#!/usr/bin/env python3
import numpy as np
from matplotlib.tri import Triangulation

def split_quads(elnode=None):
    '''
    Split quad elements to triangles and append additional elements to element table
    This script can be made much faster by using vector operation instead of the for-loop;
    just append additional elements to the end.
    '''
    if elnode is None:
        raise Exception('elnode should be a numpy array of (np,4)')

    elnode = np.ma.masked_values(elnode, -1)
    if elnode.shape[1] == 4:
        eid = np.nonzero(~((np.isnan(elnode[:,-1]))|(elnode[:,-1]<0)))[0]
        elnode = np.r_[elnode[:,:3], np.c_[elnode[eid, 0][:, None], elnode[eid, 2:]]]
    return elnode.astype('int')

def triangulation(lon, lat, tris):
    if tris.max() >= len(lon): 
        tris -= 1
    return Triangulation(lon, lat, tris)