/ Filters / Chapter 35. Using spatial properties of features in filters / Area and length of intersectionsThis property makes sense for intersections of area, text, image and line feature with area, text and image argument features. The intersection length is not defined for line argument features.
The length of the intersection of area, text or image tested feature with an argument feature is defined as total length of all those segments of tested feature's boundaries which are located within the argument feature. Both outer boundary of the tested feature and its inner boundaries (if any) are taken into account.
On the figure 35-1 the intersection length of feature T with feature A1 is 3 units, with feature A2 – 8 units (two segments of 4 units each), and with feature A3 – 0 units.
If the tested feature and the argument feature have coincident boundary segments, these segments are not included into the intersection length. For instance, on the figure 35-2 the intersection length of T with A1 equals 0, and the intersection length of T with A2 equals 8 (only four vertical boundary segments of T which lie within A2 are included). The intersection length of T with A3 equals 0, because there is no such boundary segment of T which lies within A3.
Figure 35-2. “Intersection Length” property for area features
It is clear that this property is not defined for line argument features because they have no inner region which would contain boundary segments of a tested feature.
In the same time, it is possibly to define the Intersection Length property for a line feature type. In this case argument features are to belong to an area, text or image type. The value of this property for a line tested feature is calculated as the length of that part of that feature which lies in inner region of the argument feature. Similarly to the previous case, the coincidence of the line feature with a boundary of the argument feature is not taken into account when evaluating their intersection length.
Examples are shown on the figure 35-3.
Figure 35-3. “Intersection Length” property for line features
On this figure the intersection length of tested feature T with the argument feature A1 is 3, with feature A2 – 3 too, and the intersection length of feature T with A3 equals 0 because there is only coincidence with the feature's boundary.
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