Photogrammetry vs 3D Scanning

Digital 3D models are used in a variety of industries, but there is more than one method to create them from a real object or scene. Photogrammetry and 3D scanning are the two primary methods for creating these models. Whether you need 3D models for design, manufacturing, forensics, or research, below are the pros, cons, and differences between the two methods.

3D Scanning

When comparing 3D scanning to photogrammetry, two varieties are most common – laser and white light 3D scanning. Laser scanning uses a laser to measure an object’s geometry and create the model through the data obtained. The laser beam is swept across the surface, and the device uses angle encoders of the beam projector and the return “time-of-flight” to calculate the location of each point in 3D space. Once all of the points are captured and recorded, a dense point cloud results. To capture a complete object, the laser scanner or object is moved, and the scan repeated. Optionally, additional software can connect the points to create a polygonal mesh for 3D modeling and design purposes.

White light 3D scanning utilizes a projector (often LCD) and one or more cameras to map an area or object. Light patterns are projected onto the surface, and the camera then records the surface by measuring where and how the light deforms around it. To ensure every angle is captured, the scanner is moved around the object, or the object is moved in front of the scanner. The result is a point cloud similar to what laser 3D scanning produces, with the same option of producing a polygonal mesh.

Pros & Cons of 3D Scanning

3D scanners have several advantages, primarily, their high accuracy and high resolution. This method performs well for smaller parts and can create data points in real-time. This can save time, as you’ll see what areas need to be rescanned or have been missed before taking it into the design phase.

However, light interference can produce unfavorable 3D scans. Both laser and white light scanners read light sources to collect the data. If there’s too much ambient light the collected data may be distorted. Because of this, 3D scanning is best used where the lighting can be controlled. Similarly, 3D scanners also have trouble with shiny or reflective surfaces. These surfaces tend to send the light away from the input sensors making getting a quality scan difficult.

One of the biggest disadvantages of 3D scanners is the price. The machinery can cost tens of thousands of dollars. As technology advances, you’ll need to purchase new scanners to keep up. Another disadvantage is the size and transportability of the device.

Photogrammetry

Photogrammetry is another method used to create 3D models. Instead of using active light sources, this technology uses photographs to gather data. Unlike the expensive machines needed for 3D scanning, photogrammetry only requires a camera of your choice, a computer, and specialized software.

 

To create a 3D model using photogrammetry, photos are taken from a variety of angles to capture every part of the subject with overlap from picture to picture. This overlap is necessary for the software to align the photos appropriately. Once all of the images are taken, they’ll be imported into the photogrammetry software, which aligns the pictures, plot data points, and calculates the distance and location of each point in the 3D space. The result is a 3D point cloud that can create a polygonal mesh, just like 3D scanning.

There are three methods of using photogrammetry: manual, target, and dense matching.

  • Manual: The manual method of photogrammetry is the slowest and generates a low point count. Though it’s not the best for every task, it does allow you to capture exactly what you want. Here the operator identifies like-points across photos.
  • Targets: The target method is automated and much faster, producing a higher point count. There is a bit more set up time involved, but it is incredibly accurate.
  • Dense Matching: The dense matching method is the most similar to 3D scanning, generating dense point clouds that can be used in a variety of applications.

Pros & Cons of Photogrammetry

The main advantage of using photogrammetry over 3D scanning is price and accessibility. A camera and photogrammetry software are usually less expensive, and much easier to transport!  You might already have a camera as well (often a mobile phone camera will work).

Another important advantage of photogrammetry is its ability to reproduce an object in full color and texture. Though some 3D scanners can produce this as well, photogrammetry is the method to use when you’re looking for realism. 

Lastly, an interesting advantage is that photogrammetry can work at many scales and sizes. You can model the tip of a finger or a whole mountain range. Other 3D scanners are limited to a particular sized object.

Photogrammetry has its disadvantages. When using the scanning method, as described above, texture plays a big part in how the reference points are made, working with smooth, flat, or solid-colored surfaces can be difficult. There are a few ways to counteract this, but they may be cumbersome or not available. Photogrammetry projects can sometimes involve more in-office processing time as well.

How to Know Which Is Best?

3D laser scanning and photogrammetry are excellent in their own ways. When deciding which is the best match for your needs, you want to consider your budget, the size of the area, and the level of accuracy you need.

For example, when you need to render a landscape as a 3D model for an archaeological survey or for movie graphics, photogrammetry is the route to take. Since capturing the realism of the scene is most important, photogrammetry will provide better results overall compared to 3D scanning.  Or if you want very high accuracy of specific points in your scene or on your object, photogrammetry with targets is the best, and maybe, the only choice.

3D scanning is suited to dense cloud capture of surfaces with little texture. 3D scanning is useful for capturing very large detailed areas.

You can use the two together for specific applications. To solve a case, a forensics team may need to analyze security footage to determine what happened. The camera itself can only capture so much, but by utilizing 3D scanning and photogrammetry, a 3D model can be created and key evidence extracted from the security footage.

Photogrammetry with PhotoModeler

Photogrammetry compares to 3D scanning primarily in its third method (dense matching) – which means photogrammetry offers more capabilities overall. Though laser or white light scanning is useful for capturing objects very quickly to high detail, it is expensive. Anyone can use photogrammetry with a camera, a computer, and our exceptional software at PhotoModeler. Contact us today at 1-778-370-3063 or visit our FAQ page for more information.

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