What does "underscore symbol" mean in a matlab function documentation?

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Marco 2013-12-18

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评论： Soso 2015-4-2

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Hi,

I read in this documentation:

http://www.mathworks.it/it/help/vision/ref/estimategeometrictransform.html

that for output 'status'

[___,status] = estimateGeometricTransform(matchedPoints1,matchedPoints2,transformType)

but what does "___" mean?

I tried with

[~,status] = estimateGeometricTransform(matchedPoints1,matchedPoints2,transformType)

and

[tform,status] = estimateGeometricTransform(matchedPoints1,matchedPoints2,transformType)

but i can not get out status variable and it returns an error:

Error using coder.internal.errorIf (line 9)
MATCHED_POINTS1 and MATCHED_POINTS2 do not have enough points.
Error in estimateGeometricTransform>checkRuntimeStatus (line 167)
coder.internal.errorIf(status==statusCode.NotEnoughPts, ...
Error in estimateGeometricTransform (line 149)
    checkRuntimeStatus(statusCode, status);

回答（2 个）

Dima Lisin 2015-3-17

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Hi Marco,

If you look at the description of the transformType parameter in the documentation, you will see a table listing the minimum number of matched points required for each type of transformation.

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Soso 2015-4-2

Thank you so much Dima.

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Walter Roberson 2013-12-18

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The _ stands in for "any of the other forms listed already". So "tform" or the three-output form can both be followed by "status" as an output.

What size() are your matchedPoints1, matchedPoints2 ? The routine thinks that you are not passing in enough points (enough rows) to be able to compute the transform type you have asked for (you did not show us which one.)