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Figure 3 : Orthographic projection of the west facades of the castle 
The analytical vector structure provides the 
geometrical frame for the digital model which may give 
pixel information for every point on an object's surface. 
Figure 2 shows the facade drawings generated with 
the RolleiMetric MR2 program. Included are the photo 
position which are calculated by the photogrammetric 
orientation procedure. Reconstruction of the roof is 
shown in this stage as well. 
DIGITAL IMAGE RECTIFICATION 
Warping digital images is a process that defines a 
geometric relationship between each point in an input 
and output image. The mapping function for 
rectification is a perspective transformation based on 
the relationship between the image and the planar 
object. With a minimum set of four control points given 
in the image and on the object surface the eight 
degrees of freedom for a perspective transformation 
can be determined. Forward mapping consist of 
copying each input pixel onto the output image to 
positions determined by the mapping function. Inverse 
mapping projects each output coordinate into the input 
image. The value of the data sample at this point is 
copied onto the output pixel. Inverse mapping 
guarantees that all output pixels are computed. The 
output image in this way is generated by point 
sampling. With point sampling, entire intervalls 
489 
between samples are discarded. Interpolation is 
required. When large scale changes occur, aliasing 
articfacts such as jagged edges or moire patterns are 
evident.  Antialiasing algorithms have to be 
implemented. Fast warping techniques are critical for 
the application. Scan line algorithms have reduced 
complexity and processing time. 
The RolleiMetric MSR software rectifies images with 
respect to the a.m. theory taking into consideration 
interior orientation parameters of metric cameras. The 
control points are imported from the multi image 
evaluation results and represent a 3D-surface. 
Maximum distance from the average plane is shown. 
Due to the overdetermined calculation of the 
transformation parameters quality control of the 
rectification is given by the residuals. The output image 
represents a surface on the object with a predefined 
pixel distance. The offset of the pixel coordinate 
system is stored in user coordinates in a separate file. 
This information yields to user coordinates for every 
pixel and is useful for further processing such as 
scaling , clipping or merging image data. 
Acquisition of Digital Images. Digital image 
acquisition is provided by use of a digital camera, slide 
scanning or desktop scanning. Resolutions of digital 
cameras are often insufficient. Handling of high 
resolution equipment is not convenient on site. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B5. Vienna 1996