The number of points that are generated during step 2. Point Cloud and Mesh depends on several factors such as the image size, image content, image overlap, and processing options. Therefore, it is not possible to precisely estimate the number of points generated during step 2. However, some statistics about the number of points of the point cloud could be made and are shown below.
Estimated number of points observed in projects with 14 MP images
The used options for step 2. Point Cloud and Mesh:
- Image Scale is 1/2 (Half image size).
- Point Density is Optimal.
- Minimum number of Matches: 3
| Number of images | Number of points | LAS file size |
|---|---|---|
| 250 | 20 - 50 million | 0.3 - 1.0 GB |
| 500 | 40 - 60 million | 1.2 - 1.9 GB |
| 1000 | 80 - 120 million | 2.5 - 3.8 GB |
- The size of the LAS file depends on the number of points. One point will take 34 bytes disk space.
- The above-mentioned numbers are only estimates and depend on the image size and content. For example, urban areas projects will have more points than desert or snow area projects.
Estimated impact of processing options on the number of points generated
There are 2 processing options for step 2. Point Cloud and Mesh that have an impact on the number of points generated:
- Image Scale
- Point Density
For more information about the processing options: Menu Process > Processing Options... > 2. Point Cloud and Mesh > Point Cloud.
The following table summarizes by which factor the number of points obtained with the default options changes when changing the Image Scale and Point Density.
| Image Scale \ Point Density | 1 (Original image size, Slow) |
1/2 (Half image size, Default) |
1/4 (Quarter image size, Fast) |
1/8 (Eighth image size, Tolerant) |
|---|---|---|---|---|
| High (Slow) | x16 | x4 | Same as default | ÷4 |
| Optimal | x4 | DEFAULT | ÷4 | ÷16 |
| Low (Fast) | Same as default | ÷4 | ÷16 | ÷64 |
| Image Scale \ Point Density | 1 (Original image size, Slow) |
1/2 (Half image size, Default) |
1/4 (Quarter image size, Fast) |
1/8 (Eighth image size, Tolerant) |
|---|---|---|---|---|
| High (Slow) | 640 million | 160 million | 40 million | 10 million |
| Optimal | 160 million | 40 million | 10 million | 2.5 million |
| Low (Fast) | 40 million | 10 million | 2.5 million | 0.625 million |
Does the Image Scale affect the quality of the point density? Will I get better accuracy if I process at Original Image size set on Optimal as opposed to 1/2 Half Image Size set on High? The output point densities are the same and the time to process is the same.
Hi Derek,
You can have a look at this article: https://support.pix4d.com/hc/en-us/articles/202557799-Menu-Process-Processing-Options-2-Point-Cloud-and-Mesh--Point-Cloud
The point density will differ as you change the scale of the image. The full-scale image will have more key points generated than the half scale.