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I have two homogeneous coordinates and I am trying to preserve the distance between two coordinates after various affine trasnformations. Should I calculate the angle between two points ? If so what is the formula to calculate the angle between two points or is there a distance formula other than the general euclidean plane? I found that euclidean distance formula will not preserve the distances

what is the distance formula between two homogeneous coordinates

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    There's no such thing as distance in the projective plane -- it becomes projective partly from _ignoring_ the concept of distance. – 2017-01-23
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    @HenningMakholm So should I calculate the angle between the coordinates ? – 2017-01-23
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    That depends entirely on what you want to achieve. (Note that this angle, if I understand correctly what you mean, is not a projective invariant). – 2017-01-23
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    @HenningMakholm Assume I have a camera and I am moving towards the camera and away from the camera – 2017-01-23
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    What do you mean by “I am trying to preserve the distance […] after various affine transformations”? Is it that you have the affine trafos and want to *show* that they preserve distance? Or *check* whether they do preserve distance? Or is it that you want to append one more transformation in order to *make* distances as they were? If so, what kind of transformation? Or is it that you want to *tune* some parameters to ensure that distances are preserved? Do you want to preserve orientation as well, or may orientation be reversed? – 2017-01-24
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    @MvG I am trying to get back the original distance formula after same affine transformation performed on the homogeneous coordinates. Take the example of scaling after performing scaling on coordinates I want to apply distance formula and get back the original distance formula. – 2017-01-24

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