646 
Rottensteiner, Grussenmeyer, Geneva 
Additional information called “constraints” can be defined. There are three main categories of constraints in PhotoModeler: multi 
photo constraints, axes constraints, and control point constraints. In version 4, new functions are available: constrain the distance 
between two points to a given value, constrain points to fit on a plane, constrain two lines to be perpendicular or to intersect at a 
given angle, constrain lines or edges to have the same length or to be parallel, constrain two edges to intersect or constrain an edge to 
intersect a point. These constraints can be compared to GESTALTs in ORPHEUS, which, however, offers more possibilities for 
defining fictitious observations. 
The steps of the work flow for the generation of 3D photo models described in section 2.2 are the same for both software packages. 
The progress and reliability of the restitution is visualised by a 3D-viewing tool using the Windows Direct3D interface. Orthophotos 
of complex surfaces can be produced and exported as bitmaps. The export formats for the spatial result are wide-spread and include 
DXF, 3D-Studio, VRML and some others. 
4.3 Remarks about photogrammetric adjustment 
The user interface of the adjustment module is prepared for being used by non specialists. Only a few parameters can be defined by 
the user. Termination parameters for optimisation (such as maximum iteration, solution tolerance), default point standard deviation 
weights in pixels and self calibration or field calibration parameters can by changed in the preferences interface. The processing of 
the block of photographs follows three steps : exterior orientation, global optimisation and self calibration (optional). No details are 
given about the algorithms in use, but several accuracy studies have confirmed the robustness of the bundle software (EOS, 2001). 
Problems may occur when the adjustment process fails, and the lack of robust estimation and data snooping to eliminate gross errors 
(as available in ORPHEUS) makes the processing difficult when several control points are doubtful. The complementary use of 
ORIENT’S adjustment module was very helpful in our example. 
In Photomodeler, the factors of quality given by the software for each point are: precision in (X, Y, Z), numbers of photos, tightness 
(a value used to indicate the accuracy of an object point's photo markings), angle (between the photographs that image an object 
point), constraints. The user has to analyse this factors in order to obtain a reasonably good solution, and if necessary to try different 
solutions. 
The project computed with Photomodeler was based on 29 photographs from both cameras. The false planimetric coordinates of 
point 311 have been confirmed. The final solution has been processed by fixing points 101-113 only, as proposed in paragraph 3.1.2 
and the same conclusions have been verified. 
5. CONCLUSION 
It has been shown that both blocks of the Zurich city hall data set could be handled successfully using ORPHEUS/ORIENT. The 
tools for error analysis provided by this software package turned out to be well-suited for applications in architectural 
photogrammetry, and they were capable of detecting “hidden” errors in the original data set which had not been detected yet: The 
control point co-ordinates of the data set were detected to contain gross errors, and it was found out that the Olympus images were 
taken with two different focal lengths. These results were confirmed by the photogrammetric package PhotoModeler. With respect to 
the creation of 3D photo models, ORPHEUS could be used without problems, and the principle of using GESTALTs for the 
determination of points on single rays was applied successfully. Future work will concentrate on improving the work flow of 
geometric modelling in ORPHEUS: currently, a certain overhead in the work flow is caused by ORPHEUS being restricted to 
triangular faces. This restriction will be eliminated by a new module for editing polygons in the next release. Of course, the 
questionnaire provided by the authors of the Zurich city hall data set was filled in with respect to ORPHEUS. Persons who are 
interested in it are encouraged to contact the authors by e-mail. 
REFERENCES 
Carey R., Bell G., 1997: The Annotated VRML 2.0 Reference Manual, Addison-Wesley Developers Press, ISBN 0- 201-41974-2. 
Dorffner L., Forkert G., 1998: Generation and visualization of 3D photo-models using hybrid block adjustment. Photogrammetry & 
Remote Sensing 53:369 - 378. 
EOS, 2001. PhotoModeler Product Information (http://www.photomodeler.com) 
Kager, H., 1989: ORIENT: A Universal Photogrammetric Adjustment System. In: Griin, A. & Kahmen, H. (Eds.): Optical 3-D 
Measurement. Herbert Wichmann Verlag, Karlsruhe: 447-455. 
Kager, H., 2000: Adjustment of Algebraic Surfaces by Least Squared Distances. International Archives of Photogrammetry and 
Remote Sensing 33 (B3): 472-479. 
Streilein, A., Grussenmeyer, P., Hanke, K., 1999: Zurich city hall - A reference data set for digital close range photogrammetry. 
Proceedings of the XVII th CIPA Symposium in Olinda/Brazil. 
Streilein, A., Hanke., K., Grussenmeyer, P., 2000: First experiences with the "Zurich city hall" dataset for architectural 
photogrammetry. International Archives of Photogrammetry and Remote Sensing 33 (B5), pp. 772-779.