POLYBL.SML

This sample script illustrates the use of some of the
vector and database functions in SML. It is designed to operate
on a vector object containing contiguous polygons that might
represent countries, states, counties, census blocks, etc.  The script
selects four specific polygons by attribute, and computes
the total length of the polygon boundary lines that are not
shared between the selected polygons.  For a block of contiguous 
polgyons, this is the perimeter of the block. If none of the
selected polygons are contiguous, the calculated length 
is the total boundary length of the selected polygons.

The checks for the class of adjacent polygons require explicit 
database table.field references which must be provided for the
the particular vector object being used.  This example uses the
vector object 'states' in the UNTDSTAT.RVC Project File in the
USA sample data collection. 

Polygons are selected by the name of the state, which is contained
in the STATE_NAME field in the 'states' database table.
The line list for a selected polygon is accessed, and database
references are used to check the class assignments for the polygons
on either side of each line.  If either polygon is not among the
selected set of states, the line length is added to a perimeter
variable for the polygon. 

For each selected polygon, the SML script outputs the following
data for each unshared boundary line: line element number, 
the state to the left and right sides, and the line length.
The summed unshared boundary length is then reported for the polygon.
When all selected polygons have been processed, the total unshared
boundary length for the selected set is reported.  The in-depth
report facilitates checking that the polygon adjacency selection
criteria are working correctly.

Output information is printed to the console window, and written
to a text file.

AUTHOR: Randy Smith, MicroImages, Inc.
CREATION DATE: May 13, 1997