Tag Archives: rectified photography

A Comparison of Orthophotography and Mosaics of Rectified Photographs

In 2012 I prepared documentation of the masonry surfaces of this historic room in the Maryland Statehouse. This documentation provided a baseline of the existing conditions to allow for an investigation into how exactly the room was appointed in its heyday – when Thomas Jefferson was named ambassador to France etc…

The documentation that I created consisted of measured line drawings (in CAD format) augmented by a mosaic of photographs that had been rectified to match the real world size and shape of the various portions of masonry. here is what it looked like:

Measured Line Drawing

Measured Line Drawing

The image above ^ shows a screen capture of an accurate measured line drawing delineating the limits of the masonry surfaces and indicating the architectural features nearby.

Key to regions/individual rectified photographs

Key to regions/individual rectified photographs

This image ^ shows a drawing layer “thawed” to display a sort of key plan to the different regions of masonry for which individual rectified photographs were prepared. The next few images show some of the drawing layers containing these rectified photographs “thawed” and you can get an idea of how the composite whole is constructed like a mosaic.

A few rectified photographs thawed...

A few rectified photographs thawed…

a few more rectified photographs thawed...

a few more rectified photographs thawed…

A single rectified photo of the entire wall

A single rectified photo of the entire wall

So, the above image ^ shows how the entire wall could be captured, rectified, and brought into the measured drawing. (The reason that the other images were created in “panels” was to provide for two things: (1) enhanced resolution for the individual photographs, and (2) the ability to “see around” obstacles presented to a single point of view. For example, in the image above, portions of the masonry surface are obscured by some of the architectural detailing/millwork)

Below is a “zoomed in” version showing this condition in higher detail…

When a single image is rectified so that the masonry portions of the image match the real world size and shape of what is being depicted, features that are NOT co planar can be distorted, not matching real world conditions. This is one reason a mosaic approach was needed to cover all of the surfaces in question  accurately.

When a single image is rectified so that the masonry portions of the image match the real world size and shape of what is being depicted, features that are NOT co planar can be distorted, not matching real world conditions. This is one reason a mosaic approach was needed to cover all of the surfaces in question accurately.

So, in this approach, the line drawings carried the responsibility of delineating the wall’s size, shape and configuration of architectural elements while the rectified photos carried the responsibility of conveying the lay out and character of the masonry construction units.

Today, I might approach the project differently, using a true “Orthophoto” of the sucrose instead of a mosaic. The distinction is important. An Orthophoto is a planar projection of a dense point cloud or textured mesh 3D model. I was unable to create these back in 2012 when I did this work – but today I can do so -still using photogrammetry- and maintain the same level of accuracy demanded by such work.

An Orthophoto (constructed from images from various points of view) depicts the masonry surfaces as well as the architectural detailing/millwork accurately.

An Orthophoto (constructed from images from various points of view) depicts the masonry surfaces as well as the architectural detailing/millwork accurately.

This image ^ shows the orthophoto seated nicely behind the measured line drawings. As mentioned above, it is a projection from a 3D model, which can be looked at from a variety of angles and manipulated in 3D modeling software . below is a video clip showing the model these surfaces.

I am really excited to have this new set of tools at my disposal! The mosaic approach is still sound and may be more appropriate for some projects. In fact, the two approaches can coexist in the same set of documentation if needed. But the addition of 3D scanning and the creation of true Orthophotos to my toolbag will allow me to provide architects and engineers faced with complex preservation challenges with more options.

West Wall of the Old Senate Chamber - Orthophoto

West Wall of the Old Senate Chamber – Orthophoto

more background info here:

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Tall Structures and Focal Lengths

The Carillon in Byrd Park - Richmond, VA

The Carillon in Byrd Park – Richmond, VA

I am going to share a quick study I did of the Carillon in Richmond’s Byrd Park and use photographs of this tower structure to demonstrate how different lens focal lengths can work together to access a structure when it is freely accessible (visually) from points of view on grade. In essence, I am trying to answer the question from one of my clients who asks “what kind of resolution can I expect to get for rectified photography of a tall structure (up to 200′ high)?” -and, correspondingly, “what kind of access would be required to obtain these photos?”

So, for starters, the photograph above was shot with a 40mm lens on a full frame DSLR about 250′ back from the face of the tower. It serves to capture the entirety of the structure – but not with particularly high resolution once you “zoom in”, see below:

crop on 40mm shot "zoomed in"

crop on 40mm shot “zoomed in”

Below is a diagram that shows the position of the camera and image capture relative to the tower both in side view and front view.

c40-132

In order to gain sufficient resolution to clearly see the architectural features and construction units with a lens this length on must position the camera a lot closer to the structure – more like 50′ or so away, such as is shown here:

c40-18

This yields a photo that obtains a desirable level of resolution in terms of detail, but only covers a portion of the overall surface. Below I’ll post the “close range”  photo before and after rectification and then I’ll post an additional image that shows something closer to a “100% crop” of the rectified image (since these images are much reduced in size) .

40mm shot ~50' from surface

40mm shot ~50′ from surface

40mm shot ~ 50' from surface - rectified to principal plane

40mm shot ~ 50′ from surface – rectified to principal plane

Detail of Rectified Photo showing a sufficiently rich image resolution to document architectural elements in elevation

Detail of Rectified Photo showing a sufficiently rich image resolution to document architectural elements in elevation

So, in order to cover the fell extent of the tower’s surface, one needs to tak a multiple of images from a variety of points of view and blend them together as a sort of mosaic of rectified images which can be collectively tied together by a measured line drawing.

d118

Shooting overlapping photos from different points of view is easy enough, as we move around the structure laterally… But how do we maintain this level of resolution VERTICALLY? Some answers to this question include gaining higher points of view for additional photographs by using scaffolding, an aerial lift/cherry picker, shooting from an adjacent structure, even a remote controlled helicopter/drone etc… These are each workable solutions – but each carry additional complications and costs. Sometime these types of solutions are required because space around the structure is limited (imagine a tall building on a narrow street in Manhattan). But if a structure is sufficiently free standing, a consistently adequate level of resolution can be obtained by moving away from the building and shooting photos using longer focal lengths. In such cases this can be a very cost effective solution.

