Faculty of Architecture and Civil Engineering
Laboratory for Visual and Virtual Reality
Prof. Dr.-Ing. Guenter Pomaska

A project based study of documentation of watermill in Kalletal was carried out under scope of the lectures Applied Photogrammetry in Architectural Restoration. The building watermill was selected in collaboration with Westfaelisches Amt Denkmalpflege. Including facade drawings and 3D models, documentation was accomplished by a master student, Funda Yaka, from Izmir Institute of Technology, Department of Architectural Restoration during her studies at Bielefeld University of Applied Sciences as an Erasmus student. These studies focused preliminary on the façade survey applying close-range photogrammetry.

Kalletal-Langenholzhausen is located in Germany, North Rhine-Westphalia between the cities of Bielefeld and Detmold, an area where wind- and watermills are wide spreaded. The distance from Minden, where the Faculty of Architecture and Civil Engineering is located, takes 27 km. With permisssion of the LVA NRW we can display here a part of the DGK 5 and an aerial image. Click the links to popup a map.

The building dated 1528, is one of the historical mills, still in function until a few years ago. The building stands from South to North direction and water wheel is placed on the West, driven by the water of the beck Kalle. Today, although it remains with the dimensions 10.40m wide and 17.70m long, traces coming from the building lead to the idea, that the building was extended through North in an earlier period. Moreover, a silo was constructed from sand-lime brick in 20th century. The original building was built with rubble stone masonry and timbered gable. The framework is left exposed which allows detecting of construction traces like treenails, beam marks and alterations, for a research in the building's history.

Photography

Photos were taken with a Nikon D1X, focal length 18 mm. Image resolution is 3008 px x 1560 px with a sensor size of 23.462 mm x 15.6 mm. Camera calibration was provided by AICON, Braunschweig. click into the icons for image enlargement.

Click here for a graphical view of the lens distortion values generated within Rolleimetric CDW software.

Total Station Measurements

A survey network with a local datum definition estabishes a basis for all further measurements. Common is a layout as a closed traverse. If required, more traverses can be adjusted to the basic co-ordinate definition. The network provides survey positions and control points for appropriate free positioning of a total station. Control points for photogrammetric orientations and points of interest are calculated by spatial intersection or measured directly with reflectorless distance measurement. Photogrammetric control points have to be marked in images for identification with a unique point number. After computation a list of point co-ordinates should be available, as well as a graphic conversion to DXF.

Multi Image Photogrammetry

Multi image photogrammetry enables exact determination of geometric values from photos. Image co-ordinate measurements are used to calculate object information by complex software packages. From those measurements 3D-CAD models can be constructed. A building has to be photographed from arbitrary directions, so that the complete information is covered on several photos. Additional measurements to determine the photo positions are not required on site. The exposure directions should be convergent to each other. Photo positions must differ. A distance on the building has to be measured for scale defintion.

At the outlet image measurements of corresponding points have to be carried out. The calculation of the photo position follows. In practice more points then necessary are taken, therfore the system is over determined. A best fit of all observations applying a bundle adjustment procedure is recommended. Afterwards all details can be measured and stored as raw data.

Photo Orientation

A photogrammetric process delivers exact photo position and co-ordinates of so called orientation points. Included are basic statistics about the adjustment calculation. The project presented here is separated into three small image bundles. Data structure follows the DTD recommendation given by Pomaska/Dementiev in PFG IV, 2005. Follow the links to review the photogrammetric process applying an XSL transformation to the XML File.
Click here: [ NORTH | WEST | SOUTH ]

Exposure arrangement and the object in general is available as a SVG format. Camera icons include a link to the metric image, taken from that position. SVG viewer installed?
Click here to view the plan view of the project.

Elevation Drawings

The elavation drawings have been constructed within AutoCAD, based on the raw data provided by the photogrammetric evaluation. Conversion from DXF into the SVG format has been carried out with a software developed at the VR-Lab. Drawing layout is driven by style sheets. SVG viewer is required to navigate through the drawings. Click into the icons to load the SVG files in a blank target window.

Single Image Rectification

If plane surfaces can be estimated, correction of camera tilt (and direction) can be performed due to the projective relationship between object and image. A polygon of minimum four control points must be known in the object. Comparison between object co-ordinates and measured photo co-ordinates provides the transformation matrix with its eight unknowns. Are there more as four points known, the system can be calculated by over determination. In the latter case accuracy information is provided too.Instead of control points parallel lines in two directions can be used to constrain the exact geomtry. wo distances in the object are necessary for getting the dimensions. But a digital single image rectification is still a perspective. In architectural applications one can detect this by observing window or door openings. Applying digital image procedures is helpful for improving results by geometric and if required radiometric corrections.

Click in the images will popup an enlarged window. An overlay of the rectified facade raster image with the vector data will be displayed as a SVG format if you click in the facade icon on the left

Solid Modeling

Photogrammetric raw data and the detailed facade evaluation provide the geometric data for the construction of a 3D model. A solid model is constructed by utilising boolean operations to geometric primitives. Next to the geometric definition material can be defined for the appearance of geometric elements. Here colors are used together with surface propertiies. Shadows are displayed by a sunlight simulation. The three epochs of the watermill are calculated from the same perspective and can be viewed in an animation. Click into one of the images below to start the animation.

3D Images

3D images are separately calculated for a left eye and a right eye position. The anaglyph process filters image information applying red/cyan filters. This leds to a colored 3D image while wearing the appropriate glasses. Click into the icon on the left to load a 3d image.

Virtual Reality Modeling

Virtual Reality is a reality near description of 3D worlds under consideration of interactive visiting by the user. Amongst visual descriptions like geometry, material a.o. physical properties belong to a definition of a virtual world.

For the formulation of virtual worlds the description language VRML (Virtual Reality Modeling Language) can be used. A newer version of VRML is X3D, that language implementation follows the XML standard. Export utilities from CAD to VRML or X3D are available inside CAD systems. Elements of the language include geometry, appearance, light sources, environment descriptions, animations, interactivity and sound. Publication of VR worlds on the Web is realized by providing VRML files (file extension wrl). The Multipurpose Internet Mail Extension (mime type) is "model/world". Interactive navigation through VRML-files from the Internet or local harddrive requires a VRML browser. Plug-ins are available from different sources. The icon on the left guides you to ParallelGraphics for downloading a VRML client.

Click here for loading the VRML/X3D model of the watermill Kalletal into your VRML client.
The root file is mill.wrl and uses INLINE nodes. Click here to download the complete ZIP file.

Pomaska, Guenter; Dementiev Nikolai
XML basierte Datenformulierung zur Web-konformen Dokumentation photogrammetrischer Bauaufnahmen. Zeitschrift fuer Photogammetrie, Fernerkundung, Geoinformation, 4/2005, S.291-301

Pomaska, Guenter
Grundkurs Web-Programmierung.Vieweg-Verlag, Wiesbaden 2005

Pomaska, Guenter
Introduction of SVG as a data interchange format for architectural documentations. CIPA International Symposium, Antalya, Turkey, 2003

Responsible for the content of this site is Prof. Dr.-Ing. Guenter Pomaska, Laboratory for Visual and Virtual Reality, Faculty of Architecture and Civil Engineering, Bielefeld University of Applied Sciences

It is not allowed to use the published measurement results for any further processing. There is no guarantee given for the correctness of the data, drawings and images presented here.

Contact and requieries: Please mail to gp@imagefact.de