The document discusses digital photogrammetry techniques for capturing 3D spatial data of structures and objects. It notes that photogrammetry using consumer cameras and computer vision offers a high-accuracy alternative to laser scanning in some cases. The text provides details on how photogrammetry projects are conducted, including taking 13-20 photos over 1 hour, analyzing photos based on placing reference marks in overlapping photos, and extracting 3D point data within an hour for quality checking. It also outlines when photogrammetry is a feasible option compared to other methods.

1. Stuart Roberts, HDS Dept.
HOUSTON, TEXAS

2. Digital Photogrammetry

3. Digital Photogrammetry

4. Digital Photogrammetry

5. Digital Photogrammetry
State-of-the-art photogrammetric software systems, use
of consumer digital camera technology and computer
vision techniques, offer an attractive high accuracy
solution when laser scanning is not a option.
Repeatability and image stability has been paramount to
the art of photogrammetry.

6. Different methods can be used.
Three main categories can be distinguished from single photograph,
stereo and convergent.
Reference: GRUSSENMEYER, P., HANKE, K ., STREILEIN, A.
Architectural photogrammetry.

7. Three main categories can be distinguished from single photograph,
stereo and convergent.
Reference: GRUSSENMEYER, P., HANKE, K ., STREILEIN, A.
Architectural photogrammetry.

9. Average project is about 13 to 20 photos. Field collection
takes about one hour to place targets, photograph, and 1
hour to analyze the photos. Larger projects of up to 100+
photos can be performed.
Analyze photos?
In photogrammetry, there is a hard 3X3 rule. The
photography has to be taken in a manner to place a
reference mark on the same spot in three different but
convergent photographs. The next example is an actual
project.

10. DIRECT MEASUREMENTS

12. How quickly can I get my information?
Depending on the complexity of the job and the number of
photos, relatively quickly. 9 photos can be ready in about an
hour. After a QC check, 3D point data can be extracted and
exported.
What is the cost?
The cost is generally 50% to 75% lower than scanning.
Major savings can be attained by not having to ship heavy
equipment associated with scanning. Field time is greatly
reduced.
How accurate is the data?
Overall, photogrammetry is equal or exceeds scanning
depending on clarity and pixel count.
An off the shelf consumer camera can generate data in the
sub-millimeter range.

13. When is it feasible to perform photogrammetry?
Usually, when time is short and space is shorter.
Typically, a small job, like a vessel and few
of tie-in points can be collected by one person.
How big is the equipment?
The camera fits in a backpack with the laptop with a small
package of supplemental targets.
Is it right for every job?
No, it is another tool to collect and display information in
3D.