12 Copyright © 2006 Open Geospatial Consortium, Inc. All Rights Reserved.
4.17 linear referencing system
linear positioning system positioning system that measures distance from a reference point along a route feature
NOTE The system includes the complete set of procedures for determining and retaining a record of specific points along a linear feature such as the location reference methods together with the procedures for
storing, maintaining, and retrieving location information about points and segments on the highways. [NCHRP Synthesis 21, 1974]
[ISO 19133]
4.18 point
topological 0-dimensional
geometric primitive 4.15, representing a position
NOTE The boundary of a point is the empty set. [ISO 19107]
4.19 simple feature
feature with all geometric attributes described piecewise by straight line or planar interpolation between sets of points
Note Interpolation is used on curves and surfaces, which by their nature are an infinite set of points and thus
not suitable to finite exhaustive representations. Each such geometric entity is decomposed into parts which can be expressed locally as parametric, linear combinations of control points. This is described at
length in ISO 19107.
For curves, each part called a segment in ISO 19107 has two control points P the “start point” and P
1
the “end point”. Any other P on the segment can be described using a real number parameter t between 0.0 and 1.0 in the “vector” equation:
1
1 P
tP t P
= + −
. For surfaces, each part called a “patch” in ISO 19107 can be viewed as a polygon which can be broken
into triangles each with three control points P , P
1
and P
2
. Any other P in the triangle can be described using 3 non-negative real numbers whose sum is 1.0 called “barycentric coordinates”
, , ; , ,
0; 1.0
a b c a b c
a b c ∈
+ + = ¡
in the vector equation:
2 1
cP bP
aP P
+ +
=
.
4.20 start point
first
point 4.17 of a curve 4.7
[ISO 19107]
4.21 surface
topological 2-dimensional
geometric primitive 4.15, locally representing a continuous image of a region of a
plane NOTE The boundary of a surface is the set of oriented, closed curves that delineate the limits of the surface.
[adapted from ISO 19107]
Copyright © 2006 Open Geospatial Consortium, Inc. All Rights Reserved. 13
5 Symbols and Abbreviations
Kategori