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https://issues.apache.org/jira/browse/GEOMETRY-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17312442#comment-17312442
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Matt Juntunen commented on GEOMETRY-119:
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> It seems that mentioned use-cases can use the "internal" functionality of
> {{tryNormalize}}.
My point is that these types of situations occur frequently outside of the
library, where {{tryNormalize}} is not available. For example, in my day job we
have code that processes user input in the form of triangle vertices. As part
of this, we need to compute the triangle plane normal. However, some triangles
are degenerate, meaning that the points do not define a unique plane and the
computed normal is zero. We currently have to check for this case before
attempting to get the normal since otherwise an exception will be thrown. It
would be great if we could use {{normalizeOrDefault}} to check and normalize in
one step.
This is just one example. In general, this method would be useful anytime you
need to normalize something that came from user input.
> Vector normalizeOrDefault() method
> ----------------------------------
>
> Key: GEOMETRY-119
> URL: https://issues.apache.org/jira/browse/GEOMETRY-119
> Project: Apache Commons Geometry
> Issue Type: Improvement
> Reporter: Matt Juntunen
> Priority: Major
>
> A frequent use case when working with vectors, especially vectors coming from
> external data, is attempting to normalize the vector, and if this is not
> possible, to use an alternative value. For example, the
> {{QuaternionRotation}} code
> [here|https://github.com/apache/commons-geometry/blob/master/commons-geometry-euclidean/src/main/java/org/apache/commons/geometry/euclidean/threed/rotation/QuaternionRotation.java#L86]
> does exactly this; it attempts to normalize a vector and failing that (ie,
> if the vector is exactly zero), it returns a substitute value. The
> {{QuaternionRotation}} class is able to take advantage of our internal
> {{Vectors.tryNormalize()}} but callers outside of the library are not able to
> do so and so are left with 2 choices:
> 1. wrap the {{normalize()}} call in a try-catch and handle the exception
> thrown on illegal norm values, or
> 2. compute and test the norm prior to calling {{normalize()}} to ensure that
> the call won't fail, resulting in 2 computations of the norm.
> Neither of these options are very good.
> I propose adding a new method to the Euclidean Vector classes to handle this
> situation: {{normalizeOrDefault()}}. The method would accept a default value
> (possibly null) to return if the vector cannot be normalized. The normal
> would then only need to be computed once and an exception would not need to
> be thrown in case of failure. The behavior of the current {{normalize}}
> method would be the same.
> Examples:
> {code:java}
> // get some kind of normal, preferably vec but +z will also do
> Vector3D.Unit norm = vec.normalizeOrDefault(Vector3D.Unit.PLUS_Z);
> {code}
> {code:java}
> // throw a very use-case specific error message
> Vector3D norm = vec.normalizeOrDefault(null);
> if (norm == null) {
> throw new Exception("Invalid triangle at index " + i + ": cannot compute
> normal.");
> }
> {code}
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