-38- 
A bit surprisingly, it can be noticed that the Optech system has 
relatively big differences relative to the “true distances” and 
varies in a strange way over the measured distance. Since the 
measurements was done between the modelled planes better 
results was expected. Possibly this has something to do with the 
system not being perfectly calibrated. 
Looking at the Cyrax system it gives very good results, results 
within the range for the possible accuracy achieved with the 
Trimble total station. 
3.2 How well can the reality be represented? 
Evaluation has just started and from what have been noticed all 
three systems have problems along edges of objects. Looking at 
the ILRIS-3D data, these edge effects are relatively big, also 
causing problems in resolving objects. It can sometimes be 
difficult to see what belongs to what object. 
As expected the big spot size of the LMS-Z210 also makes it 
difficult to resolve small objects from each other. 
Cyrax, on the other hand is relative to the other two tested 
systems extremely good in resolving small details. The small 
spot size penetrates small openings and registers differences in 
depth very well. 
3.3 Different reflectivity and its influence on measurements 
From the test it was clear that the Cyrax system was not capable 
of measure distances to material with low reflectivity after the 
recommended range of 50 meter was exceeded. This is probably 
what could be expected, but we have also noticed at other 
occasions that our system sometimes looses points within the 50 
meter range, especially on objects that seams to have low 
reflectivity. 
At one occasion scanning outside at night-time the system 
clearly lost points in the very dark areas, but on same material, 
in lit up parts of the object area, points were registered. This 
problem is still being investigated and as mentioned in the 
background and theory part of the paper we are not sure 
whether the system needs to be re-calibrated. 
4. SUMMARY 
High-resolution ground based laser scanning systems will 
probably play an important role in future documentation of 
buildings. However, it is important to understand where 
possible erroneous points can be found to be able to evaluate 
and make use of the resulting point-clouds in a comfortable 
way. 
It has been noticed that all three tested systems gives similar 
unwanted effects in the resulting point clouds. Two of them are; 
Strange effects along edges of objects and problems with 
recording points on certain materials. This is important to have 
in mind when planning a laser-scanning project. Will the 
chosen laser-scanning system resolve the details I want to 
document and what influence will the objects material have on 
the results? 
A small spot size and a system with good range and point 
position accuracy resolve details best. Not only will this give 
the most accurate model of the documented object but having a 
point cloud that has resolved fine details good makes modelling 
much easier. It is easier to actually see which part of the point 
cloud should belong to which modelled object. 
The work on evaluating high-resolution ground based laser- 
scanner data at Gävle GIS Institute will continue and our goal is 
to contribute with results from further evaluations in near 
future. 
5. ACKNOWLEDGMENTS 
First of all I would like to thank Mr. Ake Lindberg, research 
assistance at Gävle GIS Institute for all his help, his way of 
inspiring me, and contributing with good ideas from his 
extensive knowledge in surveying of buildings. 
I would also like to thank Dr. Ulf Söderman and Mr. Hakan 
Larsson, both at the Swedish Defence Research Institute in 
Linköping, for all their help with the tests. 
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