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I have created an rdc file from google maps using RenderDoc, imported it into Blender (had to use version 2.83) and 'cleaned it up' by removing all unwanted vertices using the lasso select 'tool' with x-ray on as per videos on Youtube and very happy with the result. Watching another video tutorial the author used CtrlJ which joins everything into one mesh.

First of all apart from having one one mesh in the 'collection' what are the other advantages and are there any disadvantages? I will want to copy the object to another object when complete.

before ctrl J Before CtrlJ

after ctrl J After CtrlJ

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Well, it's a quite simple tool, the advantages and disadvantages are quite simple as well: it joins meshes. But you started your question with cleaning up meshes etc., Ctrl+J has nothing to do with cleaning up in a sense of making any geometry better or less messy. It's just that you have now one object in Object Mode where before were two or more. In Edit Mode the meshes are still separate parts.

The advantages are less objects in the Outliner and you can move, rotate, scale them all at once in Object Mode and all those before separate meshes stay together in relation to each other, no matter which Pivot Point you choose. In Edit Mode, if there are vertices close together you can merge them by distance to avoid doubled vertices. You can't merge two vertices even in the exact same location if the meshes belong to different objects. You can't create edges or faces between vertices if they are separate objects either. So joining meshes with Ctrl+J let's you do all those things. Of course other things like changing material is easier when it is all one object instead of multiple ones.

The disadvantages are for example, now that all those meshes are one object, you cannot simply have one with a Bevel Modifier and the other without or with different settings. To do that in one object you have to use methods like Bevel Weight or Vertex Groups to differentiate between which part of the mesh should be beveled and how much. But it's worse with the Subdivision Surface modifier, since this has no option to restrict the subdivision to certain vertex groups.

Applying materials is different, too. In separate objects, one can have e.g. a red material, the other a blue one. If they are one object, you have to assign faces to material slots to define which part of the object should have which color.

The good thing here is: if two objects already have different materials before joining, the Ctrl+J join will create a second slot for the second material and automatically assign it to the faces from the second object.

There are more examples to come up with, but as a general rule the advantages and disadvantages are simple, as I stated before: joing meshes into one object (apart from reducing the entries in the Outliner) let's you do many things in Object Mode that are sometimes difficult or may cause problems with multiple objects. In Edit Mode it is sometimes the only way to edit meshes together which would not be possible if they were separate objects.

On the other hand it's sometimes harder to do individual tasks on different meshes in one object which are maybe easy to do on separate objects. But altogether it depends a lot on how you are working and what kind of workflow you prefer. So I suspect this question will be closed due to asking for opinion-based answers instead of practical solutions.

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  • $\begingroup$ Thanks. Sorry for confusing you about 'cleaning up' Yes I know that has NOTHING to do with using Ctrl J and I only included that to describe everything I did. As the model is simply 3D photogammetry there would be little if no need to add a modifier but take on that information as it might be important for me later with other projects. Being able to rotate, scale etc shouldn't be a problem either especially selecting A(ll). Thanks again Gordon. $\endgroup$ Aug 4, 2021 at 8:52
  • $\begingroup$ My examples were not specifically for your model, the advantages / disadvantages of joining meshes are a general thing... Of course modifiers might not be of need here, but I thought my answer to be incomplete if I had just written "doesn't make much difference here" ;-) Although to clean up geometry it still helps if you can connect different parts in Edit Mode. Regarding scaling and rotating: what I said was the object meshes would stay in the same relations to each other, no matter which Pivot Point you choose. For example if you use Individual Origins on multiple objects... $\endgroup$ Aug 4, 2021 at 9:10

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