hough ellipse fit inaccurate?

[Kevin Keraudren]

By the way, your ground truth is the values you used when drawing the
ellipse, not the values you detect with a different detection method.

On Thu, Mar 5, 2015 at 10:07 AM, Kevin Keraudren <
kevin.keraudren at googlemail.com> wrote:

> Hi Arno,
> In order to stay on the safe side, why don't you post your actual code,
> with a test case highlighting the error you measure between the true centre
> of the ellipse and the detected one?
> Kind regards,
> Kevin
>
> On Thu, Mar 5, 2015 at 9:53 AM, Arno Dietz <arnodietz86 at googlemail.com>
> wrote:
>
>> Thank you very much Kevin and Johannes.
>>
>> I see the rounding Problem, but it is just for the ellipse drawing. In my
>> actual code I just use the Ellipse center like best [1] and best[2] without
>> rounding. This still produces much more inaccurate ellipse center results
>> than other methods like center of mass for example, althoug
>> <http://www.dict.cc/englisch-deutsch/although.html>h I also use
>> the anti-aliased input image. So is there any possibility to get more
>> accurate results from the hough ellipse fit approach? If not, this is also
>> ok, I just want to be on the safe side that it's not my fault. In that
>> case I will have a look at the suggested approach from Johannes.
>>
>> Am Donnerstag, 5. März 2015 01:21:48 UTC+1 schrieb Kevin Keraudren:
>>>
>>> Hi Arno,
>>>
>>> The first source of inaccuracy comes from your code, you need to round
>>> the values instead of truncating them:
>>>
>>> #yc = int(best[1])
>>>
>>>
>>> #xc = int(best[2])
>>>
>>>
>>> #a = int(best[3])
>>>
>>>
>>> #b = int(best[4])
>>>
>>>
>>>
>>> yc = int(round(best[1]))
>>>
>>> xc = int(round(best[2]))
>>>
>>> a = int(round(best[3]))
>>>
>>> b = int(round(best[4]))
>>>
>>> See resulting image attached.
>>>
>>> Kind regards,
>>>
>>> Kevin
>>>
>>>
>>> A second source of inaccuracy comes from your input ellipse: it is not a
>>> perfect ellipse because you drew it using anti-aliasing.
>>
>>
>>
>> Third, you could fit an ellipse using RANSAC. How does this approach work
>>> for you: http://stackoverflow.com/questions/28281742/fitting-a-
>>> circle-to-a-binary-image/28289147#28289147
>>
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>
>
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