Align chunks [T]

[CJ]

Hey folks,

I've been aligning chunks for a big project in PhotoScan Standard. The first few ones have worked well, but the last couple have thrown up a bit of an issue.

After aligning chunks (2) a [T] symbol appears at the end the chunk title. When merging these, the two chunks are off alignment in the merged DPC.

What does the [T] mean? And does it indicate a problem?
[R] = referenced, [S] = scaled
Have checked the manuals (Pro and Standard); and tried Googling it, but with no luck.

Cheers,
Cian

[Alexey Pasumansky]

Hello Cian,

Do the chunks appear properly positioned relatively to each other when "Show Aligned" option is turned on?

In the "Automation" section of PhotoScan Manual the [T] mark is described as:

T (Transformed) - Indicates that 3D model has been modified manually with at least one of the following instruments:
 Rotate object,  Move object or  Scale object.

But also it gives as indication for the aligned chunks that are not georeferenced with the coordinate information (via Reference pane in PhotoScan Pro).

[CJ]

Hi Alexey,

No, the chunks do not appear correctly aligned. They have the same amount of skew as the merged model.
Any idea what would be throwing these alignments off? The two models I am trying to align overlap with a high number of points and photos (it's an exterior facade which is aligning with an entrance - the entrance model maintains a section of the exterior).
The other chunks for the model have aligned perfectly (with one other exception).

When the [T] says that the model has been manually modified, does this imply that any attempt to align the model will be unsuccessful?
I have definitely modified the region, not so sure about the model. Will this affect alignment?

Out of curiosity, is there any way to un-align chunks? Haven't read anything about this.

Cheers,
Cian

[Alexey Pasumansky]

Hello Cian,

Then there doesn't seem to be a problem with the chunk merging - it merged the aligned chunks. So it's necessary to check why the alignment works incorrectly.

[T] in your case means that the chunks were aligned (PhotoScan has no indication, if they are aligned correctly or not, however, if the alignment fails, then this mark wouldn't appear on the not-aligned chunk). You can try to modify the position and orientation of the incorrectly aligned chunk using Rotate Object and Move Object instrument. It may be reasonable to do that in Show Aligned mode in order to see, how the model should be oriented.

Modification of the region (bounding box) doesn't have any effect on the chunk alignment operation.

[CJ]

Hey Alexey,

Thanks for those explanations.
Followed your advice on object manipulation and have got chunks close enough.

I ran "Merge Chunks" after that and it seemed to work fine. Should I have aligned the chunks again first?

Also, I have tried to delete some points using the lasso tool, however, they do not disappear. Not all points covered by the lasso tool are highlighted and the points that are seem to surrounded by a pink halo, as opposed to being entirely pink. I've edited merged chunks before, so I can't see why it's not working this time.

Cheers,
Cian

[Alexey Pasumansky]

Hello Cian,

If you run Align Chunks operation - it will discard any manual input for the chunks that are being aligned. So you can use Merge Chunks operation once you see that the relative orientation of the chunks is correct in Show Aligned mode.

As for the selection "issue" is it possible that you have enabled Show Aligned option and see all the chunks at once? In this case the selection instruments would be still applied to the active chunk (highlighted with the bold font in the Workspace pane).