PolygonLib is a software library for quick clipping operations on 2D polygons and polygon sets. It is especially optimized for efficient storing great amount (> 10 million) of polygons in RAM and operations on large polygon sets.

• A portable C++ library with much optimized performance and memory utilization.
• A COM library that provides COM wrappers for objects of the C++ library. The wrappers are obtained from pools and only for objects referenced by the client, thus minimizing the COM overhead.

The library can be used in various kinds of applications (CAD, GIS, modeling systems, graphics editors, etc.) written in C++, C#, Pascal, VB and other languages allowing use of COM. It is already used in the FEFLOW modeling system and the FDAT project.

• A polygon can have several disjoint areas and holes.
• Automatic splitting of self-intersecting boundaries.
• The node based model of polygons (no duplicated vertices) is maintained automatically thus reducing the size of the used memory.
• Spatial queries (for polygons, edges and nodes) that are optimized per built-in spatial indices (B-tree for nodes and R-tree for polygons) that are maintained automatically.
• Clipping operations on polygons:
• Boolean operations (intersection, union, subtraction) on polygons and polygon sets.
• Join of two polygon sets: union, whose result is represented by maximal count of not overlapping polygons (the overlaps and the results of their subtraction from other polygons).
• Union of a polygon set (see the second screenshot).
• The numerical robustness (avoiding extraneous vertices) of the operations is achieved without inserting intersection points into original polygons.

• Much optimized memory utilization (see the test results below)
• Built-in spatial indices
• Much optimized performance of Boolean operations on polygons with large number of vertices (see the test results below)
• Very optimized Boolean operations on polygon sets (see the test results below)
• High-quality API

We have compared the performance and memory utilization of the COM version of PolygonLib with those of 2 well known polygon clipping libraries. The testing was performed on a PC with Intel Core 2 (2 GHz) CPU and 2 GB of RAM under Windows XP. The results are listed in the following table and show clear advantages of PolygonLib over the competing products (the best results are marked bold in the table).

Library	Memory use, MB		Duration of operations on polygons depending on total number of vertices, ms								Operations on polygon sets, s
	15000 geog. areas	Mesh of 199000 triangles
			Few intersections				Many intersections (most vertices)				Small sets1	Large sets2
			100	103	104	105	100	103	104	105
PolygonLib	18,3	17,4	0,21	2,0	11	92	0,22	2,3	25	300	1,2	21
PolyBoolean, C++	29,0	44,8	0,74	8,5	53	560	0,35	5,3	44	390	7,4	250
GPC, COM	43,2	57,0	0,23	3,7	91	1800	0,07	1,3	25	1200	19*	550*

¹ A mesh of 42000 triangles and a set of 2100 geographical areas.
² A mesh of 199000 triangles and a set of 15000 geographical areas.
* A polygon set can be defined in GPC only as a polygon with many boundaries.

The polygons used in the testing are contained in the archive of the evaluation version of the product (see below).

You can download the evaluation version of PolygonLib here.

• A Windows application for testing main possibilities of the C++ library. It allows loading polygon sets from .shp files, their visualization and operations on them (see the screenshots above).
• Test polygon data as .shp files.
• The evaluation version of the COM library. Please note that it has some important restrictions vs. the corresponding full version (see the readme.txt file for details).