[yt-users] Units for camera.draw_line

[Nathan Goldbaum]

Hi Sean,

Can you try again with:

cam.draw_line(im, [2e8,0.,0.]*ds.length_unit, [0.,2e8,0.]*ds.length_unit)

It looks like this function was never properly updated for yt-3.0.  What's
happening is that the camera's origin vector is a YTArray, but the second
and third argument of the draw_line function are specified in that
function's docstrings as ndarrays.  When the draw_line function tries to
compute the difference between camera.origin and [2e8, 0, 0], it throws a
unit error (as it should) since camera.origin has units of code_length
(which is the same as centimeters for your FLASH simulation), but x0 is
unitless.

We should probably add some code to the draw_line function so that if a
user passes in a list or ndarray rather than a YTArray, we cast x0 and x1
to be YTArrays in code_length units.  This would be a super simple initial
contribution to yt, if you're up for it.

-Nathan

On Mon, Dec 29, 2014 at 2:07 PM, Sean Couch <smc at tapir.caltech.edu> wrote:

> Hi yt-users,
>
> Newb question:  I’m trying to draw a line on my volume render of some
> FLASH data using camera.draw_line but I’m getting an error.  My guess is
> that it is something to do with units, but I can’t figure out how to fix
> what I’m doing.  I’m assuming that draw_line using code units, which for
> FLASH should be cgs.  Here is my code snippet:
>
>
> cam = ds.camera(c, L, W, N, transfer_function=tf, ds=ds, no_ghost=True,
>                 fields=field, log_fields=[False])
> im = cam.snapshot()
>
> cam.draw_coordinate_vectors(im)
> cam.draw_domain(im)
> cam.draw_line(im, [2e8,0.,0.], [0.,2e8,0.])
>
> And here is the error I get when I run it:
>
> Traceback (most recent call last):
>   File "render_radv.py", line 53, in <module>
>     cam.draw_line(im, [2e8,0.,0.], [0.,2e8,0.])
>   File
> "/work/00863/smc/yt-x86_64/src/yt-hg/yt/visualization/volume_rendering/camera.py",
> line 415, in draw_lin\
> e
>     dx0 = ((x0-self.origin)*self.orienter.unit_vectors[1]).sum()
>   File "/work/00863/smc/yt-x86_64/src/yt-hg/yt/units/yt_array.py", line
> 716, in __rsub__
>     lo = sanitize_units_add(self, left_object, "subtraction")
>   File "/work/00863/smc/yt-x86_64/src/yt-hg/yt/units/yt_array.py", line
> 134, in sanitize_units_add
>     raise YTUnitOperationError(op_string, inp.units, dimensionless)
> yt.utilities.exceptions.YTUnitOperationError: The subtraction operator for
> YTArrays with units (code_length) an\
> d (1) is not well defined.
>
> Any help or guidance would be much appreciated!
>
> Thanks,
> Sean
>
>
>
> -----------------------------------------------------------
> Sean M. Couch
> Theoretical Astrophysics Including Relativity
> California Institute of Technology
> Mail Code 350-17
> Pasadena, CA  91125
> (626) 395-4282
> www.tapir.caltech.edu/~smc
>
>
> _______________________________________________
> yt-users mailing list
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>
>
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