Median of the catenary below normal

[joan.cano]

Hi everyone,

I was using Pix4D Survey and I’m really excited with this new software, good job!

However, I was traying catenary tool with an own dataset which we capture with eBeeX. Catenary lines were drawn with a stereo software, and x,y,z of the catenary were checked with a Laser scanner. Results were good at all axis.

When I draw the catenary with P4D Survey start lines are perfect but the median of the catenary is usually below normal.

Do you know why it can happen or do you have a procedure that has not yet been published? That would help me a lot.

This is the procedure that I have performed

[Blaz]

Hi Joan,

Great to see you are trying out Pix4Dsurvey

I think that the reason why the line, in the case you shared, does not fit the actual position is that the points were not defined precisely enough.

The point on the power line should be marked on the exact same spot on the images. I would recommend using characteristic points that are easily identifiable in images, for example, where the line is attached to the tower. Although, finding a characteristic point in the middle of the line can be more challenging.

It is easier to digitize catenaries is they are reconstructed in the densified point cloud. In order to achieve this, we recommend increasing the overlap and decrease the GSD while flying the mission.

You could also try changing the processing options in Pix4Dmapper to extract more points in the project. For example, run Step 2 again after setting the value for Minimum Number of Matches to 2.

You mentioned that you have laser scanner data available, did you try importing the laser scanner point cloud into Pix4Dsurvey and use it for vectorization?

Best,

[joan.cano]

Hi again Blaz,

I followed your advices and the results are great. Even I checked with the point cloud from laser scanner and match.

“Find a characteristic point in the middle of the line can be more challenging”, I’m agree.

When I try to import only the laser scanner point cloud, is not able to find the coordinate system. But if I import it after importing the projet from Mapper, I can import but still saying coordinate system unknown.

Best,
Joan

[Blaz]

Great news! I am glad it worked well.

If the coordinate system is not directly written in the header of the .las file, then the warning you get is expected. Importing of a .las /.laz file without the coordinate system definition:

• Is not possible in an empty project.
• Is possible in an existing project. Note that the coordinate values of the imported point cloud need to match the ones in the existing project in order for it to align.

More in the Project management - Import point clouds article.