def transform_pq(tspecs,matches):
    p = []
    q = []
    p_transf = []
    q_transf = []
    tids = []
    for ts in tspecs:
        tids.append(np.array([x.tileId for x in ts]))
    tsp_ind0=0
    tsp_ind1=1
    if len(tspecs)==1:
        #montage
        tsp_ind1=0

    for match in matches:
        #cycle through each item, find and apply the appropriate transforms
        sind0 = np.argwhere(tids[tsp_ind0]==match['pId'])
        sind1 = np.argwhere(tids[tsp_ind1]==match['qId'])
        if (len(sind0)>0) & (len(sind1)>0):
            sind0 = sind0[0][0]
            sind1 = sind1[0][0]
            ip = np.flipud(np.rot90(np.array(match['matches']['p'])))
            iq = np.flipud(np.rot90(np.array(match['matches']['q'])))

            ip_transf = tspecs[tsp_ind0][sind0].tforms[-1].tform(ip)
            iq_transf = tspecs[tsp_ind1][sind1].tforms[-1].tform(iq)

            p.append(ip)
            q.append(iq)
            p_transf.append(ip_transf)
            q_transf.append(iq_transf)

    return [p,q,p_transf,q_transf]

self.p,self.q,self.p_transf,self.q_transf = transform_pq(tspecs,matches)
self.xy_ave = [0.5*(p+q) for p,q in zip(self.p_transf,self.q_transf)]
self.xy_diff = [(p-q) for p,q in zip(self.p_transf,self.q_transf)]
self.rss = [np.sqrt(np.power(x[:,0],2.0)+np.power(x[:,1],2.0)) for x in self.xy_diff]