Tag Archives: Photogrammetry

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.

Three Structures at Morven Park Documented

Morven Park Barn Complex

Above and below are screen shots (from AutoCAD) showing a group of rectified images assembled into model space depicting the existing conditions of one of three separate structures recently documented at Morven Park in Leesburg, VA.

Morven Park's Corbell House

For this project, the “drawings” are really a series of boundaries to rectified imagery organized onto different drawing layers.

Farm Manager Residence

All of the rectified images shown have been desaturated in order to make them read more clearly. Color versions are also provided.

War Memorial Auditorium (Progress)

War Memorial Auditorium - Nashville, TN

Earlier this month I travelled to Nashville to shoot photos of this gorgeous classical structure erected by the State of Tennessee, the City of Nashville and Davidson County in 1923 (immediately following the first World War). Nashville Architect Edward Dougherty won a Gold medal for the design from the AIA in 1925. From 1939 to 1943 the building served as the fourth home to the Grand Old Opry and witnessed the induction of Roy Acuff, Bill Monroe, and Minnie Pearl.

Today the War Memorial Auditorium is still in use as a music venue as well as offices for the State of Tennessee. To support an effort to preserve the building I am preparing measured drawings to cover the all of its exterior envelope. My line drawings will be enriched with rectified photography. Here is a sample (in progress) of a courtyard elevation.

Courtyard Elevation (in progress) in AutoCAD drawing software

Here are two more screen shots that show some of the rectified photographs (on separate drawing layers) that are “thawed”:

In progress DWG file with 2 of 4 layers bearing rectified photography thawed

In progress DWG file with remaining layers bearing rectified photography thawed

In the end, my drawing set will be organized across at least eight E sized sheets prepared for plotting at 1/4″=1′-0″ (or 1:48) .

If you want to see the drawings completed, stay tuned/subscribe!

New page about furniture design collaboration

There is now a new page describing  an interesting collaboration with a San Francisco based furniture designer this past summer. Here is a link.

Table by Ryan Wickre of Fixed Design

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.

As found drawings

"As Found"

There is a distinction between “as found” drawings (drawings that depict the reality of an existing building as it is “found” today) and drawings that were “found” in a search to locate historical documentation about a building. This is not to knock the value of original drawings that are sometimes available when working on an historic structure. Its just a reminder that original drawings do not always provide accurate descriptions of what was built. Depending on when and how the building was constructed, design drawings sometimes were more like polite suggestions.

The other issue with “found” drawings is how they are converted into CAD drawings or BIM models. Care must be taken to avoid a messy foundation for preservation work.

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

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

 

A New way to use Photogrammetry (as a design tool)

Wireframe model projected accurately back into photograph

Typically I use photogrammetry to measure and draw existing structures.  Recently I’ve started using it also to visualize new structures. The photo above shows an image that was used originally to create a set of measured drawings of an existing house.  Once I had those drawings completed I designed a new structure to be built above the foundation of an existing garage.  I made a simple 3-D model of the new design and then accurately projected the model back into the photograph. This has been an invaluable tool in getting my client to understand the new design.

Alternate View

More on this new way of working to come…

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