Tuesday, December 30, 2008

Laser Scanning Versus Photogrammetry

At the end of my previous post I asked which is more applicable for 3D cultural heritage projects, photogrammetry or laser scanning?

HDS6000 Laser Scanner

A reader pointed me in the direction of the December issue of Geoinformatics, which features an article on page 50 called "3D Laser Scanning and its 2D partners". I wanted to highlight the article in this post as it offers some interesting thoughts on the subject. In particular the article makes the following points (with my own observations):

  • There are similarities between photogrammetry and laser scanning. For example, both technologies are used to capture point clouds where points have XYZ coordinates. I would add that the differentiator is that in photogrammetry we are usually capturing points to model a surface (e.g. a TIN or grid) as opposed to a true 3D point cloud (e.g. multiple points with the same XY but different Z's).
  • Challenges in the adoption and acceptance of laser scanning, being the (much) more recent technology. For example, the cost and learning curve. I agree with this, however as the authors note this is changing. We face the same challenge in photogrammetry, which still carries a bit of a stigma as a dark art within the broader geospatial community. However times are changing and new technology will continue to flatten out the learning and cost curves...
  • The all-too-common belief that the two technologies compete. The authors argue that this is a misconception and go on to outline why photogrammetry and laser scanning are complementary. I completely agree with this point: both technologies have advantage and should be implemented as needed on a case-by-case basis. I think we're seeing this in the context of the airborne mapping world as well - an increasing number of organizations are opting for optical and LIDAR systems for simultaneous collection. The Leica RCD105 Digital Camera is a good example of this, as it is typically sold alongside an ALS LIDAR system. There are a lot of advantages for such a system but that's a story for another post.
The article then proceeds to discuss laser scanning in the context of recording historic monuments and landscapes, along with several projects (including Cyark) and examples. Overall it is a compelling read and I'd recommend picking up a copy or checking out the online version if you are interested in this topic.

So in summary, I suppose the question above needs to be turned around. For recording cultural heritage, choose the tool set that best fit the requirements - which may mean integrating several technologies.

1 comment:

Jarlath said...

One of the most compelling reasons to acquire LiDAR is the ability to apply automated routines to extract information. When you combine the spectral information contained in a digital orthophotograph with the structural information in LiDAR one has a powerful dataset from which to map the earth's features. I agree with your statement that photogrammetry and LiDAR are complementary, but would take it one step further and say that acquiring the two is almost a necessity if you want to be able to perform broad area mapping in a cost efficient manner.