3x3 Rules for Simple Photogrammetric Documentation of Architecture

The following text is taken from a paper, which was presented by Peter Waldhäusl, University of Technology, Vienna, Austria and Cliff Ogleby, Department of Geomatics, University of Melbourne, Australia, at the Symposium of the ISPRS Commission V "Close Range Techniques and Machine Vision" in Melbourne, Australia, 1-4 March 1994:

"Simple rules which are to be observed for photography with non-metric cameras have been written, tested and published already on the occasion of the CIPA-Symposium in Sofia in 1988. It was a first edition of such rules, and possibly some amendments are necessary...
... I called these rules for my students the "3x3-Rules", because they are structured in three items, with three sub-items each. There are

3 geometric

3 photographic, and

3 organizational

matters treated. In detail, the rules read as follows:

1 - The 3 geometrical rules

1.1 - Prepare control information: (Fig. 1)

Some long distance between well defined points, eventually targets.
Some plumb-lines,
- Defined ("This is a plumb-line"), or
- Made by plumbing down e.g. a roof corner and by targeting of the foot.
- Do that on several sides of the building for control.

Figure 1:
Minimum metric information

- one distance

- one plumb-line

1.2 - Multiple photographic all-around coverage: (Fig. 2)

Take a "ring" of pictures all around the object, overlapping each other more than 50%.
Take shots from half the object´s height, if possible.
Include parts of the neighbourhood.
Add diagonal shots combining two sides of the object.
Add traversing shots combining the neighbouring photographs.
Include also the roof, if of interest.
Check multiple coverage carefully.
Add orthogonal full facade shots for overview and rectification.

1.3 - Take stereopartners for stereo-restitution: (Fig. 2)

Stereopartners are taken as
- normal case (base-distance-ratio 1:4 to 1: 15), or
- convergent case (base-distance-ratio 1:10 to 1: 15).
Avoid divergent case.
Add close-up stereopairs for valuable details and measure additional control distances for them or add a rod to the object.
Check stereo-coverage carefully.
In case of doubt, add more shots and measures "by hand" whatever remains invisible.

Figure 2:
Ground plan of a stable bundle block arrangement all around a building

2 - The 3 photographic rules

2.1 - The inner geometry of the camera has to be kept constant:

No zooming! Use end position, or avoid zoom optics at all, or fix focus of optics by adhesive tape.
No shift optics.
No distance changes. Fix to indefinite, or mean distance by adhesive tape, but use only
- one distance for "ring"-photography
- one distance for close-ups.
Image format frame of camera must be sharply visible on the images with good contrast.
Don´t cut into format when cutting the original film (=document!).
The true documents are the original negatives. Treat and keep them carefully.

2.2 - Select homogenous illumination:

Plan the best time of day.
Use tripod and cable release for sharp images.
Any film may be used. Black-and-white is sufficient, colour provides advantages for interpretation and documents also the colours. From slides it is more costly to make enlargements.

2.3 - Select most stable and largest format camera available:

Wide angle is better than narrow angle for all-around photography.
Medium format is better than small format.
Calibrated (or metric) cameras are better than non-metric.
Film sucked flat, or kept flat behind a resau glass plate, is better than film with varying bending as in normal cameras.

3 - The 3 organizational rules

3.1 - Make proper sketches:

Ground plan and
Elevation of each side (1:100 - 1: 500).
Note object, owner, address.
Mark north direction and
Photo standpoints (with film and negative number) and photo directions.
Mark single photo coverages and stereo coverages.
Show control distances and plumb-lines.

3.2 - Write proper protocols:

Object, owner, address.
Date.
Camera, optics, focus and distance settings.
Calibration report, if available.
Description of place, object, history.
Bibliography.
Specials, artists, architects, permissions, obligations, etc.

3.3 - Don´t forget the final check:

Write down everything immediately.
Check completeness and correctness before leaving the site.
Conclude the reports while you remember all details.
Check the results at home together with an authority for monuments and sites.
Plan next project bearing in mind any mistake made previously. Learn."

Reference:

WALDHÄUSL, P., OGLEBY, C.: 3-by-3- Rules for Simple Photogrammetric Documentation of Architecture. In: J.G.Fryer (Editor): Close Range Techniques and Machine Vision. Proceedings of the Symposium of Commission V of ISPRS in Melbourne, Australia, 1-4 March 1994. IAPRS XXX/5, 1994, 426.