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https://issues.apache.org/jira/browse/GEOMETRY-119?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17312511#comment-17312511
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Gilles Sadowski commented on GEOMETRY-119:
------------------------------------------
{quote}types of situations occur frequently outside of the library
{quote}
I'd propose to overload {{normalize}}:
{code:java}
public Vector3D.Unit normalize(boolean abort) {
final double norm = ...
if (norm == 0d) {
if (abort) {
throw new ...
} else {
return null;
}
} else {
return normalizedVector;
}
}
public Vector3D.Unit normalize() {
return normalize(true);
}
{code}
User code would still explicitly check for {{null}} and act accordingly.
{{normalizeOrDefault}} would then be syntactic sugar which IMHO does not belong
in the library.
{code:java}
public Vector3D.Unit normalizeOrDefault(Vector3D v, Vector3D ifNull) {
final Vector3D.Unit n = v.normalize(false);
return n == null ?
ifNull :
n;
}
{code}
> 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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