Calculate Bounds

In order to speed-up GIS analyses, such as the calculation of nearest features to a point or polygon, or point in polygon (e.g. determining the Flinn-Engdahl region of an earthquake) and polygon in polygon (e.g. determining the plant to which a plant unit belongs) comparisons, the system uses pre-calculated rectangular bounds of polygon features. In general, such bounds are not available in the original polygon feature data; hence, they should be calculated manually. The "Calculate Bounds" tool is provided to facilitate this task and calculates the bounds automatically.

The tool lists database tables that include polygon boundary data and offers two actions, either the cal-culation of bounds from polygon boundary data, or the calculation and optimization of bounds and boundaries simultaneously. The first action takes polygon boundary data as-is and calculates bounds for each polygon. If a polygon is a complex polygon comprised of multiple parts (i.e. islands), bounds are calculated separately for each part. The second action first examines boundary data of each polygon and determines the polygon parts that can be grouped to decrease the total number of bounds for each polygon. Polygon boundary data is updated in the database to reflect the optimized part groups and then bounds are calculated. For both actions, the calculated bounds are stored in the corresponding field of the selected database table. If the table does not include a bounds field, it can be created auto-matically by checking "Add bounds column if not existing" checkbox. Similarly, for records without a polygon boundary data, existing bounds data can be cleared by checking the "Clear bounds if boundary is empty" item (Figure 2).