TITLE

Geo::Geometry

Geo::Geometry

A series of classes for storing geographic data.

This module is based on chapters 8 and 9 of the Open Geospatial Consortium's OpenGISⓇ Implemantation Standard for Geographic Information - Simple Feature Access - part 1: Common architecture. This can be obtained from https://www.ogc.org/standards/sfa.

Generic Methods

The following methods are available for most classes. Classes for which they are not available are documented below.

type

The type method returns a member of the WKBGeometryType enum corresponding to the geometry type.

Str

The Str method returns a string representing the object. Note that this is not the WKT representation, which can be obtained using the wkt method described below.

wkb

The wkb method will produce a Buf object with the well-known-binary representation of the object. An optional named argument byteorder parameter is available. The value of the argument is one of the values of the WKBByteOrder enum. The default value is wkbXDR (little endian) with the alternative being wkbNDR (big endian).

wkt

The wkt method returns a string containing the well-known text representation of the geometry.

tobuf

The tobuf method is used internally; This interface may change without warning.

Subroutines

from-wkt

The from-wkt subroutine takes a string as parameter and returns a Geometry object if the string contains a WKT representation of a geometry.

from-wkb

The from-wkb subroutine takes a Buf as parameter, and returns a Geometry object if the Buf contains a WKΒ representation of a geometry.

Enums

Two enums are defined which represent values used in the WKB representation of a geometry.

WKBByteOrder

The WKBByteOrder enum gives the values used in the byte order field of a WKB representation. It contains two values wkbXDR (0, little-endian) and wkbBDR (1, big-endian).

WKBGeometryType

The WKBGeometryType enum contains the values used in the geometry type filed of a WKB representation. It allows for the following values:

Object types (classes)

Geometry

Geometry is a role which all the other objects inherit. It contains no methods, and is simply a marker that another class is a Geometry type.

If you want to check whether a variable contains any of the gemoetry classes, then code like

  if $variable ~~ Geometry { ... }

can be useful.

Point

PointZ

PointM

PointZM

The Point class represents a single point geometry. It has two attributes, x and y, each of which isconstrained to be a 64-bit floating point number (num).

The PointZ class also contains a third attribute z to represent a third dimension.

The PointM class, in addition to the X and y attributes contains an m attribute which can contain an arbitrary "measure" in addition to the two-dimensionallocation.

The PointMZ class combines the z attribute of PointZ and the m attribute of PointM.

An object of each class may be constructed either by using named parameters (Point.new(x => 10, y => 12), or by using positional parameters (PointZ.new(1,2,3)). When positional parameters are used, the ordering of the parameters is x, y, z, m; omitting those parameters which are not appropriate for the object type.

All the parameters of a point geometry are required. NaN might be used if an m parameter for example were not required.

LineString

LineStringZ

LineStringM

LineStringZM

The LineString class represents a single line, a sequence of Points, not necessarily closed.

Similarly, LineStringZ, LineStringM and LineStringZM are lines consisting of sequences of PointZs, PointMsand PointZMs respectively.

An object in the LineString family is created by passing an array of the appropriate point type geometries, to the named argument points.

At the moment there is no way of accessing the contents of a LineString geometry other than using the standard methods.

LinearRing

LinearRingZ

LinearRingM

LinearRingZM

Objects in the LinearRing classes are not normally intended for end users, apart from their use in creating more complex objects. None of the usual methods apply to these types of object.

A linear ring is similar to a line string, but is closed; i.e. the last point should be identical to the first point. This is not currently enforced, but may be in the future. Creation of a linear ring is the same as that of a line string. The ring should be simple; the path should not cross itself. This is also not enforced.

Each of these classes has a winding method. This determines whether the linear ring is clockwise (a positive number is returned) or anti-clockwise (a negative number is returned). This method will be unreliable unless the linear ring actually is a simple closed loop. The winding method ignores everything except the x and y attributes.

Polygon

PolygonZ

PolygonM

PolygonZM

A Polygon consists of one or more LinearRings. In general, the first linear ring should be clockwise (with a positive winding number). The other linear rings should be fully enclosed within the first and be disjoint from each other. They should have a negative winding number. These rings represent a polygon (the first ring) and holes within that polygon, represented by the other rings. Having only a single ring specified is acceptable (and normal under most circumstances), representing a polygon without holes.

A Polygon is created using an array of rings, such as Polygon.new(rings => @rings).

PolygonZ, PolygonM and PolygonZM behave similarly.

Triangle

TriangleZ

TriangleM

TriangleZM

A triangle is a polygon where the outer ring has exactly four points, the fourth being the same as the first and otherwise having no oints in common. The points must not be in a straight line. No internal rings are permitted.

PolyhedralSurface

PolyhedralSurfaceZ

PolyhedralSurfaceM

PolyhedralSurfaceZM

A polyhedral surface is a set of contiguous non-overlapping polygons. (There are further restrictions.)

TIN

TINZ

TINM

TINZM

A triangular irregular network is a polyhedral surface consisting only of triangles.

MultiPoint

MultiPointZ

MultiPointM

MultiPointZM

The MultiPoint classes behave just like LineStrings, including their definition. The difference is the intent of the object. A LineString, as the name implies, forms a line. A MultiPoint object is just a collection of points.

MultiLineString

MultiLineStringZ

MultiLineStringM

MultiLineStringZM

A MultiLineString object contains an array of LineStrings. It is created with that array:

     MultiLineString.new(linestrings => @array-of-linestrings)

MultiPolygon

MultiPolygonZ

MultiPolygonM

MultiPolygonZM

Just as a MultiPoint is a collections of Points, and a MultiLineString is a collection of LineStrings, a MultiPolygon is a collection of Polygons.

GeometryCollection

GeometryCollectionZ

GeometryCollectionM

GeometryCollectionZM

A GeometryCollection is an arbitrary collection of geometry objects. Unlike a PointCollection, a LineStringCollection or a PolygonCollection, the objects do not need to be of the same geometry type.