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Deleting Points in the Densified Point Cloud and Reprocessing

When I deleted points from the point cloud (select them and assign as deleted), I reprocessed just 3. DSM, Orthomosaic and Index, The DSM seemed to still have the data I deleted. For example, there were small trees I deleted to flatten the landscape, but when I reprocessed the data, it still generated a small tree in my DSM. Should I have reoptimized and then reprocessed the entire project or just reprocessed the Point Cloud and Mesh and the DSM and Ortho? I have not found any tutorials on the steps one needs to accomplish after editing the point cloud. All help is greatly appreciated.

P4DPro Ver:2077Nadar survey with phantom2v+
Dense Cloud editing / Point Group assignment

Issue:
Without deleting data but assigning points to groups then reprocessing with specific groups selected
in order to produce a mesh clear of non-terrian objects such as vegetation and structures. However
after reprocessing, all point groups are still represented in the mesh model as the are in the initial
processing point cloud.

Question:What is the procedure for producing mesh models by selecting groups and not deleting data important
for other mesh model needs?

Example:

Dense_Cloud


Dense_Cloud_Edited

Reprocessed_Mesh

@Mark: The procedure that you describe is correct. In step 3, the DSM will be generated from all points of the point cloud that are not in the Delete group. So if you assign some points to the Delete group they should not appear in the DSM.

Note that if there are some “holes” in the point cloud due to the editing, the DSM will be interpolated to fill these holes. So if you delete only a small portion of the point cloud if might be difficult to see that it is missing in the DSM.

Have you observed the same behavior by deleting points of a larger area?

Note that if you want to flatten the DSM you can draw a surface in the rayCloud. If you draw a surface, the DSM will be projected on this surface after step 3. Note that you need to make sure to use the surface for the generation of the DSM:

Note that if you process again step 2 the point cloud will be overwritten and you will have to edit the point cloud again.

@ Gary: Similarly to the DSM, the 3D Mesh will be generated from all points of the point cloud that are not in the Delete group. To generate the mesh only from the terrain. You should put the objects in the Delete group and then generate the mesh: Process > Generate 3D Textured Mesh.

It is a good suggestion to be able to select the point group from which you want to generate the 3D mesh. We have passed your suggestion to our product management team.

Regards,

@ Gary:  Thank you for the tip on assigning points in the cloud.  I had been just assigning everything to the deleted file in an attempt to flatten the DSM and it has been very labor and time intensive.

@ Pix4D Support:  Thank you.  I am trying to flatten the DSM to prevent artifacts and crowning over trees.  I am flying forestry for analysis and the customer’s analytical software works best with an orthomosaic that is rendered from a flattened DSM.  So if I understand you correctly; I need to create the surface in the point cloud, check “Use for DSM” and process Step 3 again (not Step 2).  This will flatten the DSM and the ortho should be rendered from that?  

If you have any other tips on flying dense forest it is greatly appreciated.  I didn’t realize that getting good results over trees at the altitude restrictions set forth in the States would be so difficult.

Thank you,

Mark

Hello Mark,

The orthomosaic derives from the DSM. Pix4Dmapper 2.0 is using the Inverse Distance Weighting (IDW) algorithm for the DSM generation by default. This algorithm wasn’t implemented in 1.4 that used the Triangulation method.

The IDW algorithm is more adequate for buildings rather than trees. This is why we suggest that you switch to the Triangulation method. For Pix4Dmapper 2.0 you can change the processing options for step 3 (raster DSM) following this link:
https://support.pix4d.com/hc/en-us/articles/202557769#label5

Regarding the processing to flatten the DSM and obtain the corresponding orthomosaic, you should indeed draw the surface, check the ‘‘Use for DSM’’ option, and run step 3 only.

Best regards,

I’m facing exactly the same issue as Mark:

“When I deleted points from the point cloud (select them and assign as deleted), I reprocessed just 3. DSM, Orthomosaic and Index, The DSM seemed to still have the data I deleted. For example, there were small trees I deleted to flatten the landscape, but when I reprocessed the data, it still generated a small tree in my DSM.” 

I know I can use surfaces to flatten the DSM, and, when it is created the DSM, it is flattened, but just on the surface area. Eventhough, the model is quite big, full of holes (PIC 01 - buildings, vegetation, automobiles, etc…), so it is not viable to create surfaces to cover all them. There are point just on “Terrain”, all the rest is “Deleted”.

It is the second time it´s happening since the last update (current version is 2.1.49). Any idea of what could it be? looks like a software bug.

 

PIC 01: just a part of the model

PIC 02: the countours of approximately the same part of the model with elevations where it should be flat.

