Smooth

Smooth Polylines

Running programmatically

Smooth the features of a polyline layer using three different smoothing algorithms

Inputs:

A polyline feature layer
Smooth method
- Bezier curve
  - The curve in general does not pass through any of the control points (vertices of original polyline) except the first and last.
  - The curve is always contained within the convex hull of the control points
  - Approximate the original shape rather freely
  - Fast - good for polylines with many vertices (control points) that will constrain the curve close to the original shape
- B - Spline
  - The curve does not pass through any of the control points (vertices of original polyline) except the first and last
  - Follows better than the Bezier curve the original shape
  - Depending on the "Freedom" parameter the smoothing occurs only in the areas close to a vertex
  - B-Splines lie in the convex hull of the original polyline
  - Slower than the Bezier curve, but the results in many cases are much better
- T - Spline (Tension Spline)
  - The curve passes trough all the vertices of the original polyline
  - The degree of fit can be controlled with the "Tension" parameter
  - Suitable for smoothing curves with comparatively equally spaced vertices
  - Fast with good approximation of the original polyline
Parameters depending on the method
- The "Smoothness" parameter (Used in all methods) defines the number of points in the output curve. The allowed values ( 2 to 20 ) in fact are point multiplier. The number of vertices of the original polyline multiplied by this value will give the number of vertices of the smoothed polyline. The larger the value of the Smoothness parameter, the slower the process will be. In most of the cases a value of 5 (default ) will create smooth and representative polyline
- The "Freedom" parameter (B-Spline only) defines how close to the original polyline the curve will be. The allowed values are from 3 to 10. Smaller values give better approximation. With large values the curve will become very similar to Bezier curve
- The "Tension" parameter (T-Spline only) defines how close to the original polyline the curve will be. Increasing the tension is similar to pulling on the ends of a string constrained to pass through the polyline vertices. allowed values are from 1 to 100.
Optional - Densification tolerance. In some cases the smooth parameters cannot restrict the smoothing enough. The user can restrict the effect of the smoothing by introducing new vertices in the shapes. See Densify function for details
Optional - Generalization tolerance. The smoothing introduces in the shapes many new vertices. The user can decrease the number of vertices by using this option. See Generalize function for details.

Outputs:

New polyline layer
- The output layer will contain all the features of the original data set
- The attributes of the input data set are preserved.

Notes :

With all methods the Start and End point of the polylines are preserved
All the methods implement generic algorithms.
The Generalization and Densification tolerances should be specified in the units of the spatial reference of the input layer

Examples:

Smooth results: Dashed - Original; Red - Bezier; Green - B-Spline; Blue- T-Spline (Default parameters)

smooth1.jpg (23756 bytes)

Bezier

smooth Bezier

B-Spline

Green - Freedom = 3
Blue - Freedom = 5

smooth B-spline

T-Spline

Green - Tension = 30
Blue - Tension = 90

smooth - T-Spline

Running Programmatically

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Parameters

Expression	Explanation
Function Name	SmoothBezier
Function Name	SmoothBSpline
Function Name	SmoothTSpline
<input dataset>	A String representing the input layer. Must be of Polyline type.
<output dataset>	A String - the full name of the output layer.
<Smoothness>	An Integer that defines the number of points in the output curve. The allowed values ( 2 to 20 ) in fact are point multiplier. The number of vertices of the original polyline multiplied by this value will give the number of vertices of the smoothed polyline. The larger the value of the parameter, the slower the process will be.
<Freedom>	Only for B-Spline. An Integer that defines how close to the original polyline the curve will be. The allowed values are from 3 to 10. Smaller values give better approximation. With large values the curve will become very similar to Bezier curve
<Tension>	Only for T-Spline. An Integer that defines how close to the original polyline the curve will be. Increasing the tension is similar to pulling on the ends of a string constrained to pass through the polyline vertices. allowed values are from 1 to 100.
{Densify Before}	A Double representing the Densification tolerance. In some cases the smooth parameters cannot restrict the smoothing enough. The user can restrict the effect of the smoothing by introducing new vertices in the shapes. See Densify function for details
{Generalize After}	A Double representing the Generalization tolerance. The smoothing introduces in the shapes many new vertices. The user can decrease the number of vertices by using this option. See Generalize function for details.

Running the function

ETGWPath used in the table below is the full path to ETGWRun.exe (E.G. "C:\Program Files\ETSpatial Techniques\ETGeo Wizards\ETGWRun.exe")

SmoothBezier

Language	Syntax
Python	subprocess.call([ETGWPath, "SmoothBezier", "input dataset", "output dataset", "Smoothness", "Densify Before", "Generalize After"])
.NET using ETGWRun.exe	StartInfo.FileName = ETGWPath StartInfo.Arguments = "SmoothBezier" "input dataset" "output dataset" "Smoothness" "Densify Before" "Generalize After"
.NET using ETGWOutX.dll	SmoothBezier(input dataset, output dataset, Smoothness, Densify Before, Generalize After)
ArcPy	arcpy.SmoothBezier(input dataset, output dataset, "Smoothness" , "Densify Before", "Generalize After")

SmoothBSpline

Language	Syntax
Python	subprocess.call([ETGWPath, "SmoothBSpline", "input dataset", "output dataset", "Smoothness", "Freedom", "Densify Before", "Generalize After"])
.NET using ETGWRun.exe	StartInfo.FileName = ETGWPath StartInfo.Arguments = "SmoothBSpline" "input dataset" "output dataset" "Smoothness" "Freedom" "Densify Before" "Generalize After"
.NET using ETGWOutX.dll	SmoothBSpline(input dataset, output dataset, Smoothness, Freedom, Densify Before, Generalize After)
ArcPy	arcpy.SmoothBSpline(input dataset, output dataset, "Smoothness" , "Freedom", "Densify Before", "Generalize After")

SmoothTSpline

Language	Syntax
Python	subprocess.call([ETGWPath, "SmoothTSpline", "input dataset", "output dataset", "Smoothness", "Tension", "Densify Before", "Generalize After"])
.NET using ETGWRun.exe	StartInfo.FileName = ETGWPath StartInfo.Arguments = "SmoothTSpline" "input dataset" "output dataset" "Smoothness" "Tension" "Densify Before" "Generalize After"
.NET using ETGWOutX.dll	SmoothTSpline(input dataset, output dataset, Smoothness, Tension, Densify Before, Generalize After)
ArcPy	arcpy.SmoothTSpline(input dataset, output dataset, "Smoothness" , "Tension", "Densify Before", "Generalize After")

Notes:

<> - required parameter
{} - optional parameter
See examples for Python , .NET or ArcPy
The argument separator for StartInfo.Arguments is space. If a string might contain a space, you need to double quote it.

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