The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008 
5. CONCLUSIONS 
We have metrically calibrated and we have tested the metric 
accuracy of four consumer-grade imaging devices: Two mobile 
phone cameras (Sony Ericsson K750i and Nokia N93) and two 
still video cameras (Sony DSC W100 and Sony DSC F828). 
The tests were performed by using our in-house 3D testfield. 
We have found unwanted effects from image enhancement 
(sharpening) in the K750i, N93 and W100 cameras and JPEG 
compression artifacts in the N93. In all four cases we have used 
(more or less) the same imaging geometry, and imaging 
conditions in order to make the results comparable. With the 
given strong geometrical set-up of course all parameters for the 
interior orientation could be calibrated reliably. The accuracy 
tests showed that in all cases the theoretical expectations, as 
defined by the average standard deviations of the object space 
coordinates, could not be achieved by the empirical RMSEs, 
computed from checkpoints. The deviations range from factor 
3.3 (K750i) to factor 1.7 (F828). While the sigmaO values of the 
K750i, N93 and W100 are all at a 1/5 pixel level, they drop 
down to 1/10 pixel with the F828. This improvement in sigmaO 
is matched by the better behaviour of the post-adjustment image 
residuals. Only in case of the F828 do we get an almost random 
distribution. The other cameras, in particular the K750i, suffer 
from strong image-variant systematic errors. Since we have 
used in our self-calibration only block-invariant additional 
parameters these errors could not be compensated. The error 
patterns are also not in agreement with what we are used to in 
photogrammetry. Therefore, our standard additional parameter 
functions cannot compensate these defects. So far we cannot 
explain the reasons for these errors. Could they lie in the image 
enhancement procedure or any other shortcomings in the 
electronic circuits? Nevertheless, and despite these problems, 
we could reach relative accuracies of 1:8 000 in-plane and 
0.03% of average depth with the K750i and 1:34 000 in-plane 
and 0.005% of average depth with the F828, using in both cases 
10 control points. This superior behaviour of the F828 can only 
partly be explained by the larger image format (8 Mpixels 
versus 2 Mpixels), which theoretically should only lead to an 
improvement of factor 2. 
If we apply to both cameras a free network adjustment by 
minimizing the trace of the covariance matrix for the object 
space coordinates we get the following values: 1:25 000 and 
0.009% for the K750i and 1:99 000 and 0.0025% for the F828. 
This shows roughly the same relationship between both 
cameras, it gives however a better indication of the potential 
system accuracy. It is worthwhile to note that, compared to the 
film-based large format aerial photogrammetric block 
adjustment accuracy, we can achieve here the same and better 
accuracies in height and almost the same in planimetry, if we 
consider for the aerial case an object area of one image 
coverage only (like in our close-range case). This definitely 
indicates the great potential of consumer-grade and even mobile 
phone cameras for photogrammetric processing. The main 
remaining problem is to find a convincing explanation for the 
image-to-image varying systematic error pattern in some of the 
mobile phone cameras. 
In a final test we also checked the effect of JPEG compression 
on the metric system accuracy for the F828 camera. Even when 
going up to a factor of 42 compression rate we did get only a 
small reduction in accuracy (9% in depth direction). This can be 
considered harmless. We spread the tests of the N93 over a 
longer time period in order to check the temporal stability of the 
calibration. We observed that the interior orientation of N93 did 
not change significantly according to our one dimensional 
statistical test procedure. We plan to repeat the significance test 
with a multi-dimensional test. 
Our future plan is also to invest some more work into image 
quality studies. We believe that with a proper calibration and 
data processing software performance these devices can be used 
for many photogrammetric tasks which require an accuracy of 
around 1:10 000. The integration of GPS receivers and motion 
sensors will further broaden their applicability. Also, it is to be 
expected that the quality and performance of the integrated 
cameras will further improve, together with the on-board 
processing functions. This may allow one day such a device to 
be used as a stand-alone photogrammetric data acquisition and 
processing tool, at least for smaller projects. In conclusion we 
can state that mobile cameras do give us a very interesting 
option for doing “mobile photogrammetry”, in terms of 
accuracy, costs and flexibility. 
ACKNOWLEDGEMENTS 
The authors thank Mr. Thomas Hanusch and Dr. Timo 
Kahlmann for helping with the geodetic measurements of the 
testfield and Dr. Jafar Amiri Parian for running his self 
calibrating bundle adjustment software with 44 additional 
parameters. 
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