Tag Archives: Facade

completed line drawings

Trinity Episcopal Church

Overview of Sheets prepared for Trinity Episcopal Church in Renssalaerville, NY

Drawing with a few rectified images "unfrozen" in the AutoCAD drawing.

Telescoping Tripod

Using my telescoping tripod in Renssalaerville, NY

Using my telescoping tripod in Renssalaerville, NY

Over the summer I started a business venture with a friend doing aerial photography with his 1946 Cessna. I do the photos, he does the flying… Anyway, this experience got me hooked on the possibilities of enhanced points of view.

For a long time I’d thought of the cherry picker (aerial lift/bucket truck, etc.) as my only option and had often worked around the lack of great points of view with creative alternatives when budgets and such would not allow the use of a cherry picker.  But, being hooked as I was, I did more research and realized that a relatively low cost solution was available which could yield surprisingly good results – if you have the guts to put your calibrated camera up in the air on a telescoping tripod.

Even if you purchase a well made tripod with adjustable legs that allow the whole rig to be leveled, and even if you attach guy wires to stabilize everything ( if you have the need plus the manpower), even so, it takes some nerve to put your specially calibrated SLR way up into the air!

Of course its range is nothing compared to a big boom lift, but it can let you see over cars and trucks, and bushes and fences and all sorts of things.  Its just one more trick up your sleeve that can help your work become just a little better.

Technical Elevation Drawings – exterior and interior

Exterior Elevations

Exterior Elevations

Here I am posting a few drawings from a project completed about 18 months ago.  These drawings depict the existing conditions of the Luzerne County Courthouse which is located in Wilkes-Barre, PA. More on the building can be found here.  I prepared these for a team of architects and engineers who were to conduct a survey of these surfaces in preparation for an extensive masonry and stone rehabilitation project.  It is a beautiful building with a grand atrium reaching up through the building.  I also did drawings of this interior space.

Interior Elevations

Interior Elevations

I am posting these to show that, for all the value of rectified imagery, point clouds, three dimensional models – sometimes the most apt documentation is the relatively “old school” approach of using 2-D drawings to depict 3-D conditions through plan elevation and section.  In the end, the documents that I have prepared for clients over the years have had to pass this test: Will these drawings help my team to communicate easily together when assessing and discussing the problems and solutions at hand with a given building?  Will these drawings help me to accuractly assess the scope of work involve – and, will I beable to use them to communicate with and direct the contractors in the field who are doing the actual work to the building?

Earlier this week I was giving a presentation to students at the University of Virginia.  I started off showing them work that I did 15 years ago when everything was more or less analog in nature, later showing how fantastic it is now to be able to merge raster and vector data together digitally. And then I thought of these drawings and how deftly drawings can handle such complex forms with precision and efficiency.  As an industry, we are doubtless moving towards wider use of three dimensional modeling and Building Information Modeling (BIM) – yet I admit to having a fondness for the “old school” approach that I cut my teeth on, so to speak.

View of building exterior

View of building exterior

View through atrium to dome

View through atrium to dome

Mosaic Images from multiple view points simultaneously

Maria Mitchell Hybrid Drawing

Maria Mitchell Hybrid Drawing

Above is what I like to call a “hybrid drawing” of the historic Maria Mitchell House located on the island of Nantucket. A hybrid drawing is one of two things, or possible both: It is a photographic image that behaves like a measured drawing (it is scalable and can provide quantifiable data), or it is a measured drawing that is rich in the way a photographic image is (materials, colors, actual as-found existing conditions are depicted photographically).

Line drawing with key to individual rectified images

Line drawing with key to individual rectified images

Above is a view of the line drawing with all of the rectified images that compose the hybrid drawing “frozen”. In other words, in the CAD drawing, these layers of information are turned off and made invisible so as to see just the line-work itself and a series of polygons that correspond to bit map/raster images that are referenced by the drawing.

Below are a series of images showing each individual rectified photographs as it is situated in the context of the drawing.  These added together make the composite image at the top of this post.

