Category Archives: photogrammetry

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

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Stone Barn at Morven Park

Here I am posting 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 1:96 (or a quarter inch equals a foot) when printed at 300dpi. The individual images are posted below.

partial elev left qtr scale at 300dpi

partial elev center qtr scale at 300dpi

partial elev right qtr scale at 300dpi

Screenshot

I’ve been too busy to post a lot of little projects that were in the works at the end of the summer. They’ll have to trickle in unless they get displaced by new projects… I’m just happy that there are projects! This post is just to share 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.

Test Project: Marquis Building

Angle View of Building

In between wrapping up summer projects and starting some new ones,  I wanted to work on my technique with Elcovision’s powerful new module that allows dense point clouds to be extracted from photographs.  I chose the “Marquis Building” on Beverley Street in Staunton for fairly obvious reasons. (In fact there it is at the top of this page on my mast head – from was a two dimensional rectification of the entire block)

Left Photo

(Note: I used considerably more photographs than just these three shown here)

Right Photo

Over the summer I did some training in Switzerland on how to use the new software module – but I did not have access to all of my regular equipment.  So this test project was the first time I had a chance to enhance my ‘overlap coverage’ by the use of a telescoping tripod.

The point cloud created from the analysis phase is dense enough to provide a quick sort of three dimensional model of the building even without any additional drawing.

In Elcovision – or AutoCAD for that matter – one can “hover” around the point cloud and take snapshots in either perspective or isometric views.

Plan View of Point Cloud

True Color Point Cloud

Point Cloud of Staunton Creamery Building

Here I am posting a point cloud scan of a structure much more mundane than the Arc De Triomphe, a square-ish two storey building located not far from my office.  This was produced from about 40 photographs and consists of tens of thousands of point measurements that are represented in their true color.

Staunton Creamery

Point Cloud Scan of L’Arc de Triomphe

L'Arc de Triomphe - Paris

I shot a series of photos around the Etoile at the center of which stands this grand monument.  It is incredible how busy the traffic is here at all hours, both vehicular and pedestrian! Anyway, from this series I was able to generate a point cloud to describe this massive arch at the head of the Champs Elysee. I then scaled the entire affair based on measurements taken from Google Earth.

Point Cloud Scan of Elevation

I also shot the ‘undercarriage’ of the monument to create a point cloud describing the vaulted surfaces there using photogrammetry. The point cloud itself is dense enough to create a sort of drawing. The location of any additional points – or edges etc. – can then be easily (an accurately) queried directly from the photographs.

Photos of the surfaces underneat

Point Cloud of surfaces underneath

Reflected Ceiling Plan of the Arch's central bay (point cloud)

Point Cloud Scan of Column Base using Photographs / Photogrammetry

Point Cloud Scan of Column Base

My second sample project using photographs to create dense point clouds to describe a non orthogonal object used a column base from the cathedral de Saint Pierre de Geneve.  These stone surfaces proved to be easier to capture than the sleek, reflective brass surfaces o the sculpture in my previous post.

This point cloud was created with a series of a half dozen photographs shot in an arc from left to right around the subject matter.  We can see here that in oreder to get all of the surfaces adequately rendered, one needs to also change the height of the camera’s point of view.

As it is, the point cloud consists of over 15,000 points. The points can be imported directly into AutoCAD with their true colors and manipulated there to be transformed into a surface model – or simply as the basis for a measured line drawing.  As for accuracy, 75% of the point measurements (which would include virtually all of the measurements describing the subject close at hand) are accurate to less than 1/8″.  Half of them are more accurate than 1/16″.

Here is a photograph of the column base, followed by two more views of the point cloud:

Column base at the Cathedral de Saint Pierre de Geneve

Plan View of the Point Cloud

Side View of the Point Cloud

Reclining Figure Arch Leg – Sculpture by Henry Moore 1973

Reclining Figure Arch Leg – by Henry Moore 1973

This summer (2010) marks the real debut of a reliable automatic generation of dense point clouds by using photogrammetry.  I travelled to Switzerland in July and gave this exciting new software module a try on something that would be a real challenge to document in anyway other way – a sculpture by Henry Moore.

The four panels below show different views of the point cloud generated from these photographs. For me the real lesson in this study is that objects to be documented in this way need to be photographed in conditions that produce as even lighting as possible. One can see that some of the reflectiveness from the metal (brass) surface of the sculpture resulted in less-dense-than-desired regions in the point cloud. Still, I was excited to see how well it performed under what I now understand to be relatively harsh conditions.

The density of these point clouds is considerably higher than what photogrammetry ordinarily would produce while not being the hard-to-manage overkill produced by laser scans. what’s more, these point clouds can be enriched with the same type of smart point clouds that provide a meaningful link to both rectified photography and architectural description.

GUM

GUM Department Store - 35 Sveltanskaya Street (Vladivostok)

Here is one of the first photos I shot when I arrived in Vladivostok. It show the State Department Store known as “GUM” located on Sveltanskaya Street in the center of the historic city. More info can be found here.

After a couple weeks it looks like my project here will move forward after all!

Belmead on the James

Belmead on the James

Yesterday I visited an incredible historic site in Virginia that I had been totally unaware of: Belmeade on the James. An incredible Gothic Revival house that has remained fundamentally unaltered for over a hundred years (It was designed and built in the 1840’s and had an addition fifty years later). Here is a link to a good article about the property and its future.

I hope to be able to help keep this building and its grounds alive, functioning and available to the public.