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Target layer: Polyline, Polygon

Description: Drag a selection box. All polylines intersected by the selection box will be smoothed using the parameters assigned. Note that the same functions are available as commands on ET Commands menu and work on the current selection of the target layer.

The smooth  tools are situated by default on the Generalize Densify Smooth Tool Menu. If some of them are used often they can be added to the ET GeoTools toolbar using Tools ==> Customize. 

The parameters for all tools  can be set in the control panel or via a hot key while the tool is activated. In the control panel the user can set whether the parameters dialog to appear for each operation or only when the hot key ("S") is pressed. In the latter case the parameters assigned will be used by the tools until changed.

• Smooth Bezier Tool : Uses Bezier Curve to smooth selected polylines
  • 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
• Smooth B-Spline Tool : Uses B-Spline to smooth selected polylines
  • 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-Spline lie in the convex hull of the original polyline
  • Slower than the Bezier curve, but the results in many cases are much better
• Smooth T-Spline : Uses T-Spline to smooth selected polylines
  • 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

• The "Smoothness" parameter (Used in all smooth tools) 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 polylines.
• 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.

Advantages: 

• Give the user three different method to smooth the geometries
• Available with any type of license (ArcView, ArcEditor & ArcInfo)

Hot Keys: (Pressing these keys when the tool is active will allow changing  the parameters used by the function):

• "S" :
  • Smooth Bezier Tool - sets the Smoothness parameter
  • Smooth B-Spline Tool - sets the Smoothness and Freedom parameters
  • Smooth T-Spline - sets the Smoothness and Tension parameters

Attribute Updates: The attributes of the original polylines are preserved

Notes :

• Since version 9.4 the smooth tools can be used on polygons as well. It is very important to understand that if used on polygons that have neighbors GAPS and/or OVERLAPS might be introduced on the boundaries between the neighboring polygons. Use the smooth tools only on stand-alone polygons!!!!!
• With all methods the Start and End point of the polylines are preserved
• If better approximation is required, the polylines can be densified with the Densify Polylines Tool before smoothing. More vertices will constrain the curves close to the originals
• In some cases Generalize Polylines Tool can be used after smoothing to remove redundant vertices, but preserve the smooth appearance of the polylines

Smooth results: Dashed - Original; Red - Bezier; Green - B-Spline; Blue- T-Spline  (Default parameters)
Bezier
B-Spline Green - Freedom = 3 Blue - Freedom = 5
T-Spline Green - Tension = 30 Blue - Tension = 90

Copyright © Ianko Tchoukanski