Encyclopaedia Index

### Coordinate points, fixing of

(see FIXCOR real, Group 6)

### Coordinate systems

PHOENICS is capable of representing fluid-flow phenomena by reference to: Cartesian grids, cylindrical-polar grids and general curvilinear (ie BFC) grids.

However, the orientation of the plot is defined by the cartesian axes X, Y and Z in Euclidean space. These reference axes are displayed at the bottom right of the screen. You can change the orientation of these axes.

### COORDINATES

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Three different coordinate systems may be used by PHOTON, which are:

1. The position and orientation of the plot are defined in cartesian (X,Y,Z) space, and are shown by the axes plotted at the lower left of the plot. You can change the orientation of the plot using the VIEW and UP commands.
2. The location of quantities within the solution domain is defined in terms of grid-coordinate space (I,J,K). For non-BFC cases the (I,J,K) axes will coincide with (X,Y,Z), but for BFC cases the curvilinear nature of the grid may mean that (I,J,K) bears a complex relationship to the cartesian axes. You specify grid locations using (I,J,K), e.g. GRID I 1, GRID K 7.
3. Cells are numbered in terms of an (IX,IY,IZ) coordinate system, so that IX=1 represents the first cell in the I direction, IZ=4 the fourth cell in the K direction, and so on. Since PHOENICS variables are calculated for cell centres, the VECTOR and CONTOUR commands use the cell-centre notation, i.e. VEC IX 1.

Right-handed and left-handed coordinate systems may be used. The default is right-handed, and the commands RHAND and LHAND are used to switch between the two.