If you are modeling 3D objects for just about any purpose, then one of the skills that you will need to learn is the ability to clean the topology of your model so that it behaves correctly when used with materials, lighting, animation, modifiers, and more. One tool that always comes in handy here is the merge by distance tool to remove duplicate geometry.
To remove your duplicate geometry from your model, Hit the TAB key to enter edit mode for your model, and then press A to select all of your geometry. Use the M hotkey to open the merge menu and then select the merge by distance option to remove doubles.
There are many reasons why you should be checking your geometry and ensuring that there are no incorrect normals, self-intersecting vertices, or duplicate geometry, and the merge tool is one of the quickest ways to clean up your topology of some of these issues.
How Do I Remove Duplicate Geometry In Blender?
The primary method for removing duplicate geometry in Blender used to be the remove doubles, which did exactly what it said, locating vertices that overlapped each other and then combining them into a single vertex.
That tool still exists in Blender today but is now under a different name. It is known as merge by distance and is one of several options under the merge menu.
To access the merge menu and use merge by distance, first hit the TAB key to enter edit mode for your object, and then select the geometry of your mesh by pressing the A key.
Go to the object menu located in the header bar of the 3D viewport and locate the merge option. Highlight it to open up the merge menu.
At the bottom of this list, you will have the By Distance tool, so select it to activate the merge by distance tool.
If you look to the footer bar at the bottom of your viewport straight after using the tool, you will see a small prompt that reads Removed – Vertice(s). The – hear indicates the number of vertices that have been removed.
If the geometry is literally overlapping, then you will be able to see in this prompt how many of these doubles were located and removed.
The operator panel for the tool will become available to you once you use it. Open the operator panel and you can adjust the distance threshold.
The higher the threshold value is, the greater the distance vertices can be joined from. Pushing this value too high will quickly begin to deform your mesh.
The unselected option underneath is used when you only have a portion of your model selected. When this is ticked the tool will allow you to merge with the nearest unselected vertices depending on the distance. Unticked the merge tool ignores your unselected geometry entirely.
Cleaning Up Geometry Where Vertices Are Overlapping
So in what situations do you need to focus on cleaning up your topology? Well, the number one thing you need to keep an eye out for is the occurrence of overlapping vertices, edges, and faces.
In addition to the merge by distance tool, there are many other tools that you can use to help clean up the geometry of your object, including the various other merge tools that will allow you to merge to specific points on your model.
For example, if we go to the merge menu, we will find several other options here. One option on this list is to merge to the first selected Vertex. This will allow you to merge all of your geometry to whichever vertex was selected first.
Alternatively, you can also merge to the last selected Vertex as well. The merge to cursor option will merge all of your selected vertices’ to the location of the 3D cursor.
On the other hand, the collapse option will collapse all of the vertices in on each other and will position the new vertex in the mean location, or the average location of all of the selected vertices.
What Happens If You Do Not Remove Overlapping Or Duplicated Geometry?
A key question to ask is exactly why do we need to do this in the first place? What is the main purpose of using the merge by distance tool or other tools to remove overlapping or duplicated geometry? One reason why this is important is to avoid shading artifacts.
When we use the smooth shading tool, we can make our objects look much smoother on the surface and make them appear more natural. However, if you have overlapping geometry and then choose to use smooth shading, then artifacts are likely to appear where your geometry is overlapping.
The reason why is because smooth shading uses the direction of the object and vertex normals to define that shading. And if you have overlapping vertices then their normals will be overlapping as well, which is what causes the shading artifacts.
Another reason why it is important to remove duplicate geometry and overlapping vertices is when you are using specific tools. There are a lot of tools in Blender that are influenced by the current topology of your object.
For example, if you were to use the subdivision surface tool on an object that has that overlapping geometry, then the subdivision surface tool or subdivision service modifier is going to try and divide up the geometry as best it can.
But as you have even more geometry in what is already a very tight space, shading artifacts are more likely to become visible. This is a result of the increased geometry in a very small space.
Another example is the Boolean modifier. The Boolean modifier allows you to take a Boolean object and cut a custom shape into your main object. However, if the Boolean overlaps any areas where you have duplicate geometry, then it’s going to create weird results that are not going to be useful to the user.
