The Ultimate Houdini node reference
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The Convert SOP will allow you to convert one primitive type to another.
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Use the convert sop when you want to go from one type of primitive to another. Not all conversions are directly possible, but remember that you can always convert to one type of primitive and then convert to another. If you're not familiar with the basics between different primitive types, the Node Bible's Box SOP has a great explanation which compares NURBS vs. Polygons vs. Bezier, etc... This may provide you with a basic understanding of various primitive types to get you up and running with the terminology. Keep in mind that this node is not ideal for converting volumes. If you're trying to do that, then use the Volume Convert or Convert VDB nodes instead.
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-- Allows you to isolate the resample to a certain group of points/primitives. Read up on the Group SOP node bible entry if you're not familiar with groups yet.
-- What sort of primitive are you converting from?
-- What sort of primitive are you converting to?
-- When converting from one primitive type to another, how would you like the typology drawn out? For example, if you are converting a NURBs surface to polygons, you can specify that you would like those polygons to be all quad typology (meaning that each face has four sides) by selecting “Quadrilaterals.” Any time you’d like to adjust the resulting topology, try experimenting with these settings.
Level of Detail:
-- The documentation fails to thoroughly describe the differences between “Level of Detail” and “Divisions Per Span,” so this is my interpretation between the two parameters:
-- The Level of Detail and Divisions per span are similar in that they define the density of topology in the resulting primitive. If you’re not sure which one to use - then just go with whichever one looks better for your situation. They’re both very similar, so in most situations it may not practically matter.
-- Level of detail figures out how many polygons, spans, etc. by looking at how large the elements are in what’s called “Voxel” space. Now, be careful here because the term “voxel” is poorly used here. In this situation, “Voxel” does not refer to a volume. It refers to the relative distance between two spans. Also notice how Level of Detail uses a float value to determine the detail. This may become important when creating LODs for a given object that needs to be arbitrary based on the distance between the object and a camera.
-- Divisions per span is different because it specifies an exact number of divisions between each span.
-- In conclusion, the main practical difference between the two parameters here is that one uses arbitrary float data and the other uses integer data for determining the density of the converted geo. This may become relevant when setting up the LOD (level of detail) on objects, but in most situations outside of that, these two settings will provide you with about the same effect.
U & V:
-- Instead of dividing things in the X and Y direction, U and V are used. U and V are used instead of X and Y because their direction is relative to the direction of the incoming topology. For practical purposes, it’s best to just adjust them and see what they do to the object.
-- The Trim-Curve is useful for whenever you’re converting a Trimmed NURBS Surface, Bezier Surface, or Bezier into polygons. If you’re faced with that situation, then this parameter will increase/decrease the point density along the edges of the original curve.
U & V Order:
-- This is only available when using Bezier or NURBs. Imagine a certain number of cvs (control vertices) which span across each surface patch. The number of cvs which belong to each patch are determined here. To see what this does, simply play around with the parameters and move the resulting cvs around.
Paste Coordinates & Attributes:
-- According to the docs, “Evaluate base or feature surface for position.” This, however, does not really explain anything about what this does unfortunately. In practice, the defaults have always worked for me, and I would generally ignore this parameter. If you happen to know more about these parameters, feel free to contact me and I’ll be happy to update this section.
-- Preserves the original typology of the object
Interpolate through Hulls:
-- If you check this on, then the level of detail and divisions per span will become unavailable to you. Again, the documentation doesn’t have a great explanation for what this does in practice. It says, “Splines will preserve the shape of the geometry they are converted from. Otherwise, points in the geometry are used as points in the hull.” In practice, I never use this and it's practical use is unclear at first glance.
-- If you’re converting to a volume, then this determines where polygons are drawn based on the voxel value specified here. If you are trying to convert a volume, do not use the Convert SOP. Instead, use Convert Volume or Convert VDB.
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