negative centroid values

Posted by Gwen Barnes on Jul 19, 2006; 8:02pm
URL: http://imagej.273.s1.nabble.com/negative-centroid-values-tp3702087.html

Hi folks,

I'm trying to find the centroid of a circular object, but I sometimes get
negative (!) values for X or Y.

I outline it with the polygon tool, under "set measurements" I chose area,
centroid, and feret's diameter, and then I select "analyze, measure."  Most
of the time this works fine.  However, if I encompass too large an area, I
get negative values for either X or Y of the centroid.  My image is a 41 M
tiff, 2552 pixels wide by 4200 pixels high.  My latest results from
"measure" were:

area: 1210035
X:    1357.474
Y:    -1649.551
diam:    1343.317

Whereas the actual values should be about:

X:  1344
Y:  1944
diam: 1308

In this case, maybe the Y value is the only incorrect one, but since there's
no way the answer could be negative, it makes me distrust all the values.

Is anyone else familiar with this problem, and does anyone have suggestions
for getting the right answer?  Thanks.

-Gwen

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