[GIS] How to reproduce Smoothing from Generalizer Plugin in v.generalizer in Processing Toolbar using QGIS

generalizationgrassqgisqgis-2.4smoothing

I´d like to reproduce the smoothing operations done with the Generalizer Plugin inside the v.generalizer Toolbox so I can use them on a polygon layer instead of only on a line layer.

I tried different values for different settings but I just don´t see how to get the same results using the v.generalizer algorithm in the Processing toolbar.

Simply said: To which values in the v.generalizer algorithm window do the settings I see in the generalizer plugin correspond to?

Here are the settings I´d like to use and the results I get:

1) Hermite

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2) Chaiken

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Now in the v.generalize windows there are so many options and values but nothing there is named the same as the ones in the generalizer plugin…

I hope you can help me, I´m also grateful for hints to other ways to smoothen my polygons in a way that produces results similar to those in the pictures above.

I tried using the v.generalizer toolbox after reading these two question:

Is there a QGIS bezier curve tool?

Is there a way to render lines with a smooth (bezier) curves in QGIS?

I'm using QGIS 2.4.

Best Answer

There is a difference in wording but I think the options from the Generalizer plugin exists in the v.generalizer interface. Using Google Translate (yes, not the best thing to use) for the Generalizer Homepage, we can find a description on each algorithms used and their corresponding parameters.

In terms of Hermite Spline Interpolation, the homepage tells us:

Threshold - Determines the distance between the created points.

Thightness - Factor determining the degree of bending of the resulting line.

Now looking at the Help section in v.generalizer, we can try and find those parameters mentioned above. For Threshold:

threshold=float
Maximal tolerance value <------ This is in the options.
Options: 0-1000000000

For Thightness:

Minimum angle between two consecutive segments in Hermite method <--- This is in the options.

Hermite

In terms of Chaiken's Algorithm, the homepage tells us:

Level - Determines the number of iterations of the algorithm.

Weight - Determines the shear rate, the bigger the fillets are closer to the line of nodes.

Now we look at the Help section in v.generalizer again. For Level:

Number of iterations <----- This is in the options.

For Weight:

betweeness_thresh - It denotes to what extent a line is in between the other lines in the network (unsure if this is the correct parameter!)

Chaiken

I could be wrong with this, in which case hopefully others can advise and/or re-edit this post.

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