PC-DMIS

Tips & Tricks Dot vs cross

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Dot vs cross

JEFMAN over 5 years ago

I just write this thread because there still have questions about dot and cross products here, and I remeber that I wrote some other threads about them (links at the end).

Some reminders about differences between cross product and dot product.

The first one is important, the cross product creates a vector, the dot product creates a number !

Graphically, the dot can be represented like this :

The same way for the cross :

The problem about the cross product with PC-DMIS, is that the result is always a unit vector (the result is divided by its own length).
So you can't use it directly to calculate angles or distances.

A little more about it on those threads, old or not, giving explanations or examples...
https://www.pcdmisforum.com/forum/pc...xamples-of-use
https://www.pcdmisforum.com/forum/pc...sing-variables
https://www.pcdmisforum.com/forum/pc...of-dot-product
https://www.pcdmisforum.com/forum/pc...-about-vectors
https://www.pcdmisforum.com/forum/pc...on-from-points
https://www.pcdmisforum.com/forum/pc...point-to-plane

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JEFMAN over 4 years ago
There's a very old thread (or maybe it was a phone answer) in which I asked the question, the answer was "there's a cross_only function inside the soft, but it's not accessible to users", or something like this.
In the thread above, "cross_only" function should be "P_Vect" ("produit vectoriel" in french )

ASSIGN/V1=F5.XYZ-F4.XYZ ASSIGN/V2=F6.XYZ-F4.XYZ ASSIGN/P_VECT=CROSS(V1,V2)*SQRT(DOT(V1,V1))*SQRT(DOT(V2,V 2))*SIN(DEG2RAD(ANGLEBETWEEN(V1,V2)))

https://www.pcdmisforum.com/forum/pc...xamples-of-use
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JEFMAN over 4 years ago
There's a very old thread (or maybe it was a phone answer) in which I asked the question, the answer was "there's a cross_only function inside the soft, but it's not accessible to users", or something like this.
In the thread above, "cross_only" function should be "P_Vect" ("produit vectoriel" in french )

ASSIGN/V1=F5.XYZ-F4.XYZ ASSIGN/V2=F6.XYZ-F4.XYZ ASSIGN/P_VECT=CROSS(V1,V2)*SQRT(DOT(V1,V1))*SQRT(DOT(V2,V 2))*SIN(DEG2RAD(ANGLEBETWEEN(V1,V2)))

https://www.pcdmisforum.com/forum/pc...xamples-of-use
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mbatten over 4 years ago in reply to JEFMAN

Thank you! That should help. Do you know if computing it from the angle is better than using the XYZ coordinates? It's dumb we have to do this...

Interestingly, if you type out CROSS_ONLY in an expression, PC-DMIS takes it, but it returns zero. Weird...
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mbatten over 4 years ago in reply to JEFMAN

Also, do you know if this has been submitted as a bug?
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