Operations

(zoidlist) Filt(zoids, lexpr)
This function is rather specialized. First, the trapezoids passed by the handle in the first argument are separated into groups of mutually-connected trapezoids. Each group is like a wire net. We throw out the groups that do not intersect with nonzero area the dark area implied by the layer expression second argument. The return value is a handle to a list of the trapezoids that remain.

(zoidlist) GeomAnd(zoids1 [, zoids2])
This function takes either one or two arguments, each of which is taken as a zoidlist after possible conversion as described in the text for this section. If one argument is given, the return is a zoidlist consisting of the intersection regions between zoids in the argument list. If two arguments are given, the return is a list of intersecting regions between the two argument lists.

(zoidlist) GeomAndNot(zoids1, zoids2)
This function takes two arguments, each of which is taken as a zoidlist after possible conversion as described in the text for this section. The return is a list of regions covered by the first list that are not covered by the second.

(zoidlist) GeomCat(zoids1 [, ...])
This function takes one or more arguments, each of which is taken as a zoidlist after possible conversion as described in the text for this section. The return is a list of all regions from each of the arguments. There is no attempt to clip or merge the returned list.

(zoidlist) GeomNot(zoids)
This function takes one argument, which is taken as a zoidlist after possible conversion as described in the text for this section. The return is a list of zoids representing the areas of the reference area not covered by the argument list.

(zoidlist) GeomOr(zoids1, ...)
This function takes one or more arguments, each of which is taken as a zoidlist after possible conversion as described in the text for this section. The return is a list of all regions from each of the arguments, merged and clipped so that no elements overlap.

(zoidlist) GeomXor(zoids1 [, zoids2])
This function takes one or two arguments, each of which is taken as a zoidlist after possible conversion as described in the text for this section. If one argument is given, the return is a list of areas where one and only one zoid from the argument has coverage (note that this is not exclusive-or, in spite of the function name). If two arguments are given, the return is the exclusive-or of the two lists, i.e., the areas covered by either list but not both.