Simplify sketch paths using Douglas-Peuker algorithm

[danielworkman]

• Added an implementation of the Douglas-Peuker algorithm for simplifying polylines/paths
• This gets run on a sketch path a) each time a user lifts their finger after making a new sketch and b) when loading a saved survey. This means that older surveys saved before the addition of this enhancement can get the same performance gains.
• The calculated epsilon value is quite crude but can be improved after additional testing if necessary
• Added a "debug mode" option to the "Dev" menu to toggle the drawing of path points which is handy when analysing epsilon values
• Using the current epsilon calculation there was a reduction of 54% of the total sketch coordinates after loading a large test project

[danielworkman]

If you look at the implementation of the algorithm you can see that that will not be the case. You could run the algo 1000 times on a geometry simplified just once and nothing would happen

On Thu, 10 Jun 2021 at 08:36, Rich Smith @.***> wrote:

@.**** commented on this pull request.

In app/src/main/java/org/hwyl/sexytopo/control/io/basic/SketchJsonTranslater.java https://github.com/richsmith/sexytopo/pull/150#discussion_r648927227:

@@ -161,6 +160,11 @@ public static PathDetail toPathDetail(JSONObject json) throws JSONException { }

     PathDetail pathDetail = new PathDetail(path, colour);

+

• double epsilon = Space2DUtils.SketchEpsilon(pathDetail);
• List simplifiedPath = Space2DUtils.Simplify(path, epsilon);
• pathDetail.setPath(simplifiedPath);

You probably understood what I meant, but just checking: we don't just need the result to be the same for the same input, but we also need the result to be the same for feeding the output of the first pass back into the algorithm. That is, we don't want the paths to get progressively simpler every time the file gets loaded.

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[richsmith]

If you look at the implementation of the algorithm you can see that that will not be the case. You could run the algo 1000 times on a geometry simplified just once and nothing would happen

I guess I should stop being lazy and understand what the algo does!

[...]

OK, think I understand it now. Quite elegant. Yep, should be fine.