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Photogrammetry > Laser Scanning
I’d argue that for preservation work, photogrammetry can often provide a richer sort of architectural documentation than laser scanning techniques. There are merits to both techniques and their products, of course – each has its strengths vis-a-vis the other.
When comparing the products of photogrammetry and laser scanning, I find it interesting to see how they are converging and looking more and more alike as each respective technology continues to advance. Simply put, photogrammetry is producing richer and richer point clouds (a strong point for laser scanning) while laser scanning is producing higher fidelity imagery than ever before (but still far from the photographic quality required for sensitive preservation work).
But in some cases, photogrammetry wins the argument as to which technique is more appropriate to the task because it can perform in conditions that render laser scanning impossible. This is even more true when one factors in what it costs to get a project from start to finish.
An ocean facing portion of Fort Sumter shot with a long lens
Take for example the work completed at Fort Sumter in Charleston Harbor by Aaslestad Preservation Consulting late last year. In order to precisely map the layout, composition and condition of the fort’s exterior masonry walls, Aaslestad shot photos from a pitching boat!
Above is one of the shots used in the survey. It was shot with a 200mm lens from a small craft that the Park Service provided Aaslestad to circumnavigate (as much as possible) the fort. Later that day during the peak of low tide, Aaslestad was able to scramble around the the perimeter of the fort to collect a series of 16mm shots as well, see below.
The same ocean facing portion of Fort Sumter shot with a wide angle lens
So the versatility of using a handheld camera for ‘data capture’ can make some jobs possible through photogrammetry that would otherwise be either impossible or much more time intensive and expensive. To be sure, a laser scanner is a fabulous piece of equipment that can produce incomparable results for some applications – but it needs a stable platform from which to operate (therefore can not be used from a pitching boat!). Repositioning a laser scanner around the perimeter of Fort Sumter (on these slippery rocks shown above) during the relatively small window of opportunity of extreme low tide would also be unfeasible, or at the very least impractical and time consuming/expensive.
Another example of the versatility of using camera equipment for data capture with preservation in mind is the use of a telescopic tripod. The shot below was taken using a remote shutter release while the camera was suspended 25′ above grade on a a tripod. Gaining points of views such as this can sometimes make the difference between be able to document a surface or not – or at the very least of enhancing a survey through greater quality of coverage.
The courtyard at Fort Sumter from atop a telescoping tripod
Looking into the future we may see devices the size of an iPhone hovering around a structure like a miniature drone collecting 3-D scan data and high resolution digital imagery – maybe even sonography or thermography as well – but until then I’m very happy to rely on the versatility provided by a calibrated SLR.
Posted in Uncategorized
Tagged compare, comparison, data capture, laser scanning, Photogrammetry, point cloud, preservation, rectified imagery, survey
Page Updates: Point clouds, F&M, Roxboro
I’ve updated my page on point clouds with some new images from Franklin and Marshall’s Goethean Hall that show some of the true color point clouds generated though photogrammetry. Likewise, I’ve update the page on the Roxboro House project to include some point cloud views.
Posted in Uncategorized
Tagged 3-D, Franklin and Marshall, laser scan, mesh, metrology, nurbs, Photogrammetry, point cloud, polygon, Roxboro
Sharing: Middlebrook Avenue
Two more screenshots to share, this time of a streetscape project on Middlebrook Avenue here in Staunton, VA. The first shows a virtual aerial view of the the automatically created point cloud, the second of the assembly of photos used to create the point cloud. Both are screen shots from Elcovision software.
Middlebrook Avenue point cloud
Middlebrook Avenue Photos
Posted in Uncategorized
Tagged elcovision, Middlebrook Avenue, Photogrammetry, point cloud, Staunton
Sharing: more Claude Ledoux, Quai Vauban & Besancon
Theatre (Besancon) Nicolas Claude Ledoux 1784
Here are some screen shots of the point cloud depicting the theater in Besancon designed by Ledoux in the 18th century.
