OGC简单要素数据标准：架构与应用详解

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representation, and open version of the same classes may be used in other circumstances, such as topological

representations.

Geometry

+ dimension() : Integer

+ coordinateDimension() : Integer

+ spatialDimension() : Integer

+ geometry Ty pe() : String

+ SRID() : Integer

+ envelope() : Geometry

+ asText() : String

+ asBinary () : Binary

+ isEmpty () : Boolean

+ isSimple() : Boolean

+ is3D() : Boolean

+ isMeasured()() : Boolean

+ boundary () : Geometry

query

+ equals(another :Geometry ) : Boolean

+ disjoint(another :Geometry ) : Boolean

+ intersects(another :Geometry ) : Boolean

+ touches(another :Geometry ) : Boolean

+ crosses(another :Geometry ) : Boolean

+ within(another :Geometry ) : Boolean

+ contains(another :Geometry ) : Boolean

+ ov erlaps(another :Geometry ) : Boolean

+ relate(another :Geometry , matrix :String) : Boolean

+ locateAlong(mValue :Double) : Geometry

+ locateBetween(mStart :Double, mEnd :Double) : Geometry

analy sis

+ distance(another :Geometry ) : Distance

+ buf f er(distance :Distance) : Geometry

+ conv exHull() : Geometry

+ intersection(another :Geometry ) : Geometry

+ union(another :Geometry ) : Geometry

+ dif f erence(another :Geometry ) : Geometry

+ sy mDif f erence(another :Geometry ) : Geometry

ReferenceSystems::

MeasureReferenceSystem

ReferenceSystems::

SpatialReferenceSystem

«interf ace»

ReferenceSystems::ReferenceSystem

{abstract}

+ dimension() : Integer

+ axisName() : String[]

+mesureRS

0..1

«realize»

+spatialRS

Figure 2: Geometry class operations

6.1.2.2 Basic methods on geometric objects

⎯ Dimension ( ): Integer — The inherent dimension of this geometric object, which must be less than or equal

to the coordinate dimension. In non-homogeneous collections, this will return the largest topological

dimension of the contained objects.

⎯ GeometryType ( ): String — Returns the name of the instantiable subtype of Geometry of which this

geometric object is an instantiable member. The name of the subtype of Geometry is returned as a string.

⎯ SRID ( ): Integer — Returns the Spatial Reference System ID for this geometric object. This will normally be a

foreign key to an index of reference systems stored in either the same or some other datastore.

⎯ Envelope ( ): Geometry — The minimum bounding box for this Geometry, returned as a Geometry. The

polygon is defined by the corner points of the bounding box [(MINX, MINY), (MAXX, MINY), (MAXX, MAXY),

(MINX, MAXY), (MINX, MINY)]. Minimums for Z and M may be added. The simplest representation of an

Envelope is as two direct positions, one containing all the minimums, and another all the maximums. In some

cases, this coordinate will be outside the range of validity for the Spatial Reference System.

⎯ AsText ( ): String — Exports this geometric object to a specific Well-known Text Representation of Geometry.

⎯ AsBinary ( ): Binary — Exports this geometric object to a specific Well-known Binary Representation of

Geometry.

⎯ IsEmpty ( ): Integer — Returns 1 (TRUE) if this geometric object is the empty Geometry. If true, then this

geometric object represents the empty point set ∅ for the coordinate space. The return type is integer, but is

interpreted as Boolean, TRUE=1, FALSE=0.

⎯ IsSimple ( ): Integer — Returns 1 (TRUE) if this geometric object has no anomalous geometric points, such

as self intersection or self tangency. The description of each instantiable geometric class will include the

specific conditions that cause an instance of that class to be classified as not simple. The return type is

integer, but is interpreted as Boolean, TRUE=1, FALSE=0.

⎯ Is3D ( ): Integer — Returns 1 (TRUE) if this geometric object has z coordinate values.

⎯ IsMeasured ( ): Integer — Returns 1 (TRUE) if this geometric object has m coordinate values.

⎯ Boundary ( ): Geometry — Returns the closure of the combinatorial boundary of this geometric object

(Reference [1], section 3.12.2). Because the result of this function is a closure, and hence topologically

closed, the resulting boundary can be represented using representational Geometry primitives (Reference [1],

section 3.12.2). The return type is integer, but is interpreted as Boolean, TRUE=1, FALSE=0.

6.1.2.3 Methods for testing spatial relations between geometric objects

The methods in this subclause are defined and described in more detail following the description of the sub-types

of Geometry. For each of the following, the return type is integer, but is interpreted as Boolean, TRUE=1,

FALSE=0.

⎯ Equals (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object is “spatially

equal” to anotherGeometry.

⎯ Disjoint (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object is “spatially

disjoint” from anotherGeometry.

