triangles              package:tripack              R Documentation

_E_x_t_r_a_c_t _a _l_i_s_t _o_f _t_r_i_a_n_g_l_e _f_r_o_m _a _t_r_i_a_n_g_u_l_a_t_i_o_n _o_b_j_e_c_t

_D_e_s_c_r_i_p_t_i_o_n:

     This function extracts a triangulation data structure from an
     triangulation object created by `tri.mesh'.

     The vertices in the returned matrix (let's denote it  with
     `retval') are ordered counterclockwise with the first vertex taken
     to be the one with smallest index.  Thus, `retval[i,"node2"]' and
     `retval[i,"node3"]' are larger than `retval[i,"node3"]' and index
     adjacent neighbors of node `retval[i,"node1"]'. The columns `trx'
     and `arcx', x=1,2,3 index the triangle and arc, respectively,
     which are opposite (not shared by) node `nodex', with `trix'= 0 if
     `arcx' indexes a boundary arc.  Vertex indexes range from 1 to N,
     triangle indexes from 0 to NT, and, if included, arc indexes from
     1 to NA = NT+N-1.  The triangles are  ordered on first (smallest)
     vertex indexes, except that the sets of constraint triangles
     (triangles contained in the closure of a constraint region) follow
     the non-constraint triangles.

_U_s_a_g_e:

     triangles(tri.obj)

_A_r_g_u_m_e_n_t_s:

 tri.obj: object of class `"tri"'

_V_a_l_u_e:

     A matrix with columns `node1',`node2',`node3', representing the
     vertex nodal indexes, `tr1',`tr2',`tr3', representing neighboring
     triangle indexes and `arc1',`arc2',`arc3' reresenting arc indexes.

     Each row represents one triangle.

_A_u_t_h_o_r(_s):

     A. Gebhardt

_R_e_f_e_r_e_n_c_e_s:

     R. J. Renka (1996). Algorithm 751: TRIPACK: a constrained
     two-dimensional {Delaunay} triangulation package. ACM Transactions
     on Mathematical Software. 22, 1-8.

_S_e_e _A_l_s_o:

     `tri', `print.tri', `plot.tri', `summary.tri', `triangles'

_E_x_a_m_p_l_e_s:

     # we will use the test data from library(akima):
     library(akima)
     data(akima)
     akima.tr<-tri.mesh(akima$x,akima$y)
     triangles(akima.tr)

