COLLAPSE

 

Collapse polygons into centerlines.  Only polygons less then a specified width will be collapsed.  Connectivity with a specified line coverage is maintained.

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COLLAPSE <in_poly_cover> <in_line_cover> <out_poly_cover> <out_line_cover> <in_item> <out_item> <remap_table> {min_length} {max_width} {cellsize} {weed_tolerance} {spline_tolerance} {dangle_length} {fuzzy_tolerance}

 

ARGUMENTS

 

<in_poly_cover> - the input polygon coverage whose polygons are to be collapsed into centerlines.

 

<in_line_cover> - the input line coverage whose lines are connected to the polygons in the <in_poly_cover>.

 

The connectivity between the these lines and the collapsed polygons will be maintained.

 

<out_poly_cover> - the name for the output polygon coverage.

 

This coverage contains polygons, or parts thereof, that were not collapsed.

 

WARNING - The boundaries of the output polygons will be generalized and will not exactly match the boundaries of the input polygons.  The smaller the {cellsize}, the better the match.

 

WARNING - The output polygon boundaries are also written to the <out_line_cover>.  At this time the boundaries in these two coverages will not always match exactly.  Deviation occurs where the <out_line_cover> boundaries are snapped to <in_line_cover> arcs to maintain connectivity.

 

<out_line_cover> - the name for the output line coverage.

 

This coverage contains the collapsed centerlines and the boundaries of polygons, or parts thereof, that were not collapsed.

 

The collapsed centerlines are attributed using the <remap_table>.

 

The attribute of each collapsed centerlines is stored in an item named <out_item> with a `1' suffix, e.g. CFF1.  The attribute of each polygon boundary is also stored in an item named <out_item> with a `1' suffix.  In the event that a polygon boundary is shared by adjacent polygon, the second attribute is stored in an item named <out_item> with a `2' suffix, e.g. CFF2.

 

WARNING - The centerlines will not always fall inside of the original polygon boundaries.  The smaller the {cellsize}, the less likely it is that the centerlines will not fall inside of the original boundary.

 

WARNING - The boundaries of the output polygons will be generalized and will not exactly match the boundaries of the input polygons.  The smaller the {cellsize}, the better the match.

 

WARNING - The output polygon boundaries are also written to the <out_poly_cover>.  At this time the boundaries in these two coverages will not always match exactly.  Deviation occurs where the <out_line_cover> boundaries are snapped to <in_line_cover> arcs to maintain connectivity.

 

<in_item> - the input item in the <in_poly_cover> PAT that identifies the type of each polygon, e.g. CFF code.

 

<out_item> - the name for the output item in the <out_poly_cover> PAT.

 

This named is also used as the prefix for two items in the <out_line_cover> AAT.  The suffixes are `1' and `2', e.g. CFF1 and CFF2.  These items contain the attribute of the polygons on each side of the boundary.

 

<remap_table> - the input INFO table that defines attribute changes between <in_item> and the <out_item> when polygons have been collapsed.

 

The <in_item> values must be stored in an item named OLD, and the new values for the <out_item> must be stored in an items named NEW.

 

{min_length} - the minimum length of the polygons that are to be collapsed.

 

WARNING - This option is not be implemented yet.

 

{max_width} - the maximum width of polygons (or sections thereof) that are to be collapsed.

 

Any place where polygons are narrower than the {max_width}, the polygon will be collapsed into a centerline, providing that the {min_length} requirement has been met.

 

{cellsize} - the size of the grid cells used to do the processing.

 

COLLAPSE converts the <poly_cover> into a temporary grid in order to determine where to collapse the polygons.

 

If no {cellsize} is specified, it defaults to 1/1000 of the maximum dimension of the BND of the <in_poly_cover>.

 

{weed_tolerance} - the weed tolerance used during generalization of polygon centerlines and boundaries.

 

If not specified it defaults to the {cellsize}.

 

{spline_tolerance} - the initial GRAIN size used during generalization of polygon centerlines and boundaries.

 

If not specified it defaults to zero.

 

If the {spline_tolerance} equals zero, then no splining takes place.

 

{dangle_length} - the minimum allowable dangle length for the <out_line_cover>.

 

Dangles less than this length will be deleted.  Dangles are created where there are polygon lobes but no attachment to arcs in the <in_line_cover>, e.g. inlets in a water body with no stream attached to the inlet.

 

If not specified it defaults to the {max_width}.

 

{fuzzy_tolerance} - the fuzzy tolerance for the output coverages.

 

If not specified it defaults to the fuzzy tolerance of the <in_poly_cover>.

 

 

NOTES

 

COLLAPSE runs from the ARC module of ArcInfo.

 

COLLAPSE uses four C programs that have been compiled for both Win2K and IBM AIX UNIX machines.

 

 

EXAMPLES

 

Arc: &run collapse usage

Usage: COLLAPSE <in_poly_cover> <in_line_cover> <out_poly_cover> <out_line_cover> <in_item> <out_item> <remap_table> {min_length} {max_width} {cellsize} {weed_tolerance} {spline_tolerance} {dangle_length} {fuzzy_tolerance}

 

1)  To collapse double-line streams less than 80 meters wide, using a 3- meter cell size:

 

Arc: &run collapse stream_poly stream_line stream_poly2 stream_line2 ~

Arc: cff cff cffcodes_remap # 80 3

 

cffcodes_remap is the remap table.  It's contents are:

 

Record         OLD        NEW

1         403       7901

2         419        416

3         420        417

4         422        417

5         406        405