.1' or 'Acos(0.999998)*180/3.14'

Removes vertices between straight, or near straight segments.

Tolerance*: The tolerance in degrees as a simple value or as an expression eg '0.1' or 'Acos(0.999998)*180/3.14'.

Simplifies the geometry of an item so that it matches the OGC 'simple' form (eg by removing all self-intersections).