⎯ Intersects (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object “spatially

intersects” anotherGeometry.

⎯ Touches (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object “spatially

touches” anotherGeometry.

⎯ Crosses (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object “spatially

crosses’ anotherGeometry.

⎯ Within (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object is “spatially within”

anotherGeometry.

⎯ Contains (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object “spatially

contains” anotherGeometry.

XVII

⎯ Overlaps (anotherGeometry: Geometry): Integer — Returns 1 (TRUE) if this geometric object “spatially

overlaps” anotherGeometry.

⎯ Relate (anotherGeometry: Geometry, intersectionPatternMatrix: String): Integer — Returns 1 (TRUE) if this

geometric object is spatially related to anotherGeometry by testing for intersections between the interior,

boundary and exterior of the two geometric objects as specified by the values in the intersectionPatternMatrix.

This returns FALSE if all the tested intersections are empty except exterior (this) intersect exterior (another).

⎯ LocateAlong (mValue: Double): Geometry — Returns a derived geometry collection value that matches the

specified m coordinate value. See Subclause 6.1.2.6 “Measures on Geometry” for more details.

⎯ LocateBetween (mStart: Double, mEnd: Double): Geometry — Returns a derived geometry collection value

that matches the specified range of m coordinate values inclusively. See Subclause 6.1.2.6 “Measures on

Geometry” for more details.

6.1.2.4 Methods that support spatial analysis

All of the following are geometric analysis and depend on the accuracy of the coordinate representations and the

limitations of linear interpolation in this standard. The accuracy of the result at a fine level will be limited by these

and related issues.

⎯ Distance (anotherGeometry: Geometry):Double — Returns the shortest distance between any two Points in

the two geometric objects as calculated in the spatial reference system of this geometric object. Because the

geometries are closed, it is possible to find a point on each geometric object involved, such that the distance

between these 2 points is the returned distance between their geometric objects.

⎯ Buffer (distance: Double): Geometry — Returns a geometric object that represents all Points whose distance

from this geometric object is less than or equal to distance. Calculations are in the spatial reference system of

this geometric object. Because of the limitations of linear interpolation, there will often be some relatively

small error in this distance, but it should be near the resolution of the coordinates used.

⎯ ConvexHull ( ): Geometry — Returns a geometric object that represents the convex hull of this geometric

object. Convex hulls, being dependent on straight lines, can be accurately represented in linear interpolations

for any geometry restricted to linear interpolations.

⎯ Intersection (anotherGeometry: Geometry): Geometry — Returns a geometric object that represents the

Point set intersection of this geometric object with anotherGeometry.

⎯ Union (anotherGeometry: Geometry): Geometry — Returns a geometric object that represents the Point set

union of this geometric object with anotherGeometry.

⎯ Difference (anotherGeometry: Geometry): Geometry — Returns a geometric object that represents the Point

set difference of this geometric object with anotherGeometry.

⎯ SymDifference (anotherGeometry: Geometry): Geometry — Returns a geometric object that represents the

Point set symmetric difference of this geometric object with anotherGeometry.

6.1.2.5 Use of Z and M coordinate values

A Point value may include a z coordinate value. The z coordinate value traditionally represents the third

dimension (i.e. 3D). In a Geographic Information System (GIS) this may be height above or below sea level. For

example: A map might have point identifying the position of a mountain peak by its location on the earth, with the

x and y coordinate values, and the height of the mountain, with the z coordinate value.

A Point value may include an m coordinate value. The m coordinate value allows the application environment to

associate some measure with the point values. For example: A stream network may be modeled as multilinestring

value with the m coordinate values measuring the distance from the mouth of stream. The method

LocateBetween may be used to find all the parts of the stream that are between, for example, 10 and 12

kilometers from the mouth. There are no constraints on the m coordinate values in a Geometry (e.g., the m

coordinate values do not have to be continually increasing along a LineString value).

Observer methods returning Point values include z and m coordinate values when they are present.

Spatial operations work in the "map geometry" of the data and will therefore not reflect z or m values in

calculations (e.g., Equals, Length) or in generation of new geometry values (e.g., Buffer, ConvexHull, Intersection).

This is done by projecting the geometric objects onto the horizontal plane to obtain a "footprint" or "shadow" of the

objects for the purposed of map calculations. In other words, it is possible to store and obtain z (and m)

coordinate values but they are ignored in all

other operations which are based on map geometries.

Implementations are free to include true 3D geometric operations, but should be consistent with ISO 19107..

6.1.2.6 Measures on Geometry

The LocateAlong and LocateBetween methods derive MultiPoint or MultiCurve values from the given geometry

that match a measure or a specific range of measures from the start measure to the end measure. The

LocateAlong method is a variation of the LocateBetween method where the start measure and end measure are

equal. (See SQL/MM [1])

6.1.2.6.1 Empty Sets

A null value is returned for empty sets.