This can include the appearance of jagged edges for the Boolean as well as the inclusion of, again, shaded artifacts. Additionally, the failure to reduce the number of overlapping vertices and duplicated geometry will cause issues to your material application, your lighting effects, and your rigged animations.
In the case of materials, texture maps are required to layout the material on your object, and if the geometry is filled with this duplicate geometry and overlapping vertices, then that is going to impact how clean the texture will look on the model’s surface.
The shading artifacts that we have mentioned before will impact the way that the material reflects light, so those shading artifacts are going to change the way the light hits the surface of the object at those points.
When it comes to animations, if your object is a complex model, say a human character, and then you have duplicate vertices around the joint area, then the attempts to create different poses is going to create some unwanted behavior. This will make it more difficult to construct even basic animations.
Is There A Shortcut To Use For Bringing Up The Merge Options In The 3D Viewport?
As with most menus and tools, there is a shortcut that we can use to open the merge menu quicker, and that is to use the M on our keyboard. By pressing the M key we are able to open up the merge menu anywhere in our viewport. This allows us for a slightly faster workflow compared to just always going to the object menu and then locating the merge menu from that long list.
As for the individual tools found in the merge menu, they do not by default have their own hotkey assigned to them. One thing that we recommend is to assign the by-distance tool to your quick favorites.
To do this, hover over the by distance tool in the merge menu and right-click. Then select the add to quick favorites option from the context menu. You can access the quick favorites by pressing the Q key.
This may not seem any faster than using the M key, but if you don’t have any other options in the quick favorites then you can just press Q and select very quickly knowing that the by distance tool will be located in that menu.
Alternatively, you can add another hockey directly to the by distance tool. Again, hover over that all in the merge menu and then right-click to bring up the context options.
Instead of choosing the add to quick favorites option, select assign shortcut instead. One shortcut that is available to use in edit mode for mesh objects is Shift + M.
So hold down the shift key and then press the M key in order to assign this to your merge by distance tool. Now you should be able to access merge by distance just by using the Shift + M hotkey.
Using The Dissolve Functionality To Clean Up Your Geometry As An Alternative To Merging
In addition to the merged tools that we have available in edit mode, we also have the dissolve functionality that comes as another form of deleting our geometry.
While deleting your geometry will do exactly as it says and delete that geometry, dissolving will delete your selection and then merge the surrounding geometry so that the main shape is maintained. To do this, select the geometry that you wish to dissolve and then press the X key on your keyboard.
This will bring up your delete menu, but in addition to the delete options, you will also be able to see the dissolve options as well. We recommend using the dissolve vertices option to dissolve the selected vertices and merge them into your geometry to help clean things up.
Alternatively, you could also choose to delete an area of your model where you can see that there are overlapping vertices. By deleting that selection you can then select the surrounding geometry. Such as the edges of two faces, and then use tools like the face fill tool which is accessed by the F key to fill in the gaps in between.
By mastering the ability to tidy up the geometry of your object, you can make it more usable in many different scenarios, from 3D printing to animation to game design.
So make sure you learn the valuable tools of merging and dissolving your geometry in order to fix your topology.
Are There Any Modifiers That Can Remove Doubles And Unwanted Geometry?
As with many tools in Blender, not only do you have access to a tool that allows you to perform a specific function, but also a modifier that allows you to perform the same function procedurally.
There are two modifiers that will allow us to reduce the amount of geometry on our model. Although they are primarily for the use of reducing the geometry for the model as a whole.
This is different from just merging by distance where you are actually able to focus on any of the vertices that are really close together. The first of the two modifiers is the Decimate modifier.
The Decimate Modifier
With this modifier, we are able to reduce our geometry in one of three ways. The first method is a process called collapsing which reduces the amount of geometry on our model in a uniform way.
Then we have the unsubdivide option, which is useful for objects that have been subdivided and actually have good topology to begin with, which is not going to be useful if you have doubles.
And then we have the planar option which reduces the amount of geometry based on the angles of the edges that construct our model.
The Remesh Modifier
Alternatively, we have the Remesh modifier which is going to rebuild your model from scratch based on the resolution that you assign.
There are several methods with the remesh modifier but the best one in most cases is the voxel method. The remesh modifier is better suited when working with objects that already have very high poly counts such as sculpts.
For beginners, we do recommend using the decimate modifier in the case of if you are not going to use the merge by distance tool.
Thanks For Reading The Article
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