Point Cloud of Theater
This was created with a few “snap shots” of the building taken from the street.
Photos used to create point cloud
In order to capture roof elements and such additional photos would be necessary. As a “piece” of the street however, it can be assembled along with additional scans to create a larger whole.
A few more screen shots from a separate locations in Bescanson, across form the Prefecture:
Screen capture from Elcovision
And an “aerial view” of a point cloud that encompasses the entire Quai Vauban:
The Quai Vauban
Posted in Uncategorized
Tagged besancon, claude nicolas ledoux, Photogrammetry, point cloud, prefecture, quai vauban, street, theatre
More lost blog posts: Arc de Triomphe
L'Arc de Triomphe
Re-posted here are some of the images collected this past summer of the Arc de Triomphe in Paris. These were made as a sort of demo project following some training sessions in which I was learning how to create rich 3D point clouds from photographs.
Axonometric view of point cloud
Looking at these images now, they don’t seem terribly “rich” as 3D point clouds – I’ve since learned how to do this work better – but they are a good start. For one thing, they were the successful resolution of an automatic analysis module ( a big time saver).
"RCP" of point cloud
Individual photos with point measurements shown
Screen shot from Elcovision
Posted in Uncategorized
Tagged analysis, arc de trimphe, automatic, elcovision, paris, point cloud
Stone Barn at Morven Park
Below is a composite elevation of a portion of the stone barn at Morven Park in Leesburg, VA.
Composite Elevation with two of the three images faded to 50% opacity
The “elevation” is actually a composite of three images, each rectified to respect the scale of 1:48 (or a quarter inch equals a foot) when printed at 300dpi. The individual images are posted below.
partial elevation (LEFT) qtr scale at 300dpi
partial elevation (CENTER) qtr scale at 300dpi
partial elevation (RIGHT) qtr scale at 300dpi
Below is a screen shot of a point cloud in autocad that shows the exterior of a stone barn. I’ve found that the density of points has a strong correlation to the content of the photos. In this case, we see that the stone surfaces create a very high density while the painted doors and such read almost not at all.
Screen Capture of point cloud derived from photographs of the stone barn at Morven Park, as viewed in Autocad 2011 software
Posted in Uncategorized
Tagged elcovision, Leesburg, Morven Park, mosaic, Orthophotography, Photogrammetry, point cloud, rectified photography, stone barn, true color
Documentation of a sculptural element using Photogrammetry
Test subject
In August I shot a variety of sculptural objects with a mind towards testing the capabilities of photogrammetric software to create useful point cloud descriptions of objects that are difficult to assess conventionally. This urn represents a little of both – parts of its form is sculptural, organic, non repeating, while parts are more classical or architectural in nature.
- Photo with magnifying glass (or ‘loupe’) in Elcovision software
For this study I processed 72 photographs which consisted of three sets of images: two rings around the urn at 16mm and a half arc at 50mm (spatial constraints made it impossible to go all the way around at 50mm).
- Point Cloud and photo stations (in red)
60,000 points were generated to describe the urn itself. When viewed orthographically the point cloud behaves like a drawing – or can be the basis for a measured drawing. The sculptural relief of the figures still escapes precise documentation in the point cloud, I think. Laser scans still do this fine detail better, it seems. But this point cloud – even as it is – in combination with the photographs do so much more than what photogrammetry was able to do even a year or so ago. I think its catching up to laser sourced point clouds and doesn’t require the huge equipment investment.
- Orthographic View of Point Cloud
 
LOCATION
SURVEYING EQUIPMENT ON-SITE TIME COMPLETION TIME FINAL PRODUCT Kłodzko, Poland ZF imaginer 5003; Leica TCR 405 3 days scanning 2 per; 2 days control points survery; 4 weeks 1 person Elevations CAD drawings
Point cloud image 
Point cloud in RGB 
Registered point cloud 
Elevation drawing in pdf |
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