PIC 03: area covered with surface and holes

PIC 04: contours before and after (blue and red) covering the area with a surface. The elevations around it are not fixed - should be interpolated and, therefore, be approximately flat. 

Thanks,

Wagner Gasparotto.

Hi there,

bug is still not fixed on 2.1.52.

 

Corresponding DSM of the same region:

Thanks,

Wagner Gasparotto

We have the same issue.  2.1.52 still has this bug.  Can anyone point us to an earlier version that works?

Hi all,

This should be fixed in 2.1.58.
Let us know if you still encounter problems.

Regards,

I also noticed they you cant delete the Automatic points in the ray cloud?  And this prevents the trees I try to delete popping back again?

Hi John,

It is true that you can not delete automatic tie points (only densified points). I have added your idea to our Suggestion list.

Please keep in mind that with the new version 3.1 that can be downloaded here https://mapper.pix4d.com/download/

you can generate a DTM (Digital Terrain Model) without the trees with an automatic workflow.

Have a nice day,

Christina

 

That’s what I am now using Christiana. I had tried the automatic DTM in the earlier versions but it would also delete parts of the hills. I’ll try it again. Thanks.

 

Has there been an answer to this?  I am trying to do something similar.  I have edited the point cloud to regenerate a better triangle mesh.  I have assigned points to different groups.  I would like to be able to create a mesh from each of those groups, or to create a mesh only from the layers that I have checked (visible). I would also like to generate different mesh qualities (high, med, low, custom) for different applications.  

It seems that the only way to even generate the mesh that I want is to move all of the other points into the deleted group… which then removes them from the individual layers I spent so much time assigning points to.

I then tried to export each of the layers as an individual point cloud to try and import them into a new project in order to generate the mesh.  No luck.  It generates a mesh, but it’s messy and untextured.  

It seems like this should be easier to do.  For reference, I am needing the individual components to create models of buildings / equipment that I can import into exploitation software to represent how a site will look - during the operation phase of the project - while still in the planning phase of a project.  

Any help would be greatly appreciated.

I feel your pain!
However, now software stability is the big problem for me.

Happy new year everyone :slight_smile:

@Chris: Currently, there is no way to generate a Mesh based on a specific point group. You would need to put all points, that you are not interested in, in the group “Deleted” and then generate your Mesh: https://support.pix4d.com/hc/en-us/articles/202557899

Pix4Dmapper will not take into account the points that belong to the group “Deleted”.

(this is what you have already tried! I understand that it is a pain and you lose the assignment that you have already done…)

 

Your idea (generating a Mesh based on a specific point group) is very good and I have added it to our Suggestion List. Our Product Development Team will consider it for the future version of the software.

 

Have a nice day,

Christina

 

What about the macOS version? I’m running 3.0.13 and I’m pretty sure my DSMs all include points from the Deleted group. Is there a way around this?

Hello Darren, 

Are you still facing the same issue?
Which version do you have installed? 
Can you describe the procedure you followed?

Did you assign the points to the Deleted point group and then processed Step 3? 

 

Best Regards, 

Hi there

I am having the same issue on the Mac version (3.0.18): points within the “Deleted” point group are being considered for generating the dsm and orthomosaic.

@ Pix4D Support: Will there be a fix to this bug anytime soon? Or is there a workaround?

Best regards,

Clemens

Original pointcloud:

Orthophoto from original pointcloud:

Edited pointcloud:

Orthophoto from edited point cloud:

Hi Clemens, 

The DSM should not take into consideration the deleted points. Just edit the point cloud, save the project and regenerate step 3. 

The orthomosaic, will be generated based on this new DSM but takes the color from the input images. In your example, the pink roof that was deleted cannot be replaced by “ground color” points in the orthomosaic, as the input images do not contain such information.

If you are interested in correcting the orthomosaic, the Mosaic Editor could be a good tool for you: 

https://support.pix4d.com/hc/en-us/articles/202560079

check here some good examples of using the Mosaic Editor: https://support.pix4d.com/hc/en-us/articles/202559959

https://support.pix4d.com/hc/en-us/articles/202559939

You could also use it to remove moving objects such as cars.

For more information: https://www.youtube.com/watch?v=KUYSy1cIy7s

I hope my answer helps you with your projects :slight_smile:

Christina

 

Hi,

 

I have the same issue :

  • edited dense cloud and deleted some points for a part1 classified in deleted group for a secont part.

  • save project (if i re-edit the dense cloud points are no more there)

  • run step 3 only

  • still get the deleted road (in fact in truncated dense cloud with a big part of it as a test).

  • furthermore question is how to delete impact of electric wires above a field ?

I cannot find any points in the cloud that correspond to this electric line.

Regards

NB i have Ag version , is this a problem to do so ?