Hi Nathan,

This is just a guess, but do you really mean to be taking the square root of R cross V, at line 30? That quantity could potentially be negative, depending on the sense in which the fluid is spinning.

-Andrew Myers

On Tue, Sep 6, 2011 at 5:54 PM, Nathan Goldbaum <goldbaum@ucolick.org> wrote:

Hello all,

Right now I'm trying to generate maps of the Toomre Q in an isolated galaxy simulation.  To do so, I'm using yt to generate maps of the gas column density as well as density-weighted projections of the sound speed and orbital frequency, which I'm using as a proxy for the epicyclic frequency.

Unfortunately, I'm having some trouble making projected maps of the orbital frequency.  I've defined two new derived fields, CylinderRadius and AngularVelocity (http://paste.yt-project.org/show/1784/).

When I try to project the AngularVelocity field, I get what looks like garbage: http://i.imgur.com/PkYhe.png

However, slices work just fine: http://i.imgur.com/NnEbq.png

I've written the derived fields in a coordinate-dependent way, since I'll always be doing projections down a fixed axis.  Is that where my problem lies?  My understanding of how yt does projections is too shallow to figure out exactly what's going wrong here, so I'm hoping the collective wisdom of the yt developers and user base can come to the rescue.

Best regards,

Nathan Goldbaum
Graduate Student
Astronomy & Astrophysics, UCSC
goldbaum@ucolick.org
http://www.ucolick.org/~goldbaum

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