Cone search

[Morgan Fouesneau]

Hi Folks,

I wonder if there is a nice way to do a cone search instead of a box/rectangle selection?

I thought about the filter keyword in fetch with something like

def cone_filter(ra, dec, r, units=['deg', 'deg']):

         def fn(qresult):

                for rows in qresult:

                     _ra   = row['ra']

                     _dec = row['dec']

                     cond = sphdist( ra, dec, _ra, _dec) < r

                     #where sphdist returns the arc length between two points on the unit sphere

                     yield rows[cond]

        return fn

query = db.query('select * from table')

query.fetch( filter=cone_filter(ra,dec,r) )

However this is very not optimal because we are still looking at all the healpix cells. So that it is very inefficient

Is there a better way?

Cheers

Morgan

[Branimir Sesar]

On 10/27/2012 10:54 PM, Morgan Fouesneau wrote:
> Hi Folks,
>
> I wonder if there is a nice way to do a cone search instead of a
> box/rectangle selection?
>
> I thought about the filter keyword in fetch with something like

How about

bounds = [(lsd.bounds.beam(48.91628357, -10.41170942, 10),
lsd.bounds.intervalset((-np.inf, np.inf))]

q.fetch(bounds=bounds)

where "10" means 10 degrees and coordinates are in RA and Dec.

Brani

[Morgan Fouesneau]

Thanks! I did not saw the beam function...

[Morgan Fouesneau]

Hi, I am trying to use bounds during the fetch but I have this strange error that I do not understand. It seems to work for a while and then crashed.

The error does not show up using lsd-query script.

1 : import lsd

2 : db = lsd.DB('lsd-test/')

3 : q = db.query ('select phat_id, ra,dec, brick from phatphot')

4 : b = [lsd.bounds.rectangle(120,20,160,60), None]

5 : q.fetch(bounds)

6 : q.fetch(b)

Remote Traceback (most recent call last):

  File "/home/morgan/bin/lsd/opt/lsd/current/lib/python/lsd/pool2.py", line 81, in _worker

    for result in mapper(item, *mapper_args):

  File "/home/morgan/bin/lsd/opt/lsd/current/lib/python/lsd/table_catalog.py", line 90, in _get_cells_kernel

    for bounds_xy, bounds_t in bounds:

ValueError: need more than 1 value to unpack

Any Idea of what I do wrong?

[Morgan Fouesneau]

Nevermind, for people who did the same mistake:

b = [lsd.bounds.rectangle(120,20,160,60), None]
q.fetch( [ b ] )

On Monday, November 12, 2012 11:21:13 AM UTC-8, Morgan Fouesneau wrote:

Hi, I am trying to use bounds during the fetch but I have this strange error that I do not understand. It seems to work for a while and then crashed.

The error does not show up using lsd-query script.

1 : import lsd

2 : db = lsd.DB('lsd-test/')

3 : q = db.query ('select phat_id, ra,dec, brick from phatphot')

4 : b = [lsd.bounds.rectangle(120,20,160,60), None]

5 : q.fetch(bounds)

[Eddie Schlafly]

Yup. There is also bounds.make_canonical() for this.

e.g., q.fetch(bounds.make_canonical(bounds.rectangle(...))
I think that also handles the reverse situation, where you have only
specified a time range.