Photogrammetry and lasergrammetry have been discussed one after the other in the previous chapters of the text. It can be useful to compare them (see also [GRU 08, AND 13, RAS 13]) and to show an example of how these two techniques benefit from being used together. Only the phases of data acquisition and production will be addressed here, the cloud point processing phase is discussed in detail in Chapter 5, and remains mainly unchanged regardless of the source of the data.
The two techniques described above can be compared from different viewpoints:
– Equipment: the average equipment used for laser digitization is more expensive than that used for photogrammetric surveys. The logistics that are required to use a laser scanner are also more burdensome (equipment can be heavy and needs an electricity source). Moreover, the data acquisition process with laser scanners is quite long (compared to the almost instant photogrammetric process), and it is therefore essential to work on perfectly stable ground. The cameras which provide the photogrammetric information of the site can be easily used with a number of different devices (masts, poles, ground-based and airborne vehicles) in order to tackle any possible site layout.
– Lighting and rendering: lighting is a delicate matter for photographic images, whereas laser digitization could theoretically be carried out without ...