re ex-
dation
ion in
ica-
dels
Slope
YST"
DTM,
orma-
nalyzed
netry
ita
vical
utes
in s
"m.
. Geo-
es of
utes
w line
all
pre-
10dels
"n the
type objeets definition
regular xyz coordinate triplets
int Spot Local high and low points; no assumptions on the slope of the
porn Surrounding terrain are made
objects 5
peak Specific local high z-value
pit Specific local low z-value
break A three-dimensional line which defines a change in slope or a
surface discontinuity
jsnsar drain A specific form for the breakline; this type assumes that the
Sosa surface on either side of the linear object has an increasing
254 slope. The height values increase or decrease monotonically
along the line
ridge A specific form of the breakline; this type assumes that the
surface on either side of the linear object has a decreasing
slope
contour All heigt values along the contour line are the same
double-line An area which consists of a series of planes with various slopes
drain A drainage object which at the map scale is large enough to be
represented as two short lines
ros edge It defines a boundary. Only objects inside the boundary are
ore considered as part of the model
objeets
lake It maintains a constant height value
obscure It bounds or limits the extent of a region. No restrictions are
made about the height value of any point within the interior
Table 1 Typical objects of height models
There can be additional objects or themes.
For example, a theme "verify" can contain
all check points. These points (objects)
ue
HEIGHT MODEL >
Nonas
double line drain ridge
C) : point object
— : linear object
[1 : areaobject
Pig. 2 Objects of the theme
"Height model"
can be used for the assessment of the accu-
racy of the height models. Furthermore, a
theme "slope" with the object "polygon"
and attributed with slope values can be
created. Then one can derive areas (poly-
gons) for slope classes from the height
model ( see fig. 3). In an object-oriented
height model one can create, verify, mani-
pulate, and analyze the objects as well as
the height models (see Fig. 4). The height
models can be represented as height matri-
ces (GRID), triangulated irregular networks
; slope aspect height
attributes area area area
perimeter perimeter perimeter
object (area) polygon polygon polygon
theme SLOPE ASPECT HEIGHT
Fig. 3 Topologically structured themes
of polygons derived from TIN models
(TIN) , or topologically structured con-
tours (CONTOUR). A GRID model or better
its points carry attributes such as height,
slope, grey values, etc. The CONTOUR model
(which is derived from contours) is topo-
logically structured. Its objects are
height zones (polygons) which have attri-
buts (e.g. the bounding height values,
area, etc.). From a TIN model one can de-
rive area objects (polygons) which are
attributed and topologically structured.
In TIGRIS "MODELER" all objects and height
models are part of a large design file C
ject space). This design file as well as
the program "MODELER" reside in the memory
of the computer. The objects and their
different models can therefore be edited,
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