

triangles {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-con-
     straint 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', repre-
     senting 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 con-
     strained two-dimensional {Delaunay} triangulation pack-
     age.  ACM Transactions on Mathematical Software.  22,
     1-8.

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

     `tri', `print.tri', `plot.tri', `summary.tri', `trian-
     gles'

_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)

