(units m) 
  
  
  
  
  
  
  
  
  
  
map scale 
1:10,000|1:5,000 |1:2,500 |1:1,000 |1:500 
photo scale 
1:50,000 1.58 0.90 0.63 0.52 0.51 
1:30,000 1.53 0.81 0.48 0.34 0.31 
1:10,000 1.50 0.76 0.39 0.18 0.13 
1: 5,000 1.50 0.75 0.38 0.16 0.09 
1: 2,500 1.50 0.75 0.38 0.15 0.08 
1:50,000 1.52 0.79 0.45 0.29 0.26 
1:30,000 1.51 0.76 0.40 0.21 0.17 
1:10,000 1.50 0.75 0.38 0.16 0.09 
1: 5,000 1.50 0.75 0.38 0.15 0.08 
1: 2,500 1.50 0.75 0.38 0.15 0.08 
Table 2: Graphical plot of photogrammetric point 
data( Precision AT ; High Precision AT ) 
3.1.2 Photogrammetric digital data collection 
Photogrammetric digital data collection is 
equivalent to digital mapping, whereby the 
resulting digital data is either stored in one or 
several data bases for further processing vithin a 
GIS or is used to produce or up-date graphical 
maps. 
Phase I: data collection 
This initial phase of data collection covers the 
whole mapping process. The input errors include 
the errors in ground control and aerial 
photography (as outlined in 3.1.1), in addition to 
the aerial triangulation errors: point transfer 
errors; system errors depending upon the number 
and distribution of tie points and measuring 
errors which vary with the type of point 
(signalised or pricked) and further depend on 
image quality, object quality, the measuring 
instrument, the base-height ratio and observer 
acuity. 
The measuring errors include errors 
relative and absolute orientations; measuring 
errors, which vary depending on whether the 
measuring mode is static or dynamic and, in the 
latter case, the measuring speed; the image 
quality; the base-height ratio; the object 
quality, including parameters such as terrain 
slope, vegetation coverage, etc.; the instrument 
errors; the operator acuity; etc. A separate 
component of the measuring error is the 
identification error, which varies with the 
definition of the feature being measured i.e. 
corner of a house or boundary of a forest. 
Identification errors also arise if the definition 
of the feature to be picked up is not clear enough 
e.g. if it is not clear whether the boundary of a 
canal is to be taken as the top of the bank or the 
water line, etc. 
in the 
The accuracy standards for the digital mapping 
phase are not difficult but are time-consuming to 
establish and verify. 
Looking to the components involved, 
- the A.T. accuracy is obtained from the A.T. 
results 
- the measuring accuracy is obtainable from 
repeated model measurements, such as occur in 
checking operations. The coordinate differences 
used should only refer to well-defined points 
i.e. those without an identification error 
596 
- the identification accuracy for different 
features and different feature definitions is 
obtainable from repeated model measurements at 
these features. 
It is, of course, à tremendous task to build up 
this data base for the identification accuracy of 
different features, particularly since this 
accuracy varies with feature definition (i.e. 
centre of road or edge of road) and with the photo 
scale used. This task will unquestionably become 
part of the checking operations. 
In order to have figures for discussion and 
comparison purposes, the following realistic 
assumptions are made, using figures obtained in 
practice: 
- A.T. accuracy: o - 10 um at photo scale, for a 
precise A.T., which is 
sufficiently accurate for all 
mapping purposes 
- measuring accuracy: o - 15 um at photo scale 
- identification accuracy: control point 0 cm 
wall 5 cm 
hedge, ditch 10 cm 
canal bank 20 cm 
river bank 50 cm 
From these figures, the folloving table can be 
drawn up for the accuracy 
digital data collection. 
of photogrammetric 
  
  
  
  
  
  
  
(units m) 
Identif. 
error|0 cm 5 cm 10 cm |20 cm |50 cm 
Photo scale 
1:50,000 1.00 | 1:00 ] 1.00 | 1.02 | 1.12 
1:30,000 0.60 0.60 0.61 0.63 0.78 
1:10,000 0.20 0.21 0.22 0.28 0.54 
1: 5,000 0.10 0.11 0.14 0.22 0.51 
1: 2,500 0.05 0.07 0.11 0.21 0.50 
  
  
  
Table 3: Photogrammetric digital data collection 
Note: The first column in the above table gives 
the intrinsic accuracy of the digital data 
base i.e. the accuracy excluding a possible 
identification error. 
Phase II: data storage and processing 
Since no further processing takes place until the 
data are eventually incorporated into a GIS, the 
accuracy of the photogrammetric data after initial 
storage and processing will be the same as that 
shown in figure 3, after data collection. 
Phase III: data presentation 
  
A graphical plot is a quite normal requirement to 
be produced from photogrammetric digital data. 
With a standard plotting accuracy of 0.15 um at 
map scale, tables can be drawn up showing the 
accuracy of the graphical plot of photogrammetric 
digital data collection. Note, however, that 
different tables are needed for the different 
values of the identification error. The table 
given below refers to intrinsic data i.e. with no 
identification error.