Compare two point clouds

Moustapha_Cisse · July 11, 2018, 10:13am

Hello Community,

Can pix4d compare two point clouds ?

I have two projects of same area at different times and i want to see the evolution.

I know i can use some third-party software to do it, but i just want to know if it’s possible in pix4d !

Regards !

Antigoni_Makri · July 16, 2018, 7:56am

Hello Moustapha,

You cannot directly compare two point clouds in Pix4D Desktop by comparing point by point their coordinates.

You can import a second point cloud in an existed project following the instructions of this article, but you will not be able to visualize both of them at the same time.

Regards,

Moustapha_Cisse · July 16, 2018, 8:24am

Helle Antigoni,

Thank you for your reply.

so, i will continue to use third-party software to do it.

Regards,

Pierangelo_Rothenbuhler · July 16, 2018, 8:57am

Hi Moustapha,

Could you elaborate on why you would like to have such a capability? What results are you looking to get?

If you describe your needs in more detail we better understand what we can do to help.

Thanks!

Moustapha_Cisse · July 16, 2018, 9:36am

Hi Pierangelo,

Thank you four your attention.

I work in quarries, and I need to compare point clouds for several reasons:

check that two surveys of the same site are correctly georeferenced with respect to each other,
identify areas that evolve between surveys for topographic plan updates (this allows us, for example, to do vectorization only on areas that evolve),
identify extraction areas for volume calculations (volume difference of 2 surveys ).

if I can have somethings like coloring one point cloud based on the distance to another one, it will be already helpful.

Regards,

Pierangelo_Rothenbuhler · July 16, 2018, 12:04pm

Thanks for the explanations. How often would you typically do this type of work for the same quarry? and what are the deliverables you need to provide at the end of the work?

Moustapha_Cisse · July 17, 2018, 7:18am

i have to do this type of work for the same quarry at each survey, and we have about 2 or 3 surveys each year.

The deliverables can be pdf report or image showing the distance by color between point clouds. I would take also screenshot of the raycloud, if it shows colored point cloud as in attached image below.

It will help if we can have volume difference (like in volume calculation ) between the two serveys by taking one of them as base surface.

Pierangelo_Rothenbuhler · July 17, 2018, 2:45pm

Ok, thanks for the illustration. Here is how I would summarize what you need when you compare two surveys of the same area:

show where change happened
measure the volume difference over the entire area

Let me know if I misunderstood. Thanks again!

Moustapha_Cisse · July 17, 2018, 3:11pm

Yes exactly, that is what i need, show where change happened is the main goal !

For volume difference, if i can have it only in one or some selected areas, it will be great! But if i can have it also over the entire site, it could be helpful !

Volume difference between two surveys like volume calculation is something usually needed in quarries, a fonction that can perform it will be very usefull.

Regards

Pierangelo_Rothenbuhler · July 18, 2018, 6:54am

Can you explain me why you need the volumes in selected areas and not over the entire site directly? How will these measurements be used afterwards?

Moustapha_Cisse · July 18, 2018, 7:52am

In quarries, over a given period, extraction are often done by phase on one or some well defined areas and not on the entire of the site. So we needn’t to use the entire of the site.
Customers therefore want to have the volume they have extracted only on these areas, so calculations must be done only on them

Measurements are used after to write a report where are indicated volumes extracted (volume difference between two point clouds, not volume of a stockpile) in defined period and some screenshot of these extracted areas.

Pierangelo_Rothenbuhler · July 18, 2018, 9:46am

Thanks Moustapha, I think I better understand the situation now. Will take it into account.

Moustapha_Cisse · July 18, 2018, 11:43am

Thanks you too Pierangelo, Let me know if you have some news about it. :)

Stephen_Kolenic · April 18, 2019, 10:44am

I have a similar problem, except that I have to do it monthly and I have to use 3rd party software to extract the data.

I also just want to overlay the two models and extract volume differences at selected areas.

Another problem that I would love to see fixed is:

Importing a base into the model and computing the volume between the base and the model.

I have large stockpile areas of which the base is known before and stock piling took place and it’s not always a smooth planar surface but has an irregular surface

Pix4D_Alumni_MV · April 24, 2019, 9:45am

Hi Stephen,

At the moment it is not possible to extract the volume difference as you are describing it.

However it is possible to import surface for volume calculation:

Best