The question, then, is how far away do you have to go and what focal lengths need to be used?

Below I’ll post a number of diagrams similar to the one shown above that each include a 200mm expo taken at a variety of distances from the structure.

200mm shot ~400' from structure

200mm shot ~400′ from structure

200mm shot ~200' from structure

200mm shot ~200′ from structure

200mm shot ~75' from structure

200mm shot ~75′ from structure

I tried to shoot the same masonry surface in each case – the center being roughly 150′ or more above grade. In the diagrams’ side views you can see how the amount of foreshortening increases with shots closer to the building. This will be apparent both in the un-rectified shots as well as the rectified shots, shown here:

rectified image from a 200mm shot taken ~75 from the structure

Rectified image from a 200mm shot taken ~75 from the structure

detail of rectified image from a 200mm shot taken ~75 from the structure. Very pronounce foreshortening  and resulting distortion of elements no coplanar with principal place.

Detail of rectified image from a 200mm shot taken ~75 from the structure. Very pronounce foreshortening and resulting distortion of elements no coplanar with principal place.

rectified image from a 200mm shot taken ~200 from the structure

Rectified image from a 200mm shot taken ~200 from the structure

detail rectified image from a 200mm shot taken ~75 from the structure showing much less distortion.

Detail rectified image from a 200mm shot taken ~75 from the structure showing much less distortion of non co-planar elements.

detail from a rectified image from a 200mm shot taken ~400 from the structure. Distortion is reduced even further but distance from the structure starts to have an effect on the image's resolution.

Detail from a rectified image from a 200mm shot taken ~400 from the structure. Distortion is reduced even further but distance from the structure starts to have an effect on the image’s resolution.

In the last image, one can see how as the camera moves away from the building the distortion continues to be mitigated -but the resolution of the image starts to suffer. So, as you move away from the building you have to increase your calibrated focal length in order to maintain a desirable resolution.

Below, I’ll share a number of “slides” that try to summarize what I’ve been trying to describe. Each shows a plan view of the Carillon along with a front and side diagram at the lower corners, with a snap shot of the image captured in the upper left corner. First, two 40mm shots and then a batch of 200mm shots getting progressively  closer to the building.

40mm 50' from building

40mm 50′ from building

40mm 220' from building

40mm 220′ from building

200mm 500' from building

200mm 500′ from building

200mm 400' from building

200mm 400′ from building

200mm 320' from building

200mm 320′ from building

200mm 250' from building

200mm 250′ from building

200mm 200' from building

200mm 200′ from building

200mm 100' from building

200mm 100′ from building

200mm 75' from building

200mm 75′ from building

In fact, this method involves trade offs, as I mentioned in the captions above… I think the most successful arrangement are the shots at about 200′ away – they combine a reasonable amount of “distortion reduction” while maintaining sufficient resolution without having to move too far away from the building. This can be important (not having to go too far from the structure) when shooting tall structures that are adjacent to water or a similar obstacle such as one would finde when shooting LIGHTHOUSES (see below). At 200′ from the building sufficent visual access should be available without the need to rent a boat, even for the bayside of the Cape Lookout Lighthouse.

Cape Hatteras Light

Cape Hatteras Lighthouse

Cape Lookout Lighthouse

Cape Lookout Lighthouse

The Carillon at Byrd Park.

The Carillon at Byrd Park.

Cosmos Club Ball Room

just a quick post to share some images from a project completed in 2010. I understand that the restoration of the ballroom is fully complete now.

Ceiling of the Cosmos Club Ballroom

Centerpiece of Ballroom ceiling

Detail

Elevation of Cosmos Club Ballroom

a closer look...

...and a little closer

In these elevation drawings won can see black lines overlaid atop the rectified images. These are dimensionally accurate vector lines in AutoCAD.

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

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

Additional content added

Today I updated content of the following pages:

Starting to fill in content to this site

I’ve started to add content to this site now that its structure is more or less laid out. I’ve added sample photographs to the Photography|Travel section

Plus I have added content to these projects:

New Header

I’m posting a new header for this blog. It’s a composite image of half of the Quai Vauban facing the river Doubs in Besancon, France.  It’s an accurate assembly of a couple dozen images that are each rectified to a known plane/scale.  Here is a detail showing the resolution of the image. We are hoping to see this printed full size and used as a mural somewhere in Charlottesville – a sister city to Besancon.

287 Broadway

Building at Broadway & Reade Street in Manhattan

“Prominently situated on a comer site, the 287 Broadway Building is notable for its combination of the ltalianate and French Second Empire styles as executed in cast iron, and one of the few surviving examples in New York City.” – From the 1987 NYCLPC Landmark Designation Report

Construction of a new building to the south of 287 Broadway has caused this historic structure to fail.  I was asked to prepare rectified photography and a point cloud file/drawing that will at once capture the existing conditions and composition of the cast iron facades – and to provide some precise measurements as to how severly the building is leaning and in what manner.

Reade Street Elevation

Broadway Elevation

Two elevations of 287 Broadway

Point identities (that correspond to a "smart" point cloud) are noted on the Photographs