Arc_length
Geometric functions arc_length
- arc_length(arc_poly_dataitem, valuesunit of coordinate system)
arc_length(arc_poly_dataitem, valuesunit) calculates the length of an arc or the outline of a polygon data item arc_poly_dataitem.
The resulting values unit is configured as second argument. This gives an interpretation to the resulting values. It does not convert them. For example, if the coordinate system is in meters, then the resulting output are meter, but you should also configure it to be interpreted as meters. If you want kilometers as output, you'll have to manually convert it to km.
Furthermore, note that multi-linestrings are sequences of points that contain values as separators between linestrings and that arc-length returns for any point sequence that contains one or more values. For multi-linestring, use the function mls_length
The definition of the outline of a polygon is only equal to the perimeter if the polygon has no islands and lakes.
In case a polygon consits of multiple rings, the outline also contains the artificial lines needed to relate the rings, see polygon data model.
If you want to calculate the perimeter, use a split_polygon function first to make different polygons for all exterior rings (the outline of the lakes are still a part of the calculated arc_length).
- arc or polygon data item arc_poly_dataitem with fpoint or dpoint value type and composition type arc or polygon.
attribute<meter> road_length (Road) := arc_length(road/geometry, meter);
| road/geometry | road_length |
|---|---|
| {2 {399246, 112631}{398599, 111866}} | 1001.92 |
| {3 {398599, 111866}{399495, 111924} {401801,111524}} | 3238.31 |
| {2 {401529, 114921}{398584, 114823} | 2946.63 |
domain Road, nr of rows = 3
