# Geometry :

Subject: Re: [geometry] fit an ellipse to a polygon
From: Tanaka Simon (tanakas_at_[hidden])
Date: 2013-08-15 11:59:55

On 08/14/2013 05:04 PM, Barend Gehrels wrote:
> Hi Tanaka,
>
> On 14-8-2013 11:55, Tanaka Simon wrote:
>> Hello,
>>
>> I have a model::polygon, and i want to fit an ellipse to it (see link
>> below). do you have suggestions of how to use (built-in)
>> boost::geometry functionality as much as possible?
>>
>> do you have alternative suggestions to characterize the polygon, e.g.
>> to compute the principal axes of the inertia tensor? the solution is
>> allowed to be heuristic.
>
> Interesting problem. You could use distance (point-linestring) to get
> the distance from each point to the ellipse-as-a-linestring. Note that
> if you model the ellipse as a polygon, the distance is zero for all
> points inside, so I would use a linestring here. This ellipse can
> easily be generated from the definition of the ellipse.
>
> To start with you could think of calculating the convex hull of the
> points. That gives a reasonable starting-shape. Its centroid should be
> located in the neighbourhood of the center of the ellipse. And then
> indeed you would need the diameter... You could use the point at the
> furthest location from the ellipse here as a starting point (then you
> also have some idea of the direction of the axis).
>
> Regards, Barend
>
>
>
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simon

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