Maria Mitchell 10Maria Mitchell 9

Maria Mitchell 8Maria Mitchell 7Maria Mitchell 6Maria Mitchell 5

Maria Mitchell 11

Franklin & Marshall Exterior Survey

Old Main at Franklin and Marshall

Old Main at Franklin and Marshall

Last spring I did some work at Franklin and Marshall College in Lancaster, PA.  I prepared a combination of measured drawings in CAD linked  to rectified photographs of the three oldest structures on the campus. These were then used as base documentation for an assessment of the existing conditions of the masonry surfaces across the extent of these buildings’ exterior facades.

The sequence of this work went roughly as follows:  I first shot photos of all of the buildings from points of view available on the ground (using a specially calibrated digital SLR).  Back in my offices in Virginia I used photogrammetric software to “back calculate” the camera stations and to make precise 3-D measurements of points on the three structures.  I used this dimensionally accurate point cloud as a reference to create rectified photographs of the surfaces visible from grade.

F and M Old Main Rear Elevation

F and M Old Main Rear Elevation

Using the point cloud and the rectified photographs I then created measured line drawings of the structures and laid them out onto tabloid size sheets for use in the field.  These were taken by hand up into an aerial lift so that conditions could be noted with a fair degree of accuracy once assessment were made both visually and manually.

tabloid size field sheet with notes

tabloid size field sheet with notes

Once the assessment was completed the data recorded on the field sheets was entered in the CAD drawings.  At this point the line drawings in CAD were enriched by a mosaic of rectified photographs visible inside of AutoCAD.  This allows for an accurate transfer of notes from the field to eventual construction documents.  A sketch of an area or region can be transferred to CAD and become dimensionally reliable.  This is a very important step because it provides for an accurate tally of areas to be treated in one way or another.

aerial lift

aerial lift

Since the main structure was rather tall, I also returned to the site to go up in the aerial lift to collect more photographs to further enrich my drawings with better rectified images of areas that were either blocked by vegetation, neighboring buildings, or were too foreshortened to provide good rectified images.

F and M Old Main Rear Elevation with photos

F and M Old Main Rear Elevation with photos

Photogrammetric Analysis

Photo with reseau and digitizing puck

Photo with reseau and digitizing puck

Analyzing stereo-pairs of photographs is a matter of locating the same precise point as it is captured in two or more photographs. In the old days, this meant using a digitizing puck to magnify and locate the x,y location of a point (relative to a set of cross hairs that were essentially coplanar to the film).  Today, with digital photographs, it is a matter of specifying pixels.  In both cases, a handful of these comparison points is needed to construct a geometric model for each camera station: each point becomes the terminus of a theoretical “ray” that passes through the focal point of the lens.  When the precise nature of how light passes through the focal point of the lens onto the film plane (or digital sensor) is understood mathematically, then this geometrical model can be quite precise, allowing for an accurate “back calculation” of the relative relationship of the camera from on photo station to another.

Its uncommonly difficult to write about – when you see it “happen” it is a little easier to understand!

wire frame diagrams of point cloud and camera stations

wire frame diagrams of point cloud and camera stations

Today, this whole process is becoming more and more automated, allowing for the creation of very rich point clouds when needed – or quickly creating smaller “smart point clouds” when the goal is a vector line drawing of a building, for example.

Photogrammetry and Stereoscopy

Ocean City City Hall (Left)

Ocean City City Hall (Left)

Ocean City City Hall (Center)

Ocean City City Hall (Center)

Here are two photographs from a project that IAT completed at the Ocean City City Hall in Ocean City, NJ.  These were shot using a Leica R5 which had been modified for use for photogrammetry. A thin glass plate with an array of cross hairs was inserted between the focal point of the lens and the film.  This was required for a good camera calibration. (Nowadays with digital SLR camera bodies the cross hairs – or the “reseau” – is no longer required.)

The basis of photogrammetry is “stereoscopy”, or simultaneously viewing the same subject matter from two vantage points.  So these two shots capture the same facade from positions to its left and center.  They are not shot simultaneously in fact, but sequentially – but in the life of a building they reflect more or less the same instant in time.

Additonal photographs from yet more unique camera locations can be included in a photogrammetric study, so in fact this technique goes well beyond stereoscopy which, technically, is limited to only two views. But for the sake of understanding what is happening in photogrammetry more easily I’ll only talk about two or three views for the moment.