Cameron Manual

Chapter 8: View Direction Control

: 8.1: BASIC CONTROL; 8.2: ORIENTATION COMMANDS; 8.3: Other related commands; 8.4: PHOTOGRAPHS

One of the most important features of a graphics package is the ease with which a required molecular view can be obtained. CAMERON contains a large number of options which allow the user to control the view direction.

8.1: BASIC CONTROL

Five commands are available to control the view direction by applying rotations to the molecule. These rotations are applied cumulatively - rotating about the x axis by 20 degrees then by -10 degrees will result in an overall rotation of 10 degrees RELATIVE to the STARTING POINT.

XROT

This command is used to apply a rotation of n degrees about the x-axis which lies horizontally across the screen. The syntax is :-

XROT n

YROT

ZROT

These two commands are identical to XROT except for the axis about which the rotation is carried out. The y-axis lies vertically up the screen and the z-axis is perpendicular to the screen.

ROT

This command is a 'shorthand' for the previous three commands as it allows you to apply three successive rotations by entering only one command. The syntax is :-

ROT x y z

Note that the order of rotation is - rotate about x then y then z. The order of rotation is important - YROT 10 XROT 5 ZROT 15 will NOT produce the same result as ROT 5 10 15 as the rotation matrices are non-commutative.

CURSOR

This command allows the user to control rotation with the cursor keys. Each time a key is struck a rotation of 5 degrees is applied about the relevant axes. After each key stroke the molecule is rotated and then re-drawn. To speed up this process the molecule is drawn in line style during the CURSOR rotation and is not scaled. The set-up prior to CURSOR is restored once rotation is terminated. The keys used are :-

Rotation about the x-axis

Positive      up arrow
Negative      down arrow

Rotation about the y-axis

Positive      left arrow
Negative      right arrow

Rotation about the z-axis

Positive      Delete key (PC)
Negative      End key (PC)

Any other key stroke will terminate the CURSOR control and draw the resultant picture.

8.2: ORIENTATION COMMANDS

More specific orientation of the molecule can be achieved by relating the view direction to the position of certain atoms within the picture.

PLANE

In some cases it is useful to be able to define a PLANE and then set the view direction to be perpendicular to it. The syntax of this command is :-

PLANE at1 at2 at3 ...

At least 3 atoms must be used to define the plane (element names will not be accepted). If more than 3 are used then the program calculates the best plane through the atoms and projects onto this.

ALL PLANE ALL will generated a 'best view' of the current structure.

FACE

Alternatively you may want to view onto a particular crystallographic face of the unit cell. The syntax for this command is :-

FACE h k l

where h k and l are the miller indices of the FACE in question.

ALONG

It is possible to define the view direction as that looking down an interatomic direction. The direction is specified by inputting :-

ALONG at1 at2

As with PLANE atoms not elements must be used as the arguments. Note that the view direction is calculated as that looking down the at1 - at2 direction ie at1 is the closest of the two. The reverse view will be obtained by requesting ALONG at2 at1. ALONG also has a sub-command associated with it:-

AXIS

It is possible to define the view direction as looking along a particular unit cell axis. The syntax of the command is :-

ALONG AXIS x

where x is A, B or C.

VERTICAL

HORIZONTAL

These two commands are similar to along except that the at1 - at2 direction is oriented up (VERTICAL) or across (HORIZONTAL) the screen as required.

AXIS

The AXIS sub command may be applied to the HORIZONTAL and VERTICAL commands. This rotates the diagram around the z axis so that the required axis is HORIZONTAL or VERTICAL as specified. This is particularly useful when generating hard copy output.

BISECT

This command requires three arguments at1 at2 and at3. It will generate a view direction looking along the bisector of the at1-at2-at3 angle. The syntax is :-

BISECT at1 at2 at3

where at2 is the apex atom.

8.3: Other related commands

VIEW

The 'title' command of this group of commands is VIEW. This requires no arguments as causes a picture to be output to the current output device (see SCREEN). The picture is generated according to all of the parameters that are set up prior to its use. For example :-

XROT 10 VIEW

will rotate the molecule by 10 degrees about x and then draw a picture.

VIEW XROT 10

would draw the picture first and then carry out the rotation. This rotation would not be observed until the next VIEW is entered.

COPY

COPY is the equivalent command for hardcopy output. COPY must be followed by a filename to which the output will be send. HARDCOPY must have been used prior to this to specify the output type. The filename may be one that has already been used in the current run of CAMERON in which case the user is given an option to append the information.

MATRIX
This command allows the user to save the current view matrix.

FILE This is followed by a filename. If the file exists (and it is of the correct format) then any matrices contained within it are available and any matrices stored are appended to the file.

STORE This stores the current matrix. It is followed by a piece of text (in quotes "text") to act as a description for the matrix. On storage a number is assigned to the matrix which can be used to retrieve it later.

RETRIEVE This command obtains a view matrix from the file set up with MATRIX FILE. This command must be followed by the number of the matrix required. Note that these matrices depend on the unit cell parameters and are specific to a particular structure. They may be used for other structures but this will have very strange results. It this happens an operation such as ALONG AXIS C will recalculate a correct matrix.

LIST This outputs a list of the descriptions and numbers of the matrices currently stored.

STEREO
This generates output in the form of stereo pairs.

DEGREE The angle of rotation between the stereo pairs is given by using the DEGREE command.

NOSTEREO
Reverts output back to normal.

8.4: PHOTOGRAPHS

PHOTO

ON

OFF These commands are used to control the PHOTO facility. VIEW displays the user with information about the current scale and displays the mouse cursor once it has finished. PHOTO ON turns off this and waits for a key press before proceeding. This allows the user to obtain a 'clean' screen for photographs to be taken.

Related commands : SCREEN, HARDCOPY