Find the accuracy of a camera

[Ferdian87]

Hi everyone,

Recently I use a smartphone camera for digitizing an accessory wooden box. After placing six GCP, I use the control distance between GCP 1-2, 3-4, and 5-6 (images 1). On the real object, I found the real distances are 14 cm, 9,25 cm, and 2,4 cm. After scaling the model with the real distances, and I found the final residual values are 0, 0518; 0,0696; and 0,0269(images 2). Now the questions.

1. I found on some website says that to get the accuracy, I just need to sum the residual value and divide it by the number of the data(in this case 3) which they called it RMSE. And I found the value around 0,0494 cm. Is this the accuracy of the model? Did I do it right?

2. On some paper, I found people mention X, Y, and Z accuracy, what that's mean? Is that also related to pixel accuracy? Where I can found the information on 3DF?

3. I believe the size of the object and the distance of the camera affects the accuracy of the model. Is there a way to know the maximum size and distance to get the optimum accuracy of a camera for photogrammetry?

Thank you in advance.

[cam3d]

Hi Ferdian87

Here's the 3DF calculator to help determine theoretical accuracy https://www.3dflow.net/technology/do...sion-accuracy/

Accuracy is a bit of a tricky subject to quantify - You also need to account for any human inaccuracy when selecting control points

- For practical purposes, when I am checking accuracy for myself, I determine a few known points on my subject, scale the model with a pair of control points, then cross-reference this pair with other pairs to ensure the model is accurate within my required specifications (usually 0.5mm for short-range scans).

[Ferdian87]

Thank you for the answer @cam3d

I found another article for Ground pixel size, unfortunately, I don't know the sensor size of my smartphone camera.
For practical purposes, can we compare the 3Dmodel to the real object to know the accuracy (Like what I did)?

[cam3d]

Ferdian87 You can measure points on the real object and cross reference them with the 3D representation from Zephyr OR if you have a perfect digital model of your subject in you can use the point cloud comparison tool (more on this tool here: https://www.3dflow.net/zephyr-doc/en...istration.html) to compare your scan data with a ground truth.