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I made a geometry node where objects are placed on a curve at random distances.
I also used a realize instance at the end.
But the error "can't apply constructive modifiers on curve. Convert curve to mesh is order to apply" came up.
How can I fix it?
In Youtube tutorials on Geometry Nodes people when they start often say it does not matter which object you add to the scene, because they immediately get rid of it in Geometry Nodes and create something different.
This is actually not true if you want to apply the modifier afterwards. Curve objects have quite different settings in the Object Data Properties than Mesh objects. Meshes have a defined geometry of vertices while curves are procedural objects. You can for example change the resolution, change if you want them extruded or build a mesh with a profile curve - but this is all not fixed and can non-destructively be changed.
The Geometry Nodes modifier is a constructive modifier meaning it builds a mesh object. As long as you don't apply the modifier, all is still procedural and you can mix curves and meshes and change everything non-destructively. But as soon as you want to apply the modifier, the object "container" has to be a mesh, not a curve.
That's one reason why you cannot for example put a Displace modifier on a curve object. Even if you created a geometry on it, it cannot be displaced by the modifier because you have no real fixed geometry that could be displaced. The difference why you cannot put some modifiers directly on the curve object but do a lot in Geometry Nodes is, in the Modifier Properties it is clear you are doing this on a curve. Geometry Nodes is not determined to only create curves or meshes, they can be mixed as long as they are not applied.
So, to cut a long story short, if you have a curve object with a Geometry Nodes modifier and you want to apply it, you can do this by:
In both cases the object created by the Geometry Nodes modifier will be converted into a mesh object (or at least all objects that are a mesh or curve inside GN, volumes will disappear) and the modifier is applied afterwards.
Oh, another case where it is definitely not equal if you choose a mesh or curve object as base for your Geometry Nodes setup is if you want to have the possibility to draw curves in Edit Mode which are then converted to something else. Because you cannot draw curves on a mesh object in Edit Mode, in this case the base object has to be a curve.
