Display of Crystal Axes
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Dialog Box - called from: Input2 Menu

Either of two types of axes may be drawn, Movable and Corner axes. Movable axes may be located anywhere in the drawing with the Displacement parameters - these parameters are in structure coordinates (Angstroms). The arms of the axial cross are two-ended, showing both position and negative ends. Corner axes are placed in a fixed position (in screen or drawing coordinates, inches or centimeters) relative to one of the corners of the drawing. They show only one arm of each axis, which is oriented as far as possible toward the interior of the drawing.

In the 3D display mode, the axes can be either lines or cylinders with the specified radius (which can also be set in the General sub-option of the 3D Parameters command in the Input2 menu). The axes are not shown in Stereopairs in 2D Drawing modes since they do not have a definite location in space, but they are shown in stereopairs in the 3D Drawing mode

The Scale factor refers to the distance from the center to either end (one end for corner axes). Thus a scale factor of 0.5 gives lines equal in total length to the axes. In 2D Drawing modes, the axes are always shown in front of the atoms and faces.

The Labels, if selected, will be on the positive ends of the axes for movable axes.

Use PostScript font. This allows you to enter a character string for PostScript fonts supported by a PostScript printer if such fonts do not appear in the standard system font dialog called up by the Font button. This character string usually specifies the weight (normal, bold) and slant (italic, oblique) of the font, but not the size, which is specified in the Font dialog. Certain PostScript typefaces are standard, and should be present on most PostScript printers.

Movable axis settings.

If the Dashed box is checked, the c axis is shown solid, the b axis is dashed with the dash length and interval set in the Preferences dialog in the Settings menu or the Crystal Edges dialog in the Input2 menu, and the a axis is dashed with half these intervals.

If the One-ended box is checked, only the positive ends of the axes will be shown, otherwise both ends will be shown.

If the Include in scaling box is checked the axes will not go off-scale in either the Universal or Maximize for each view scaling modes (Scaling dialog, Input2 menu).

The Displacements can be used to separate the structure and axes. Note that you can also move the structure with the Centering and Displacements command in the Input2 menu. The Scale Grid can assist in these displacements. In 3D display mode, the axes may interpenetrate with the structure, and the x-coordinate or front-back displacement is also relevant. Unlike the Unit Cell, the crystal axes are not fixed with respect to the structure, rather their location is specified in observer coordinates (see Coordinate Systems), with respect to the center of the structure.

Clicking in the plot area after clicking on the Locate with Mouse button will determine the y and z (across and up) coordinates, all that is required in 2D Drawing modes; in 3D Drawing mode the x (front-back) coordinate will be unchanged and can be set independently.

Projection - Orthographic/Perspective. If Perspective (Input2 menu) is off, the axes are always projected by the orthographic method, in the same way as the structure. If Perspective is on, the projection point is always on a perpendicular to the projection plane (screen or paper) passing through the approximate center of the structure. If the Perspective radio button in this group is chosen, the axes are projected from the same point, as a three-dimensional object. This means that if the axes are displaced from the center of the structure, they are viewed obliquely, and it may not be obvious that they are in parallel orientation with the structure. This can be confusing to the observer who is not aware of the complexities of perspective projection. If the Orthographic radio button is selected, the axial cross is projected orthographically, which usually is more satisfactory. If the axes are at or near the center of the structure, there is little or no difference between the two methods.

Corner axis settings.

The axes may be located in any of the four corners, at the specified Displacement in both directions from the corner. If the title is printed at the bottom, the displacement will be from the title instead of the corner.

In Perspective projection, corner axes are always drawn as for the Orthographic projection option for movable axes, above. This means essentially that they indicate the orientation at the center of the drawing, not that of
their actual position.