PolyLine
A PolyLine is an ordered set of vertices that consists of one or more parts. A part is a connected sequence of two or more points. Parts may be connected to and may intersect one another.
Because this specification does not forbid consecutive points with identical coordinates, shapefile readers must handle such cases. On the other hand, the degenerate zero length parts that might result are not allowed.
The
following fields are for a PolyLine:
- Box
- The bounding box for the PolyLine, stored in the order Xmin, Ymin, Xmax, Ymax
- NumParts
- The number of parts in the PolyLine
- NumPoints
- The total number of points for all parts
- Parts
- An array of length NumParts. Stores, for each PolyLine, the index
of its first point in the points array
Array indexes are numbered with respect to 0.
- Points
- An array of length NumPoints
The points for each part in the PolyLine are stored end to end. The points for part 2 follow the points for part 1, and so on. The parts array holds the array index of the starting point for each part. There is no delimiter in the points array between parts.
The following table shows PolyLine byte stream contents.
| Position | Field | Value | Type | Number | Byte order |
|---|---|---|---|---|---|
| Byte 0 | Shape Type | 3 | Integer | 1 | Little endian |
| Byte 4 | Box | Box | Double | 4 | Little endian |
| Byte 36 | NumParts | NumParts | Integer | 1 | Little endian |
| Byte 40 | NumPoints | NumPoints | Integer | 1 | Little endian |
| Byte 44 | Parts | Parts | Integer | NumParts | Little endian |
| Byte X | Points | Points | Point | NumPoints | Little endian |
Tip: X = 44 + (4 * NumParts)