def get_links(args):
this_nite, q = args
'''
The key routine for building the linkmap. Examines all points in this_nite and identifies points in
exposures within look_ahead_nites of this_nite with separation consistent with parallax motion of a distant
solar system object.
'''
this_nites_expnums = np.unique(df_nites[this_nite]['expnum'].values)
link_nites = [nite for nite in nites if 0<nites_between(this_nite, nite)<=look_ahead_nites]
# Compute parallax offsets from each exposure in current nite to the target nites
print 'Processing nite: ', this_nite
print ' Nite contains', len(df_nites[this_nite]),' points in ', len(this_nites_expnums), ' exposures'
print ' ', len(link_nites),' nites available for linking'
linkmap_nite = {}
for exp in this_nites_expnums:
exposure = df_exps.loc[df_exps['expnum']==exp]
exp_ra, exp_dec = hours(exposure['ra'].values[0]), degrees(exposure['dec'].values[0])
exp_date = date(exposure['date'].values[0])
lon, lat = Ecliptic(Equatorial(exp_ra, exp_dec)).get()
this_dlon, this_dlat, this_vlon, this_vlat = linkutils.parallax(exp_ra, exp_dec, exp_date)
this_exps_points = df_nites[this_nite].loc[df_nites[this_nite]['expnum']==exp] # points in this exposure
this_exps_points.index = range(len(this_exps_points)) # reindex starting from zero
this_exps_objids = this_exps_points['objid'].values # objids in this exposure
linkmap_exp = dict(zip(this_exps_objids, [[] for i in range(len(this_exps_objids))]))
for next_nite in link_nites:
deltaT = nites_between(this_nite, next_nite)
next_dlon, next_dlat, next_vlon, next_vlat = linkutils.parallax(exp_ra, exp_dec, exp_date+deltaT)
dlon, dlat = next_dlon-this_dlon, next_dlat-this_dlat
search_center = Equatorial(Ecliptic(lon+dlon/nominal_distance, lat+dlat/nominal_distance))
deltaR = np.sqrt(dlon**2*np.cos(lat)**2 + dlat**2)/nominal_distance
offset_ra, offset_dec = hours(search_center.ra - exp_ra), degrees(search_center.dec - exp_dec)
shifted_points = apply_offset(this_exps_points, offset_ra, offset_dec) # apply parallax offset
this_exps_tree = build_kdtree(shifted_points) # make KDtree from the shifted points
near_list = this_exps_tree.query_ball_tree(trees[next_nite], deltaR)
for ipoint in range(len(near_list)):
if near_list[ipoint] != []:
point1 = this_exps_points.iloc[ipoint]
for jpoint in near_list[ipoint]:
point2 = df_nites[next_nite].iloc[jpoint]
if tno_like(point1, point2):
objid1 = point1['objid']
objid2 = point2['objid']
linkmap_exp[objid1].append(objid2)
linkmap_nite.update(linkmap_exp)
q.put(this_nite)
return linkmap_nite
def tno_like(point1, point2, vmax=150, debug=False):
#
# vmax is max velocity in arsec/day
#
lon1, lat1 = Ecliptic(Equatorial(point1['ra'], point1['dec'])).get()
lon2, lat2 = Ecliptic(Equatorial(point2['ra'], point2['dec'])).get()
displacement = separation((lon2, lat2), (lon1, lat1))
displacement_asec = displacement*180/np.pi*3600
if point2['date'] != point1['date']:
velocity = displacement_asec/(point2['date'] - point1['date'])
else:
velocity=9999
this_dlon, this_dlat, this_vlon, this_vlat = linkutils.parallax(point1['ra'], point1['dec'], point1['date'])
next_dlon, next_dlat, next_vlon, next_vlat = linkutils.parallax(point2['ra'], point2['dec'], point2['date'])
dlon, dlat = next_dlon-this_dlon, next_dlat-this_dlat
dot = np.cos(lat1)**2*(lon2 - lon1)*dlon + (lat2 - lat1)*dlat
norm = np.sqrt(np.cos(lat1)**2*dlon**2 + dlat**2)
cosine = dot/(norm*displacement)
TNOlike = True if velocity<vmax and cosine>cosine_cut(displacement_asec) else False
