Module Line Smoothing

The module provides methods for line smoothing including iterative averaging (SIA) and Gaussian filtering.

Iterative averaging (SIA) is described by Mansouryar & Hedayati (2012). A higher smoothing sensitivity results in a stronger smoothing in less iterations and vice versa. The 'improved SIA model' simply applies a preservation factor in the first iteration and then runs the 'basic SIA model' for the following iterations.

Gaussian filtering with shrinkage correction is described by Lowe (1989).

In case the density of line vertices is too high, the 'Line Simplification' tool can be applied first. If the density of line vertices is too low, additional vertices can be inserted by applying the 'Convert Lines to Points' and the 'Convert Points to Line(s)' tools prior to smoothing.

References:
Lowe, D. (1989): Organization of Smooth Image Curves at Multiple Scales. International Journal of Computer Vision, 3: 119-130. (pdf)

Mansouryar, M. & Hedayati, A. (2012): Smoothing Via Iterative Averaging (SIA) - A Basic Technique for Line Smoothing. International Journal of Computer and Electrical Engineering Vol. 4, No. 3: 307-311. (pdf)

Author: V. Wichmann, J. Engels (c) 2014
Menu: Shapes|Lines

Parameters

	Name	Type	Identifier	Description	Constraints
Input	Lines	Shapes (input)	`LINES_IN`	The input line shapefile to smooth.	-
Output	Smoothed Lines	Shapes (output)	`LINES_OUT`	The smoothed output line shapefile.	-
Options	Method	Choice	`METHOD`	Choose the method to apply.	Available Choices: [0] basic SIA model [1] improved SIA model [2] Gaussian Filtering Default: 2
	Sensitivity	Integer	`SENSITIVITY`	Half the size of the moving window [vertex count], controls smoothing sensitivity.	Minimum: 1 Default: 3
	Iterations	Integer	`ITERATIONS`	The number of smoothing iterations [-].	Minimum: 1 Default: 10
	Preservation	Floating point	`PRESERVATION`	The smoothing preservation factor [-].	Minimum: 1.000000 Default: 10.000000
	Sigma	Floating point	`SIGMA`	Standard deviation of the Gaussian filter [-].	Minimum: 0.500000 Default: 2.000000

Command-line

Usage: saga_cmd shapes_lines 7 [-LINES_IN <str>] [-LINES_OUT <str>] [-METHOD <str>] [-SENSITIVITY <num>] [-ITERATIONS <num>] [-PRESERVATION <double>] [-SIGMA <double>]
  -LINES_IN:<str>       	Lines
	Shapes (input)
  -LINES_OUT:<str>      	Smoothed Lines
	Shapes (output)
  -METHOD:<str>         	Method
	Choice
	Available Choices:
	[0] basic SIA model
	[1] improved SIA model
	[2] Gaussian Filtering
	Default: 2
  -SENSITIVITY:<num>    	Sensitivity
	Integer
	Minimum: 1
	Default: 3
  -ITERATIONS:<num>     	Iterations
	Integer
	Minimum: 1
	Default: 10
  -PRESERVATION:<double>	Preservation
	Floating point
	Minimum: 1.000000
	Default: 10.000000
  -SIGMA:<double>       	Sigma
	Floating point
	Minimum: 0.500000
	Default: 2.000000