# In 3D free point on xoy

Rumburak shared this question 6 years ago

What command can define a point free in xOy which can not move on z-axis ?

You can use A=PointIn[x>=0&&y>=0]

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For new points you can click with the point tool on the x-axis or define it with the command Point[xAxis]

But if the point is already there then you need to go to the definition in the property view and change the defintion to Point[xAxis]. Or just redefine it.

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Thanks, but I know that. I am interested only in xOy plane and NOT on z-axis. Without an duplicate plane of xoy.

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I don' t what you want ... pleade explain it more exactly.

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hi

when you create a plane a as z=0 and the a point A=Point[a], you've got a free point in the xOy-plane which you cannot move vertically.

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Point[xAxis] move only on x-azis. Not on xOy plane .

I created a plane identical with plane xOy (a) and I positioned to him my point (PointIn [a]).

I think there is a command to put point directly on xOy plane ...

Please tell me what do you not understand

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hi

A=Point[z=0] will do directly without creating a plane first.

chris

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Yes this is it. Thank you very much

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z=0 este ecuatia planului [XOY}

dumneata vrei sa muti punctul pe verticala ?

din ce am vazut eu, in fereastra 3D, punctele se creaza in planul z=0 si dand cllck pe ele, in jurul lui apar sageti de sens pentru miscare in plan, iar daca se mai da click o data apar sageti de sens pe axa Z. :-)

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Am dorit ca punctul sa fie creat direct in planul xOy si sa nu poata fi mutat pe verticala . Adica in primul rand sa fie mutat numai in z=0 si apoi numai pentru valori pozitive pentru x si y.

In plus am intrebat daca exista o comanda directa pentru astea si se pare ca nu.

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ce apartine planului [X0Y] se vede si in fereastra 3D. adica desenand in 2D, se vede si in 3D. daca nu doriti variabila pe Z, atunci nu este mai simplu ca sa lucrati in [X0Y]

aceasta nu pare a fi intrebare de matematica, este intrebare de utilizare a editorului. am deschis un topic despre ce este GeoGebra si cum poate fi folosit el: Sa utilizam Geogebra

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Ah ... I did not understand it correctly what you mean.

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This point can have positive coordinates ?

ex: Point A = [z = 0, x> 0, y> 0]

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You can use A=PointIn[x>=0&&y>=0]

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Yes, that is what I wanted.

Maybe it will work for z ( PointIn[(y ≥ 0) ∧ (z ≥ 0)] not wotk )

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this sintax is not possible.

you can do an "on update" script similar to this post

https://www.geogebra.org/he...

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I understand. Thank you

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hi

but you can create something that looks like it. When you create veelhoek1=Polygon[(0,0), (50,0), (50,50),(0,50)] then PointIn[veelhoek1] will have positive x and y and z=0. (If you want to avoid 0, you can use (50,0.1) ore something like that).

Sometimes we have to content ourselfs with the result of a trick instead of simple beauty...

chris

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This is the simplest solution. Thank you ccambre and mathmagic for good answers

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I found a syntax out of help. I hope it is not a bug.

I tried dynamics coords in 3D for B=(x,y,z) 0<x ; 0<y ; 0<z

this is the work

move B in three directions

it is easy another conditions for B

Files: foro.ggb
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I used for point B :

DynamicCoordinates[A, If[x(A) < 0, 0, x(A)], If[y(A) < 0, 0, y(A)], If[z(A) ≤ 0, 0, 0]]

Excelent solution mathmagic :)

However, when you click twice can be confusing due to displacement point A to z> 0

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DynamicCoordinates[A, If[x(A) < 0, 0, x(A)], If[y(A) < 0, 0, y(A)], 0] is better

the A point must be hidden

the 3D dynamic coords are in process