The ratio ox max/ox mean is very close to ey max/oy mean all the time. In the case of a dense peri- 
meter control this ratio is in the order of 1.2 for blocks with few strips and in the order of 1.1 for 
he larger blocks. With the other control variants omax/omean increases up to a factor 2.0. These 
values are true for 20 9, sidelap as well as for 60 95. 
In order to determine the height accuracy for each block the standard deviations of the z coordinates 
of approximately 100 or more representative minor control points were computed. 
For 20 95 sidelap 2 types of height control were investigated 
H1: dense perimeter control only, distance 2 base lengths 
H2: some lines of control as shown in figure 3 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
i/2 models i/2 models 
kbridgedzl kbridged = 
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D D- 
o ®- O 
ki models bridged =| | models bridged = 
  
  
H2 H3 
Fig. 3: Height control distributions H2 and H3 for 20% sidelap 
The control variant H1 yields a remarkable simple accuracy law. Both, the mean square standard 
deviation oz mean and the maximum standard deviation oz max are in extremely good approxima- 
tion a linear function of the number ns of strips in block. 
Hl: ez mean — 4.1 um ns (8a) 
oz mean/oz ~ 0.41 ng (8b) 
oz max ~ 5.7 um ns (9a) 
cz max/oz — 0.56 ns (9b) 
In (8b) and (9b) oz mean and oz max are expressed in units of the standard deviation oz of the 
height coordinates of the model points (table 1). 
With. control variant H2 the standard deviations oz mean and oz max can be approximated very 
well by a linear function of the number of models i, bridged by lines of control. 
H2: oz mean — 3.5 um 4- 2.2 um i (10a) 
dz meanjoz c 0.34 + 0.22 i (10b) 
oz max — 2.8 um 4- 3.2 um i (11a) 
oz max/oz ~ 0.27 + 0.31 i (11b) 
The formulas (10) and (11) are practicly independent of the size of blocks. 
An attempt to save each second point along the lines of height control inside the block (variant H3 
in figure 3) resulted in standard deviations increasing to 4 oz at points positioned between the control 
points along a line. So control distribution H3 cannot be recommended. 
For 60 95 sidelap only one type of height control was investigated. 
H4: height control points in a quadratic screen as shown in figure 4.