Topics

1

General / Accuracy only in 0.001 m3 when I use DEM to calculate the volume?

« on: January 14, 2019, 11:32:21 AM »

Hi everyone,

I have a question.
I want to calculate the volume of a pit with DEM. V=V(after excavation)-V(before excavation). But I find if the value is bigger than 1 m3, the value could be accurate to only three decimal places (0.001), but if it is smaller than 1 m3, it could be accurate to six decimal places(0.000001). So I reset the "level" and get the value with accuracy in 0.000001 m3.
Could somebody tell me if my assumption is correct or not?

2

Camera Calibration / question about using the chessboard from the Agisoft lens software.

« on: August 23, 2018, 05:36:36 PM »

Hi,
I am new to calibration.
Now I have a question about using the chessboard from Agisoft lens.
I'm using Photoscan to make a 3D model for a object (such as a statue). And I want to use Agisoft lens for a percalibration.

I choose "Show Chessboard" and there is a big chessboard in the whole screen.
According to the manual I should take photos of the chessboard like the picture below.
But there is a problem. I use a prime Lens for taking photos. For the Photoscan process, all the parameters of camera should not be changed while taking photos. And I should use the same parameters to take photos of the chessboard. In this situation, the photos are badly out of focus because of the near distance between screen and camera.

My question is, can I play the focus to get the clear photo of chessboard? I'm using prime lens, I'm not sure it means the focal length also be fixed in this situation.

Can sombody help me?




The link of picture is:
https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=imgres&cd=&cad=rja&uact=8&ved=2ahUKEwi_78rKrYPdAhUKblAKHaeDBGQQjRx6BAgBEAU&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FThe-Chessboard-for-camera-calibration-in-laboratory-environment-Fig-5-The-sequence-of_fig3_322370374&psig=AOvVaw1ZvdPtEn4WbQLpQZnHUidQ&ust=1535119947141905

3

General / I have a question about camera calibration

« on: July 05, 2018, 04:30:42 PM »

Hello guys,

I'm a Uni student. Now i'm trying to do a project with Photoscan.

I know that there is a auto calibration of photos while making a 3D model. But sometimes it might work very well (such as not enough light), so i'm trying to do some manual camera calibration with other software (openCV or matlab).

I want to compare the result of manual calibration and  the auto calibration of photoscan and choose the right methode bevor i start my work.

But now i have a question: which kind of result (or which parameter) can i use, to compare the 2 way of caibration?

Can somebody help me?

Best Wish,

Jumboo