What is a geometry?

Introduction

Vector data consists of geometries such as points, lines, polygons, circles, and so on. Examples of vector data are buildings, roads, railways, stations, and so on.

Geometry terminology

Curve

A curve is a continuous, one-dimensional shape. You can retrieve its points using a single parameter. A curve may consist itself of other curves, for example curve segments.

Curve segment

1-dimensional geometric object for representing a continuous component of a curve using homogeneous interpolation and definition methods. It is the simplest form of a curve.

Point

0-dimensional geometric primitive, representing a position.

Ring

A ring is a closed curve, meaning that its start and end points are the same.

Surface

A surface is a continuous, 2-dimensional shape. Its exterior boundary, which separates it from infinite space, is defined by a single ring. A surface may contain zero or more holes, all of which are also defined using rings.

Geometry model

The following sections show the hierarchy for the geometry model. The diagrams are not exhaustive.

Basis for the geometry model

Every geometry is defined with respect to a coordinate reference.

Geometries can be categorized according to their dimensions.

  • Point: 0-dimensional geometry

  • Curve: 1-dimensional geometry

  • Surface: 2-dimensional geometry

  • Solid: 3-dimensional geometry (not included in the diagram)

Geometry model basis

Curves

The diagram shows the hierarchy for the curve geometries.

Geometry model curves

Surfaces

Surface terminology:

Patch

A patch is a surface based on a single ring, thus not having any holes.

CompositePatch

A composite patch is a general surface that is based on an exterior patch and zero or more inner patches. The inner patches represent holes within the surface. The patch rings should not intersect.

The diagram shows the hierarchy for the surface geometries.

Geometry model surfaces

Geometry aggregates

The diagram shows the hierarchy for aggregates of geometries.

Geometry model aggregates

Common geometries

You have access to the following commonly used geometries. For each of the geometries, there is a link to the factory method to create the geometry.

Point

A single point location. See GeometryFactory::createPoint.

Line

A line defined by exactly 2 points. See GeometryFactory::createLine.

Polyline

A line defined by multiple points.

ILcdPolyline
Figure 1. Polyline
PolylineRing

A line defined by multiple points representing a ring; thus the start and the end point are always the same.

ILcdPolygon
Figure 2. Polyline ring
Circle

All of its points are located on a circle with a center point and a radius.

ILcdCircle
Figure 3. Circle

A circle can be defined in two ways:

Circular arc

All of its points are located on a circle with a center point and a radius. The arc starts at a start angle and ends at an end angle.

ILcdCircularArc
Figure 4. Circular arc

A circular arc can be defined in three ways:

Ellipse

All of its points are located on an ellipse defined by a center point, semi-major axis length, semi-minor axis length and a rotation angle.

ILcdEllipse
Figure 5. Ellipse

An ellipse can be created using GeometryFactory::createEllipse.

Elliptical arc

All of its points are located on an ellipse with a center point, semi-major axis, semi-minor axis and a rotation angle. The arc starts at a start angle and ends at an end angle.

ILcdArc
Figure 6. Elliptical arc
Arc band

All of its points are located on the band with a minimum radius and a maximum radius from the focus point. The arc band starts at a start angle and ends at an end angle.

ILcdArcBand
Figure 7. Arc band

See link:../../../../reference/LuciadCPillar/luciad::GeometryFactory::createArcBand [GeometryFactory::createArcBand].

Bounds

A box with a location (Point), a width, a height, and a depth. Bounds is often used as a bounding box for more complex geometries.

ILcdBounds
Figure 8. Bounds
Patch

A patch is a surface with an exterior is based on a ring. It has no holes.

CompositePatch

A composite patch is a surface based on an exterior patch and zero or more interior patches. The patch rings do not intersect.

Polygon

A polygon is a surface which has an exterior and 0 or more interiors, which represent holes. The exterior and the interior boundaries are closed polyline geometries (polyline ring).

ILcdComplexPolygon
Figure 9. Polygon
Extruded geometry

An extruded geometry is a 3D shape created by extruding a 2D Curve or Surface with a minimum and maximum height. Currently, all Curve or Surface instances are supported bases for an extruded geometry, as well as any MultiGeometry that consists solely of such geometries. The image below shows an extruded ellipse.

extruded handles
Figure 10. Extruded geometry
Multi geometry

A multi-geometry is a collection of one or more geometry objects.