4.9.5. Cell and Node Properties
[4.9. Grids]

Properties can be specified for the grid, the cells, or the corners (mesh values). These properties are created using the methodology described in section 4.7. The following functions are used to open the property groups associated with a grid. After finishing, the group ids must be closed using the function xfCloseGroup.

C/C++

int xfGetGridPropertyGroup(xid GridGroupId, xid *PropGroupId);
int xfGetGridCellPropertyGroup(xid GridGroupId, xid *PropGroupId);
int xfGetGridNodePropertyGroup(xid GridGroupId, xid *PropGroupId);

FORTRAN

SUBROUTINE  XF_GET_GRID_PROPERTY_GROUP(GridGroupId, PropGroupId, Error)
INTEGER(XID), INTENT(IN) :: GroupId
INTEGER(XID), INTENT(OUT):: PropGroupId
INTEGER, INTENT(OUT)     :: Error
 
SUBROUTINE  XF_GET_GRID_CELL_PROPERTY_GROUP(GridGroupId, PropGroupId, Error)
INTEGER(XID), INTENT(IN) :: GroupId
INTEGER(XID), INTENT(OUT):: PropGroupId
INTEGER, INTENT(OUT)     :: Error
 
SUBROUTINE  XF_GET_GRID_NODE_PROPERTY_GROUP(GridGroupId, PropGroupId, Error)
INTEGER(XID), INTENT(IN) :: GroupId
INTEGER(XID), INTENT(OUT):: PropGroupId
INTEGER, INTENT(OUT)     :: Error

Activity Flags

One of the reserved property names is activity. This is an array of on/off values that must be the same size as the number of cells in the grid. The activity array indicates whether every cell is on or off (included in the grid computations). If no activity flags are specified, it will be assumed that all cells are on. Activity can also be defined on a data set level for cells that are computationally active but are inactive at specific times. This occurs in hydraulic studies where grid cells are allowed to go dry (inactive).

Null Values

Curvilinear grids may have large sections of inactive space. This is especially true in riverine applications. In these cases it is often easier to build the grid without including data in the empty spaces. Sometimes elevation data is unavailable for areas outside the active portions of the grid. Empty areas can be filled in with a null value rather than cell boundary locations. When a null value is used it is stored as a property of the grid. Figure 9 shows a situation where a NULL value may be useful. The grid shown is of a river that branches. For this problem the NULL value would be used above and below the right branch of the river (everything greater than 3 in the I direction and not between 2 and 5 in the J direction).

Figure 9 2D curvilinear grid that branches.