Class Name: Mesh Face Table

Superclass - Data Table

Definition

A Mesh Face Table is a two dimensional Data Table that defines the face elements of a Finite Element Mesh object in terms of vertex numbers in the ordered Vertex component list of the Finite Element Mesh.

The two Axes are the Mesh Face Index Number axis and the Node Number axis. For a given Mesh Face Index Number i (>0) and Node Number j, the (i,j)-th cell gives the vertex number that comprises the j-th node of the i-th Mesh Face. The Mesh Face vertices are listed (j index) in clockwise order around the outer perimeter of the Mesh Face, starting and ending with a first vertex. If inner perimeter rings are present, the vertex list along the Node Number axis continues with inner perimeter vertices in counter clockwise order starting and ending with a first vertex on each inner ring.

The Mesh Face node ordering implicitly defines the edges of each Mesh Face. Surface topology is optionally defined by adding the adjacent Mesh Face index number as a second Table Property Description to each cell. The adjacent Mesh Face index number in cell (i,j) is the Mesh Face adjacent to Mesh Face i at the edge between nodes j and j+1.

Primary Page in DRM Diagram:

• 18

Secondary Pages in DRM Diagram:

• 6

Example

Base Vertex List: 1-6

Mesh:

        (1)-----(2)-----(3)
         \  A  /  \  B   |
          \   /  C \     |
           (4)------(5)-(6)

Mesh Face Table (without surface topology):

                    Node #
               | 1   2   3   4   5
            ------------------------
  Polygon #  1 |1  |2  |4  |1  |0  |  -->Polygon A
             2 |2  |3  |6  |5  |2  |  -->Polygon B
             3 |4  |2  |5  |4  |0  |  -->Polygon C

Each cell: vertex #

Mesh Face Table (with surface topology):

                    Node #
               | 1   2   3   4   5
            ------------------------
  Polygon #  1 |1,0|2,3|4,0|1,0|0,0|  -->Polygon A
             2 |2,0|3,0|6,0|5,3|2,0|  -->Polygon B
             3 |4,1|2,2|5,0|4,0|0,0|  -->Polygon C

Each cell: vertex #, adj_mesh_face #

FAQs

Isn't a Mesh Face Table just an instance of a Property Table?

No, a Mesh Face Table is constrained to specific Axes, Table Property Descriptions, cell data ordering, and data_table_type. Furthermore, a Mesh Face Table can only be a component of a Finite Element Mesh.

What are the Axis constraints?

There must be two Regular Axes as follows:

• First Regular Axis:
  axis_type = EDCS_AC_INDEX_TO_MESH_FACE that assigns an index value to each Mesh Face.
  axis_value_count = total number of Mesh Faces in the table.
  

• Second Regular Axis:
  axis_type = EDCS_AC_INDEX_TO_MESH_NODE
  axis_value_count = M + R,
  where M = the maximum number of nodes for any one Mesh Face in the table, and
  R = is the maximum number of perimeter rings in any one Mesh Face.
  (If all the Mesh Faces have simply connected perimeters, then R=1)

• Both Regular Axes:
  interpolation_type = SE_INTERP_DISALLOWED;
  first_value = 1;
  spacing = 1;
  values_are_ints = SE_TRUE;
  type_of_spacing = SE_LINEAR_SPACING;
  axis_alignment = SE_NOT_ALIGNED;
  axis_unit = SE_UNITS_INDEX
  

What are the Table_Property Description constraints?

The Table_Property Descriptions are:

• First Table_Property Description:
  The Vertex number in the ordered Vertex list that represents the j-th node of the i-th Mesh Face (=0 if j>#of last listed node of Mesh Face i, in other words zero fill).

  attribute_code = EDCS_AC_INDEX_TO_MESH_VERTEX

• Optional Second Table_Property Description:
  The Vertex_index_number Table_Property Description pairs (Mesh Face i, node j to node j+1) define the edges of Mesh Face i. The Adjacent_Mesh Face_index defines surface topology by indicating the table index of the Mesh Face k adjacent to Mesh Face i along this edge. A value of 0 indicates an "outside" or "universal" adjacency. A value of i for Mesh Face i indicates that the edge is artificially connecting an inside perimeter ring to another perimeter ring.

  attribute_code = EDCS_AC_INDEX_TO_ADJACENT_MESH_FACE.

• Both Table_Property Descriptions:
  value_type = SE_PDV_U_INT_32 value_unit = SE_UNITS_INDEX

What is the ordering rule for the Vertex_index_number Table Property Description?

The rule is:
For a given Mesh Face index i, the nodes j shall be listed starting from a vertex on the outside perimeter of the Mesh Face and continuing consecutively around the perimeter in clockwise direction until the first vertex is reached (and repeated). If "inside" perimeters exist, node numbering continues counter clockwise around each internal ring in similar fashion. Clockwise implies an "up" direction. If the Finite Element Mesh is a surface, then "up" should be chosen consistently across all Mesh Faces. However, if the mesh is a solid mesh, then "up" is arbitrary for each Mesh Face. (A Finite Element_Mesh is solid if a Solid_Definition_Table is a component).

What is the data_table_type constraint?

data_table_type = EDCS_CC_MESH_FACE_TABLE

Constraints

Composed of (one-way)(inherited)

• optionally, some {ordered} Image Mapping Functions

Composed of (one-way)

• exactly (2) {ordered} Regular Axis
• a bounded set of {ordered} Table Property Descriptions[1..2] (notes)

Composed of (one-way metadata)(inherited)

• optionally, an Access
• optionally, some Browse Graphics
• optionally, a Citation
• optionally, some Cross References
• optionally, a Data Quality
• optionally, a Description
• optionally, a Keywords
• optionally, a Point of Contact
• optionally, a Time Constraints Data

Component of (one-way)(inherited)

• optionally, some Property Grids

Component of (two-way)(inherited)

• optionally, a Data Table Library

Component of (two-way)

• one Finite Element Mesh

Inherited Field Elements

Notes

Composed of Notes

Table_Property_Description

 either 1 or 2 Property Descriptions

Fields Notes

data_table_type

 identifies the type of the table
 (e.g.: elevation grid (EDCS_CC_TERRAIN_ELEVATION),
        bathymetry (EDCS_CC_OCEAN_FLOOR_BATHYMETRY),
        underwater sound speed
        (EDCS_CC_OCEAN_WATER_CHARACTERISTICS_SOUND_SPEED), etc.)