6.1.2.6.2 Geometry values without m coordinate values.

An empty set of type Point is returned for geometry values without m coordinate values.

6.1.2.6.3 Zero-dimensional geometry values

Only points in the 0-dimensional geometry values with m coordinate values between SM and EM inclusively are

returned as multipoint value. If no matching m coordinate values are found, then an empty set of type Point is

returned.

For example:

a) If LocateAlong is invoked with an M value of 4 on a MultiPoint value with well-known text

representation:

multipoint m(1 0 4, 1 1 1, 1 2 2, 3 1 4, 5 3 4)

then the result is the following MultiPoint value with well-known text representation:

multipoint m(1 0 4, 3 1 4, 5 3 4)

b) If LocateBetween is invoked with an SM value of 2 and an EM value of 4 on a MultiPoint value with

well-known text representation:

multipoint m(1 0 4, 1 1 1, 1 2 2, 3 1 4, 5 3 5, 9 5 3, 7 6 7)

then the result is the following MultiPoint value with well-known text representation:

multipoint m(1 0 4, 1 2 2, 3 1 4, 9 5 3)

c) If LocateBetween is invoked with an SM value of 1 and an EM value of 4 on a Point value with well-

known text representation:

point m(7 6 7)

XIX

then the result is the following MultiPoint value with well-known text representation:

point m empty

d) If LocateBetween is invoked with an SM value of 7 and an EM value of 7 on a Point value with well-

known text representation:

point m(7 6 7)

then the result is the following MultiPoint value with well-known text representation:

multipoint m(7 6 7)

6.1.2.6.4 One-dimensional geometry value

Interpolation is used to determine any points on the 1-dimensional geometry with an m coordinate value between

mStart and mEnd inclusively. The implementation-defined interpolation algorithm is used to estimate values

between measured values, usually using a mathematical function. The interpolation is within a Curve element and

not across Curve elements in a MultiCurve. For example, given a measure of 6 and a 2-point LineString where the

m coordinate value of start point is 4 and the m coordinate value of the end point is 8, since 6 is halfway between

4 and 8, the interpolation algorithm would be a point on the LineString halfway between the start and end points.

The results are produced in a geometry collection. If there are consecutive points in the 1-dimensional geometry

with an m coordinate value between mStart and mEnd inclusively, then a curve value element is added to the

geometry collection to represent the curve elements between these consecutive points. Any disconnected points

in the 1-dimensional geometry values with m coordinate values between mStart and mEnd inclusively are also

added to the geometry collection. If no matching m coordinate values are found, then an empty set of type

ST_Point is returned.

For example:

a) If LocateAlong is invoked with an M value of 4 on a LineString value with well-known text

representation:

LineStringM(1 0 0, 3 1 4, 5 3 4, 5 5 1, 5 6 4, 7 8 4, 9 9 0)

then the result is the following MultiLineString value with well-known text representation:

MultiLineStringM((3 1 4, 5 3 4), (5 6 4, 7 8 4))

b) If LocateBetween is invoked with an mStart value of 2 and an mend value of 4 on a LineString value

with well-known text representation:

LineStringM(1 0 0, 1 1 1, 1 2 2, 3 1 3, 5 3 4, 9 5 5, 7 6 6)

then the result is the following MultiLineString value with well-known text representation:

MultiLineStringM((1 2 2, 3 1 3, 5 3 4))

c) If LocateBetween is invoked with an SM value of 6 and an EM value of 9 on a LineString value with

well-known text representation:

LineStringM(1 0 0, 1 1 1, 1 2 2, 3 1 3, 5 3 4, 9 5 5, 7 6 6)

then the result is the following MultiPoint value with well-known text representation:

MultiPointM(7 6 6)

d) If LocateBetween is invoked with an SM value of 2 and an EM value of 4 on a MultiLineString value

with well-known text representation:

MultiLineStringM((1 0 0, 1 1 1, 1 2 2, 3 1 3), (4 5 3, 5 3 4, 9 5 5, 7 6 6))

then the result is the following MultiLineString value with well-known text representation:

MultiLineStringM((1 2 2, 3 1 3),(4 5 3, 5 3 4))

e) If LocateBetween is invoked with an SM value of 1 and an EM value of 3 on a LineString value with

well-known text representation:

LineStringM(0 0 0, 2 2 2, 4 4 4)

then the result may be the following MultiLineString value with well-known text representation:

MultiLineStringM((1 1 1, 2 2 2, 3 3 3))

f) If LocateBetween is invoked with an SM value of 7 and an EM value of 9 on a MultiLineString value

with well-known text representation:

MultiLineStringM((1 0 0, 1 1 1, 1 2 2, 3 1 3), (4 5 3, 5 3 4, 9 5 5, 7 6 6))

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