DTM Representation 
  
Once DTM information has been collected, it may be repre- 
sented in a variety of compressed or non-compressed formats. 
The terms format, representation, and structure are used 
interchangeably here. Keep in mind that most DTM produc- 
tion systems today collect only elevation information, 
either as discrete spot heights or line profiles.  DTM's, 
however, may be represented by elevations, contours, 
tessellated polygons, surface polynomials, fractal numbers, 
slope maps, power spectra, convolved displays, etc. Each 
representation is some approximation to the data collected, 
and is done to satisfy the storage and input requirements 
of the DTM user. | 
ACCURACY CONSIDERATIONS 
  
The term accuracy related to DTM's means many things to 
different people. It would be appropriate to define 
accuracy in terms of geomorphological quality, precision 
of information, positional accuracy, data commonality, data 
compatibility, and compression (representation). 
Geomorphological Quality 
  
The geomorphological quality of a DTM is the degree to 
which the DTM represents the actual landform. This concept 
is extremely difficult to define quantitatively. It con- 
siders all of the statistically measurable quantities of 
the DTM as well as the visually apparent anomalies, texture, 
and fit to the actual landform.  Forstner (19835) presents 
a good discussion on sampling interval and form of data 
collected on the quality of a DTM. He presents evidence 
that demonstrates that slope and curvature information are 
extremely important in the quality of a DTM. Note however 
that most DTM production systems do not collect this in- 
formation. 
Faintich et. al. (1982) demonstrate that variations in 
production such as different types of equipment, source 
scale and type, etc., produce a variety of textures and 
anomalies in DTM's when the pieces are assembled over large 
cells of data. Although such DTM's may meet numerical 
accuracy requirements, the overall quality of the DTM is 
affected by the non-uniform appearance. 
Precision of Information 
  
  
  
  
  
  
  
  
  
  
   
  
   
  
  
  
  
   
   
  
  
  
  
  
   
  
  
  
  
  
   
  
  
  
  
   
  
  
   
The precision of the data described by a DTM is a statistical 
representation of the primarily random error or noise in 
the model. Precision is generally determined by statistical