 # Foreshortening effect (tilt angle)

Hello all,
Hope you all fine and well.

I want to measure the area in some SEM images, but the images are tilted 54 degrees, so imageJ will give an incorrect measurement.
so how to fix that?
So how to avoid this effect?

Hi
@samer1985

1 Like

Hi Mathew
FeCrAl-fin.rid.06.tif (849.2 KB)
FeCrAl-fin.rid.006.tif (932.7 KB)

My answer is more mathematical than ImageJ.
1.`ImageJ

``````//setTool("freehand");
roiManager("Select", 0);
roiManager("Measure");

``````
1. The calculation that remains to be done: These are mathematics:
Projection of any triangle:
Any triangle ABC with respect to the projection plane P, which has been translated to contain point A.
The plane of the triangle makes an alpha angle with the plane P (dihedral angle).
The triangle ABC projects into AB’C '.
A polygon breaks down into triangles. Thus the area of ​​projection of a polyone follows the same law in cosine.

``````Area(AB'C') = Area(ABC) x cos (alpha)
``````

[
Indication Site of to respect copyright (In French): http://villemin.gerard.free.fr/GeomLAV/Triangle/Calcul/Projecti.htm]

Many thanks, Mathew 1 Like