Cancelling, stretching or clipping a 3D electrode.

Cancelling the data on an electrode:

An electrode can be cancelled (that is, ignored) by putting 0 subdivisions (but see cancelling electrode data).

Stretching or squashing an electrode:

See note on stretching.

Selected segments can be manually removed from any type of electrode.

Clipping an electrode:

A whole electrode (that is, a sphere, cylinder, cone or disc) can be 'clipped' (that is, limited, truncated or cropped, so that part of it is removed). Other types of electrode cannot be clipped.

The user is asked to give the number N of clipping planes (maximum 6), followed by N sets of further information about the clipping planes. These planes are defined by the equation

a*x + b*y + c*z > d

if the plane is a 'minimum' plane, or the equation

a*x + b*y + c*z < d

if the plane is a 'maximum' plane.

For example to remove all segments that have x greater than 2, use the maximum plane

1*x + 0*y + 0*z < 2

Then only segments that have x < 2 will be retained, for any values of y and z.

The user specifies whether the plane is a minimum or maximum plane, and the values of a, b, c and d.

The electrode will be subdivided in the usual way, and then any segment that has any of its corners outside the limits will be removed (before Aug 2007 the coordinates of the middle of the segment were used). The edges defined by the remaining segments may then be ragged. When one or planes of reflection symmetry exist the program will usually apply the clipping planes to segments in the 'minimum sector'. A problem might exist (very rarely) when x = y is a plane of symmetry and the user wants to clip in the x and y directions, and it might be necessary then to change the sign or order of the clipping coordinates. The use of this option is illustrated in the ‘shape’ files shap3d08 and shap3d11 and in the ‘example’ files xmpl3d01 and xmpl3d02.

For users who are editing or constructing an 'input data file' without the use of the data-builder -that is, pre-processor:

But Manual editing is certainly not recommended -it is a relic from the time when the databuilder was not available All users are strongly encouraged to use the databuilder, which always gives the correct formats and which has many options for which the formats are not described or easily deduced.

The option is triggered by making the first subdivision number negative.

You must then enter a line that gives the number N of clipping planes (maximum 6), followed by N lines. There are two choices of format for these lines:

(1) If the clipping is simple, such as x > a, then put 'xmin' in the first 4 spaces of the line, followed on the same line by the value of a. Similarly for 'xmax', ymin', 'ymax', etc.

(2) If the clipping plane slopes then the clipping condition has a form such as:

a*x + b*y + c*z > d

In this case the line starts with 'min ', followed by the 4 numbers a, b, c and d in the remaining spaces. If the condition is:

a*x + b*y + c*z < d

then the line starts with 'max '.

If an electrode is both stretched and clipped, the stretching data should be given first.