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jpascua
Posts: 197
Posted 22:32 Jan 18, 2015 |

• the formula for translate is : x'=x+tx, y'=y+ty, and z'=z+tz.
• the formula for reflection is:
◦ xy-plane is given by x'=x, y'=y, z=-z'.
◦ yz-plane is given by x'=-x, y'=y, z=z'.
◦ xz-plane is given by x'=x, y'=-y, z=z'.

So if the user selects a plane to reflect the points on, we plug in the prime formula given in translation? For example:

 

xy-plane is given by x'=x, y'=y, z=-(z+tz)

...

 

kknaur
Posts: 540
Posted 09:09 Jan 19, 2015 |

Translation and Reflection are separate operations and should not be combined into one formula. 

harry_520
Posts: 76
Posted 10:55 Jan 19, 2015 |

Shouldn't z and z' be reversed as z' = z and z' = -z?

jpascua
Posts: 197
Posted 11:55 Jan 19, 2015 |
harry_520 wrote:

Shouldn't z and z' be reversed as z' = z and z' = -z?

Yeah, that would make more sense to me... But the fact that it isn't reversed makes me think that the formulas are related.

kknaur
Posts: 540
Posted 14:01 Jan 19, 2015 |

Don't think of how to combine the formulas.  One function will apply the translate formula to all the points when the user chooses to translate and by how much, the other will apply the reflect formula when the user chooses to reflect about a specific plane.