Full text: XVIIth ISPRS Congress (Part B4)

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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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