[yt-dev] [yt_analysis/yt] Cartesian coordinates broken for FLASH datasets in 3.0 (issue #528)

[John ZuHone]

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New issue 528: Cartesian coordinates broken for FLASH datasets in 3.0
https://bitbucket.org/yt_analysis/yt/issue/528/cartesian-coordinates-broken-for-flash

John ZuHone:

The coordinate fields "x", "y", and "z" are incorrect in FLASH data in 3.0. The notebook at 

https://hub.yt-project.org/nb/dwg4ew 

shows an example of this. If you grab the coordinates from the fields themselves, they are shifted by pf.domain_left_edge, but if you look at the data object's fcoords property, these coordinates are correct. 

I suspect the reason for this is that the geometry handler, which defines the coordinate fields by, e.g. (in yt.geometry.cartesian_fields.py):

```
#!python
def _coordX(field, data):
    return data.pf.domain_left_edge[0] + data.fcoords[...,0]
add_cart_field('x', function=_coordX, display_field=False)

```

But for FLASH data the fcoords property already has the correct coordinate translation, I suspect because it is getting it from the grids. This presents a quandary, because changing either the way the field is defined will likely wind up with wrong coordinates for other frontends. Any ideas, @MatthewTurk?

I haven't tried it on Enzo data, but I guess this doesn't show up in that case because (once again) domains are usually (0,1). 

Responsible: jzuhone
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