ca- 
heory 
other 
am in 
odel. 
ng as 
here 
eters 
other 
dina- 
ogra- 
rely 
y ap- 
rpho- 
both 
to- 
only 
his 
18 
pt a 
ssing. 
of 
gra- 
the 
ich 
the 
re- 
me a 
hic 
Ey) EEE 
Subsystem of Information 
roceSSing 
  
  
  
  
  
  
Source |—Encoder Chan >|Decoden-—IReceiver 
p 
  
  
  
  
  
  
  
  
  
  
Noise 
  
  
Fig.5 The general communication 
system 
information system and improve the data base with 
updating. 
Information channel is a physical medium that under- 
takes message transmission in a communication system 
. However, computers that play a channel part in 
digital mapping are not only sending the image in- 
formation but also executing the various mathematic 
and logical operations on the digital imagery such 
as editing, computation of orientation pa ra 
as editing, computation of orientation parameters, 
data interpolation, creation of digital terrain mo- 
dels, feature classification and so forth, 
The encoding procers ina communication system ia 
not performed at once in most circumstances. The 
general mission of encoding lies in that of con- 
verting the messages out of the information source 
into the signals suitable for transmission and pro- 
cessing in the channels, The total enceding is uru- 
ally divided into two parts, that is the source's 
and the channel's, The main objective of the former 
is to improve the efficiency of transmitting mes- 
sage and reduce the the redundancy, and the latter 
Pays attention to enhance of the ability of coded 
rignals to rerist disturbances which is important 
for the distant transmission in particular. Image 
digitization itself is a general encoding of the 
analog-to-digital conversion which aims at trans- 
forming the photo imagery into the discrete pulse 
£ignals which are capable of acceptance and treat- 
ment by computers, The digitized airphoto imagery, 
however, does not serve the Purpose of telecommu- 
nication as TV broadcast, Neverthelere some comru- 
ters need reformatting the initial digital image 
before the routine manipulation. 
Decoder fulfils the inverse tack of encoding pro- 
cess, This kind of operations in digital mapping 
is mostly implemented through plotters and othor- 
photoscopes. These instruments are able directly 
to accept the computer outrut by means of the on- 
line mode, It is also possible of that the content 
of data base created by computer on an external 
storage is postponed to some time and inputted into 
the drawing systems through a reading device under 
the convenient conditions. 
The disturbing source in the hlock diarram repre- 
Frente A met Of various noires impored on the whole 
communication system, Disturbances may occur from 
435 
the heating noise in the electronic circuits owing 
to the ambient condition change as well as the man- 
made interference, Currently one of the most destru- 
ctive troubles to computer information processing is 
the damage from computer viruses, especially the des 
struction to a great variety of programs on many 
microcomputers in widespread use, These troubles 
ere probably incurred during the improper software 
reproduction, We need to take some special appro- 
aches to defend the useful information against 
crash, 
6. CONCLUSION 
As rhotogrammetry and remote sensing are converging 
to a direction of the geographic information mani- 
pulation respectively, many advanced means of image 
Processing from remotely sensed data are gradually 
accepted by photogrammetriste. This trend has pro- 
moted the development of automatic plotting systems 
with a fully digital photogrammetry and the re- 
. search on their application. Moreover most methods 
of digital image processing have benefited from the 
guidance of Information theory fundaments. Today 
the analytic tools and softwares devised by means 
of Information theory are increasingly applied in 
a8 variety of geographic information systems, At 
Prerent the high eracial resolution of airphotos 
is still superior to that of satellite images, thus 
lots of taske such as the large scale mapping, a 
thorough inventory of land use in the county level, 
the civil engineering survey, the regional cadas- 
tral investigation and so ON will be undertaken by 
photogrammetry for a long time to come. The general 
development tendency of image Processing rupgests a 
demand of more sophisticated techniques, It 1s ob- 
vicus that designing the new equipments and methods 
of rhotogranmetry to meet the requirements frcm 
users remains to derend on further understanding 
the essence of digital imagery information, The 
latent power of Information theory and other new- 
ly developing disciplines to the future progress 
of rhotogrammetry is worthy to be deeply tapped 
by us. 
R EF ER ENC ES 
1. Wang Zhizhuo, Fundamentals of Ihotorrammetry: 
A continuation, The prera of purveving and map- 
Ping, China, 19Rfr, 
2, Fi Zuyun, Fundamentals of Informa! fon Theory, 
the press of electronic industry, China, 1680, 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996