# Elliptical blob definition?

Hi,

In the Blob picker, there are two options - circular and elliptical blob - which can be selected either individually or at the same time. The first of these is self explanatory - it is presumably searching using a gaussian disk. I have two questions re the elliptical blob:

1. How is the elliptical blob generated? Is it just an ellipse with major and minor axes from the max/min particle diameters? Or are several blobs generated by creating a 3D ellipsoid and projecting in evenly spaced directions (this would make more sense to me, for elongated particles that will have a â€śtopâ€ť and â€śsideâ€ť view).

2. What happens when both circular and elliptical blob are selected? Are both tried sequentially and the results combined? Is a circular template just used in addition to the elliptical one?

Cheers
Oli

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Hi @olibclarke,

1. Yes, itâ€™s an ellipse with major and minor axes from the min/max particle diameters that were given. Projecting a 3D ellipse would probably be a bit better, but combining circular and elliptical blobs (see 2) is an approximation to that.
2. Combining the circular and elliptical blobs means that both types are used, similarly to using multiple templates in the template picker - particles that match either shape sufficiently well are picked (after local non-max suppression and distance constraints).

Hope that helps!

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Thanks Ali, all makes sense.

Looking at the log files I can see what it does now - it generates three circular blobs, with diameters, ranging from the min to the max, and a single elliptical blob with the minor axis as the min diameter and the major axis as the max diameter.

I wonder if a better way to go might be just to only use an elliptical blob, but with all possible combos of the min/max/middle dimensions for the major and minor axes. This would give 6 templates with varying degrees of both size and ellipticity, ranging from circular to very elongated, and might better represent the range of views one sees for an elongated particle.

Cheers, Oli