Classical image of a projected photo on a wall.
Written by David Dengler

Drone for Architecture – Episode 2

I can still remember the day I returned to the office, having spent the better part of a day in the field sketching, measuring, and photographing the as-built conditions for my next architectural project. I dropped the field kit on the floor, placed my digital camera on the desk next to my cell phone and Palm pilot. I turned and went to get a cup of coffee and returned to my desk. After removing the field sketches and notes from my backpack and placing them next to my trio of digital devices, I had an epiphany. My camera, cell phone, and Palm pilot were all digital devices with separate yet important functions. Wouldn’t it be wonderful to have those functions in a single device? Seven years later Steve Jobs made my dream a reality by introducing the iPhone. Thank you! I gave the command and slammed my flip phone shut for the last time…beam me up Scotty.

In 1480 Leonardo da Vinci wrote:

Perspective is nothing else than the seeing of an object behind a sheet of glass, smooth and quite transparent, on the surface of which all the things may be marked that are behind this glass. All things transmit their images to the eye by pyramidal lines, and these pyramids are cut by the said glass. The nearer to the eye these are intersected, the smaller the image of their cause will appear.” (Doyle, 1964)

Leonardo da Vinci continues studying perspective and a device called the Magic Lantern which becomes our modern day slide projector. And with that, we have the birth of Photogrammetry.

Diagram of the photogrammetry process.

Diagram of the Photogrammetry process.

The Definition of Photogrammetry

My favorite definition is the art and science of making measurements from photographs, especially for recovering the exact positions of surface points. The important thing to remember with regard to this definition is that the points are not on a flat plane but within 3D space. Meaning that it is possible, with the proper use of photogrammetry, to create a digital twin, a 3D model that is, of the photographed object.

The diagram above illustrates how the same two points on an object have a comparative relationship that can be calculated and known within 3D space.  The result is accomplished by understanding the positioning of the camera relative to the object.

Now,  if you couple that mathematical magic with a GPS-enabled drone in flight (i.e., the image includes location meta data), you end up with three-dimensional results. Mix in some slick flight patterns with various camera angles and you can capture a massive amount of photographic data quickly. Once the data is fed into photogrammetry software, you can create a digital version of the real world conditions.

Image of the photographic locations above a construction site for photogrammetry use in creating a point cloud.

An Illustration of photographic locations above a construction site
to be used for photogrammetry processing to create a point cloud.

The Goal of Photogrammetry

The photogrammetry process delivers a point cloud – a set of data points in space that are equivalent to the real world – or, a digital twin. Once the point cloud is created, you can do all kinds of magic and produce usable deliverables to a client, or your team.

Deliverables:

  • The Point Cloud itself
  • A 2D Orthomosaic Map – An image file that has been flatten and orthographically corrected to the point cloud. The format is scalable and importable into CAD and BIM applications, typically used for backgrounds or progress reports.
  • Topography and Contour data sets – may also be imported into CAD and BIM applications.
  • Cut and Fill Calculations
  • Volumetrics Calculations. For example, how many yards is a stockpile of aggregate.
  • Accuracy of Earthworks Verification
  • CAD and BIM files for use in applications like Revit. Ready for design professionals to work on projects of all kinds.

Five layers of data derived from drone photogrammetry

Various types of data derived from drone photogrammetry. 

It is important to remember that the point cloud is a 3D standard. Today, we can bring together point clouds from various sources, such as data collected from a drone and ground based LiDAR to create a model that has all of the exterior elements and the interior elements.

Much of this work may still be done manually, but there are teams around the world solving the problem of object recognition and implementing it with AI. The beauty of these technology advances is the speed of processing that delivers accurate data for field verification as projects go vertical. Like the iPhone, photogrammetry with drones can be used for multiple purposes.