return TNOlike
def tno_like(self, point1, point2, debug=False):
lon1, lat1 = Ecliptic(Equatorial(point1.ra, point1.dec)).get()
lon2, lat2 = Ecliptic(Equatorial(point2.ra, point2.dec)).get()
displacement = ephem.separation((lon2, lat2), (lon1, lat1))
displacement_asec = displacement*180/np.pi*3600
if point2.date != point1.date:
velocity = displacement_asec/(point2.date - point1.date)
else:
velocity=9999
this_dlon, this_dlat, this_vlon, this_vlat = linkutils.parallax(point1.ra, point1.dec, point1.date)
next_dlon, next_dlat, next_vlon, next_vlat = linkutils.parallax(point2.ra, point2.dec, point2.date)
dlon, dlat = next_dlon-this_dlon, next_dlat-this_dlat
dot = np.cos(lat1)**2*(lon2 - lon1)*dlon + (lat2 - lat1)*dlat
norm = np.sqrt(np.cos(lat1)**2*dlon**2 + dlat**2)
cosine = dot/(norm*displacement)
TNOlike = True if velocity<self.vmax and cosine>self.cosine_cut(displacement_asec) else False
if debug:
linkinfo = {'v':velocity, 'cos':cosine, 'dot':dot, 'displacement':displacement_asec, 'cut':self.cosine_cut(displacement_asec),
'point1':point1, 'point2':point2, 'lon1':lon1, 'lon2':lon2, 'lat1':lat1, 'lat2':lat2, 'dlon':dlon, 'dlat':dlat, 'norm':norm,
'TNOlike':TNOlike}
self.linkpoints.append(linkinfo)
return TNOlike
def link_obj(self, point, verbose=False):
nites = self.nites
thisnite = point.nite
if verbose: print 'Linking point ', point.objid, point.date, thisnite, point.ra, point.dec, point.band
look_ahead_nites = sorted([n for n in nites if 0<self.nites_between(thisnite,n)<self.look_ahead_nights])
lon, lat = Ecliptic(Equatorial(point.ra, point.dec)).get()
# this_dlon, this_dlat = self.para[point.expnum]['dlon'], self.para[point.expnum]['dlat']
this_dlon, this_dlat, this_vlon, this_vlat = linkutils.parallax(point.ra, point.dec, point.date)
next_obj = []
for next_nite in look_ahead_nites:
if verbose: print 'Linking target nite: ', next_nite
deltaT = self.nites_between(thisnite,next_nite)
next_dlon, next_dlat, next_vlon, next_vlat = linkutils.parallax(point.ra, point.dec, point.date+deltaT)
dlon, dlat = next_dlon-this_dlon, next_dlat-this_dlat
search_center = Equatorial(Ecliptic(lon+dlon/self.nominal_distance, lat+dlat/self.nominal_distance))
deltaR = np.sqrt(dlon**2*np.cos(lat)**2 + dlat**2)/self.nominal_distance
# print ephem.separation((search_center.ra, search_center.dec), (point.ra, point.dec))*3600*180/np.pi/deltaT
sep_max = self.vmax*np.pi/(180*3600)*(deltaT)/2
current_objects = [obj for obj in self.objects if obj.nite == next_nite \
and (self.bands is None or obj.band in self.bands) \
and ephem.separation((search_center.ra, search_center.dec), (obj.ra, obj.dec))<deltaR]
if verbose: print ' Found ', len(current_objects), ' points in search window'
# now the real work: for each object, test to see
# if it's consistent with being the next point in
# a KBO trajectory, i.e. consistent in direction and displacement with earth parallax.
if True:
for point2 in current_objects:
if verbose: print 'Examining point ', point2.objid, point2.date, thisnite, point2.ra, point2.dec, point.band, ' ... ',
# next_dlon, next_dlat = self.para[point2.expnum]['dlon'], self.para[point2.expnum]['dlat']
# dlon, dlat = next_dlon-this_dlon, next_dlat-this_dlat
# if self.tno_like(point, point2, lon, lat, dlon, dlat, debug=True):
if self.tno_like(point, point2, debug=False):
if verbose: print 'Point is tno_like...'
next_obj.append(point2)
else:
if verbose: print 'Point NOT tno_like...'
return next_obj
