datum plane creation is unintuitive

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uwestoehr
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datum plane creation is unintuitive

Post by uwestoehr »

My task is to create a datum plane 5 mm above the x-z plane. Therefore I
- create the datum plane
- then I want to select the x-z-plane but I cannot

How can I make the planes appear so that I can select them?

- since I could not select it, set it manually by entering "XZ_Plane" in to the first field.

OK, now I have the plane I want but because I want it 5 mm above the plane, I want to set the offset for y to 5mm. But all offsets are disabled.

- Therefore I change the attachment mode from "Plane face" to something else and them back to "Plane face"

Now I can specify offsets.

- I change y to 5mm, but the plane is not moving
- OK, I try the z-offset, and then the plane moved along the y-axis

So changing z-offset results in the desired y-offset.

So all in all either I do something completely wrong or there is a bug. Or maybe I just have a thinko about the datum planes?
freedman
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Re: datum plane creation is unintuitive

Post by freedman »

For this kind of post you should follow the pink bar above.

In the tree you can use the "Origins" to select any standard plane.
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meme2704
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Re: datum plane creation is unintuitive

Post by meme2704 »

Hi
Nothing more simple, When you select "New sketch", you have a small window that appears to choose in which plane (XY, XZ, or YZ) you also "Offset": if you type 5 the new plan will be 5mm at above the origin
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GeneFC
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Re: datum plane creation is unintuitive

Post by GeneFC »

uwestoehr wrote: Wed Feb 13, 2019 4:09 pm So changing z-offset results in the desired y-offset.
This is a somewhat strange behavior when you are not accustomed to it. The movement you want is in the z-direction of the local coordinate system for the plane.

I believe this is a "feature", not a "bug", but I do not fully understand why.

Gene
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Re: datum plane creation is unintuitive

Post by chrisb »

If you encounter problems with selecting, make everything invisible except the thing you want to select.

The Z-direction is always perpendicular to the plane. DeepSOIC has explained it somewhere here and it's reasonable, because you rather want an offset from the plane then from something outside of the coordiante system given by the plane.
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uwestoehr
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Re: datum plane creation is unintuitive

Post by uwestoehr »

meme2704 wrote: Wed Feb 13, 2019 4:26 pm Nothing more simple, When you select "New sketch"..
It is not that simple because
- I don't want to create a sketch
- the datum plane also needs an angle
chrisb wrote: Wed Feb 13, 2019 5:08 pm The Z-direction is always perpendicular to the plane.
I see but I find it very unintuitive. Because when I need a new coordinate just for the datum plane, I can set up a datum coordinate system.
freedman wrote: Wed Feb 13, 2019 4:16 pm In the tree you can use the "Origins" to select any standard plane.
But why not directly using the task dialog and clicking into the design. I mean when e.g. adding a cylinder or similar the 3 origin planes are automatically made visible to select. Only for the datum plane dialog they are not. That is why I gave this thread the name "unintuitive".
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Re: datum plane creation is unintuitive

Post by NormandC »

If you have useful insight, not only criticism, please reply over there and get to work: https://forum.freecadweb.org/viewtopic.php?f=34&t=20071
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Re: datum plane creation is unintuitive

Post by wmayer »

When you create a datum plane then you must already have created a body beforehand. The body has an origin which is hidden by default. So, the easiest is to first show the origin and then select its xz plane. Now when creating the datum plane it is already correctly aligned.

In the offset dialog you will see the three axes X, Y and Z. They represent the local coordinate system of an object and not the world coordinate system. Having them in world coordinates doesn't make sense anyway because whenever you change the orientation of the object the datum plane is attached to you would have to change these values.

The tool tip of the X, Y, Z labels mention that it's in local coordinates but it might be good to have a label at the top of the group box that is always visible and clearly states how to interpret the axes.

One could also use letters like U, V and W but this doesn't really solve the confusion because in the property editor again the letters X, Y and Z are used.
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Re: datum plane creation is unintuitive

Post by GeneFC »

GeneFC wrote: Wed Feb 13, 2019 4:32 pm I believe this is a "feature", not a "bug", but I do not fully understand why.
wmayer wrote: Wed Feb 13, 2019 6:32 pm
Thanks. Now I understand!

Gene
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bejant
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Re: datum plane creation is unintuitive

Post by bejant »

wmayer wrote: Wed Feb 13, 2019 6:32 pm In the offset dialog you will see the three axes X, Y and Z. They represent the local coordinate system of an object and not the world coordinate system. Having them in world coordinates doesn't make sense anyway because whenever you change the orientation of the object the datum plane is attached to you would have to change these values.

The tool tip of the X, Y, Z labels mention that it's in local coordinates but it might be good to have a label at the top of the group box that is always visible and clearly states how to interpret the axes.

One could also use letters like U, V and W but this doesn't really solve the confusion because in the property editor again the letters X, Y and Z are used.
I wonder if, to avoid confusion, when the user selects an object having a local coordinate system that is different than the world coordinate system, a secondary X,Y,Z axis indicator should also appear in the lower right corner (next to the existing world X,Y,Z indicator) that shows the local X,Y,Z axes of the selected item? When the object is de-selected this secondary indicator disappears.

Or maybe something similar could be done with the axis cross (View > Toggle Axis Cross)?

Just some ideas...
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