The following text is adapted from a paper presented by Peter Waldhäusl (University of Technology, Vienna, Austria) and Cliff Ogleby (Dept. of Geomatics, University of Melbourne, Australia), at the ISPRS Commission V Symposium “Close Range Techniques and Machine Vision” in Melbourne, Australia, 1994. Simple rules that are to be observed for photography with non-metric cameras have been written, tested and published at the CIPA Symposium in Sofia in 1988.
1 – THE 3 GEOMETRIC RULES
1.1- CONTROL
• Measure some long distances between well-defined points.
• Define a minimum of one vertical distance (either using plumb line or vertical features on the building) and one horizontal.
• Do this on all sides of the building for control.
• Ideally, establish a network of 3D co-ordinated targets or points.
1.2- WIDE AREA STEREO PHOTOCOVER
• Take a ‘ring’ of pictures around the subject with an overlap of greater than 50%.
• Take shots from a height about half way up the subject, if possible.
• Include the context or setting: ground line, skyline etc.
• At each corner of the subject take a photo covering the two adjacent sides.
• Include the roof, if possible.
• No image should lack overlap.
• Add orthogonal, full façade shots for an overview and rectification.
1.3- DETAIL STEREO PHOTOCOVER
Stereo-pairs should be taken:
• Normal case (base-distance-ratio 1:4 to 1: 15), and/or
• Convergent case (base-distance-ratio 1:10 to 1: 15).
• Avoid the divergent case.
• Add close-up square on stereo-pairs for detail and measure control distances for them or place a scale bar in the view. Check photography overlaps at least 60%.
• If in doubt, add more shots and measured distances for any potentially obscured areas.
• Make sure enough control (at least 4 points) is visible in the stereo image area and at least 9 control piubnts in the single image area.
2 – THE 3 CAMERA RULES
2.1 – CAMERA PROPERTIES
• Fixed optics if possible. No zooming! Fully zoom-out, or fix the focus using adhesive tape or avoid zoom optics altogether. Do not use shift optics. Disable auto-focus
• Fixed focus distance. Fix at infinity, or a mean distance using adhesive tape, but only use one distance for the ‘ring’-photography and one distance for close-ups.
• The image format frame of the camera must be sharply visible on the images and have good contrast.
• The true documents are the original negatives or digital ‘RAW’ equivalents. Use a camera with a highest quality format setting.
2.2 – CAMERA CALIBRATION
Use the best quality, highest resolution and largest format camera available:
• A wide-angle lens is better than narrow angle for all round photography. Very wide-angle lenses should be avoided.
• Medium format is better than small format.
• Calibrated cameras are better than not calibrated.
• Standard calibration information is needed for each camera/lens combination and each focus setting used.
• A standardised colour chart should be used.
2.3 – IMAGE EXPOSURE
Consistent exposure and coverage is required.
• Work with consistent illumination: beware deep dark shadows!
• Plan for the best time of day
• Use a tripod and cable release/remote control to get sharp images.
• Optimise shutter speed and aperture by using a ‘slow’ ISO setting ..
• Use RAW or ‘high quality’ or ‘fine’/’super fine’ setting on digital cameras.
• Test and check the exposure using the histogram to understand the balance needed.
3 – THE 3 PROCEDURAL RULES
3.1 – RECORD SITE, CONTROL & PHOTO LAYOUT
Make proper witnessing diagrams of:
• The ground plan with the direction of north indicated
• The elevations of each façade (1:100 – 1: 500 scale). Show the location of the measured control points.
• Photo locations and directions (with frame number).
• Single photo coverage and stereo coverage.
• Control point locations, distances and plumb-lines.
3.2 – LOG THE METADATA
Include the following:
• Site name, location and geo-reference, owner’s name and address.
• Date, weather and personnel. Client, commissioning body, artists, architects, permissions, obligations, etc.
• Cameras, optics, focus and distance settings.
• Calibration report, if available.
• Description of place, site, history, bibliography etc.
• Remember to document the process as you go.
3.3 – ARCHIVE
Data must be complete, stable, safe and accessible:
• Check completeness and correctness before leaving the site.
• Save images to a reliable site off the camera.
• Save RAW formats to convert into standard TIFFs. Remember a CD is not forever!
• Write down everything immediately.
• Don’t crop any of the images – use the full format.
• Ensure the original and copies of the control data, site diagrams and images are kept together at separate sites.
Although these rules were devised for ‘classical’ (stereo) phtogrammetic recording they hold true for photocover in general. The rules have been modified to suit digital camera work and have not incorporated the use of the Exif data in processing the images.