[AstroPy] How do you create a dimensionless Cartesian coordinate?

[Leo Singer]

H Erik,

I found that:

astropy.coordinates.ICRSCoordinates(x=1, y=0, z=0)

also worked.

Leo

On Oct 23, 2013, at 10:59 AM, Erik Tollerud <erik.tollerud at gmail.com> wrote:

> You probably want this:
> 
> from astropy import units as u
> from astropy.coordinates import CartesianPoints
> cp = CartesianPoints(1, 0, 0, u.dimensionless_unscaled)
> 
> `dimensionless_unscaled` is an ordinary unit (with a string
> representation of just '', the empty string), so you just pass that in
> to indicate the units are supposed to be dimensionless. The reason
> this is necessary is that the default argument to `unit` is None, and
> None means "no unit given", rather than "dimensionless".
> 
> 
> 
> 
> On Tue, Oct 22, 2013 at 1:34 AM, Leo Singer <lsinger at caltech.edu> wrote:
>> Hello,
>> 
>> How do you create a dimensionless Cartesian coordinate? If I try the obvious way, by passing pure numbers to the constructor, I get the following exception:
>> 
>> $ python -c "import astropy.coordinates; astropy.coordinates.CartesianPoints(1, 0, 0)"
>> ERROR: UnitsError: None is not a valid Unit [astropy.coordinates.distances]
>> Traceback (most recent call last):
>>  File "<string>", line 1, in <module>
>>  File "/Users/.../local/lib/python2.7/site-packages/astropy/coordinates/distances.py", line 279, in __new__
>>    raise u.UnitsError(str(e))
>> astropy.units.core.UnitsError: None is not a valid Unit
>> 
>> This is using the latest build from master, by the way.
>> 
>> Thank you,
>> Leo Singer
>> Graduate Student @ LIGO-Caltech
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> 
> 
> 
> -- 
> Erik