Posted by
Rasband, Wayne (NIH/NIMH) [E] on
URL: http://imagej.273.s1.nabble.com/Feret-measurements-tp5000233p5000235.html
On Sep 27, 2012, at 3:59 PM, Rodrigo Gonçalves wrote:
> Hi guys,
>
> I found that the definition of the Feret's measurements might change for different software/webpages.
>
> To test how ImageJ goes with this, I opened a new image in Fiji under Windows, created a 'perfect' circle pressing CTRL to keep the ratio aspect, and then filled it and measured it.
>
> The max and min Feret's look ok, but then I have FeretX and FeretY which I don't fully understand.
>
> From the ImageJ user guide (
http://rsbweb.nih.gov/ij/docs/user-guide.pdf and
http://rsbweb.nih.gov/ij/docs/guide/146-30.html) I would expect to obtain the length of the object’s projection in the X (FeretX) and Y (FeretY) direction. If this is correct, then in a perfect circle MaxFeret, MinFeret, FeretX, FeretY should all have the same value, right? Because I expect the projection of a circle on the X axis will equal de circle's diameter, is that so?
>
> But I get a Feret's diameter = 288 while FeretX and FeretY are 78 and 73, respectively.
>
> What am I missing here?
FeretX and FeretY are the starting coordinates of the Feret diameter. Here is a macro that draws the Feret diameter.
List.setMeasurements;
x1 = List.getValue("FeretX");
y1 = List.getValue("FeretY");
length = List.getValue("Feret");
degrees = List.getValue("FeretAngle");
if (degrees>90)
degrees += 180;
angle = degrees*PI/180;
x2 = x1 + cos(angle)*length;
y2 = y1 - sin(angle)*length;
setColor("red");
Overlay.drawLine(x1, y1, x2, y2);
Overlay.show();
-wayne
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