Chapter 9: Combining two clouds into one

So creating a simple 3D model is not enough for you? By all means, we can do more. For example, we could try to create a full 3D model without the table or whatever the object is placed upon. But how do we do that? First, you need to know that you only really can do that with the Professional Edition of Metashape. Rudimentary alignment of two Chunks is possible with the Standard version, but it is not very good. It is more or less simple and here I will explain how to do it. You should start out with a normal 3D model of your object, like you did before. So have a look at this base of a bi-face on the left. It looks like the objects we have done before. Now, if you remember, as a first step, you had to load the photos into the software in something that is called a Chunk. The amount of photos was written as cameras besides it, see screenshot on the side. My example has 105 photos, that were taken from the base of the object.

Now let's create another Chunk by clicking the Create a new Chunk-button above the left window. You should have now a Chunk 2 in your list and by double-clicking, you can make it the active chunk. Now, you proceed as before: Add Photos, Align Photos, Build Dense Point Cloud and Build Mesh. But of course, you will not take the same photos as before, rather then new photos from the other side of the object. So in my case, that would be the tip of the bi-face.

What I like to do next, is to make a copy of these two chunks first, because I want to delete a couple of points and it makes sense to me to keep a copy of the whole data-set, in case something goes wrong. You can create a copy by right-clicking the active chunk and choosing Duplicate.... You should create a copy of each chunk, so that now you have four chunks, two from the base and two from the tip. Then we have to have a close look. We want to see which parts of our object are the same in both chunks, because the data overlaps and we need that. I like to work in the Dense Point Cloud for this.

By double-clicking our first chunk copy (the base) we can make it active and change to the Dense Point Cloud-view, if you not already have. What I want to do is to have a clear view of the lower part of my object, so I can select and delete all the other points, that I do not need. When done, it should look something like this screenshot on the side. You see the clear cut I made? There is still plenty of overlapping to the other chunk, but I got rid of all the unnecessary bits. Now let's turn to our second copy, the tip of the object.

Here, we do the same. First, let's navigate to get a good view and then we delete all the points we don't need. The good thing is, that we work with copies of the chunks. So if something does not work out, we can start over, because we still have the original chunks. If you have also prepared the second chunk, we can try a first rudimentary alignment. If you click on Workflow/Align Chunks... you can choose the chunks to align. Leave the original ones alone and just select your copies. You can also hit the Adjust Scales-checkbox and hit OK. Let's see what Metashape has done.

Sometimes this alignment works. Metashape is trying to figure out how these two chunks fit together. It searches for identifiers that match in both point clouds. Most of the time however, it will not work out at all. Don't worry, that what markers are for. If you search for some interesting points on the objects yourself, you probably find some spots or cracks or whatever that are visible in both chunks. Have a look at the example to the side. In the red circles, the same spot is marked, seen in both chunks.

Now, by right-clicking on certain spots of that feature, we can add so-called Markers. Find a spot that you see in both chunks and give it the same marker (so the same marker number). In my case I gave the upper part of that spot the marker 4 and came around a bit later to give the lower part of that spot the marker 12. If you can't see the marker (or want to turn them off later), you can use the little flag symbol on the top tools row. Just make sure, that marker numbers correspond in both chunks. So always go back and forth. Try to find as many markers as you can. Sometimes that is easy, sometimes that is hard. 12-20 points are plenty. So, now we can do the alignment way better. By again clicking Workflow/Align Chunks... we can restart the process. This time, we make sure the method is set to Marker based. When the process is done, you don't see so much at first, but if you switch now between the two chunks, you should see, that they have aligned and are positioned relative to another. Great!

Still, we do want to have one single chunk, so we can produce one single 3D object. For this, we select Workflow/Merge Chunks.... Here, we select the two chunks that we aligned just now and make sure that Merge dense clouds is selected as well as Merge markers. When we hit OK, Metashape will create another chunk, this time combined. We now have a dense point cloud of the whole object. We now only need to redo the meshing and texturing part, but you already now how this goes. Happy meshing!

This page was last edited on 2024-04-11 14:21

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This page was last edited on 2024-04-11 14:21

Sebastian Hageneuer
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