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Logic behind Sketch Orientation?

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Re: Logic behind Sketch Orientation?

Jonathan:

Yes every datum looks into the positive quadrant.  If I do an extrude I would expect it's positive to project into the positive quadrant.

As far as views go; if I place an object on a table if I look down on the object it would be considered the Top View.  If I look at the closest edge surface from the front of the table it would be considered the Front View.  If I look at the closest edge surface from the right of the table it would be considered the Right View.


The way views and datums are set up you always would look at what is closest to you and an extruded sketch would always extrude into the screen.


I'm sorry if my terminology is deficient.  I'm not sure what +ve would refer to.

Re: Logic behind Sketch Orientation?

Sorry, "+ve" and "-ve" are shorthand for "positive" and "negative".  I thought that was a standard abbreviation.

Your original problem seemed to be that 'Front' behaved differently to the other two views ("As stated above this only doesn't work with the FRONT VIEW.").  If you compare the plane front/back side (normal direction) to the CS_LOCAL axis directions, are all three aligned the same way?  I.e., are all three plane normals pointing in the same direction as the corresponding csys axis?  If not, then this is why Front behaves differently, and the solution is to make all three orientations the same.

Regarding extrude directions, from recollection I think that the default direction for 'additive' extrudes is out of the screen when viewing the sketch (so the opposite of the sketch viewing direction); for cuts, it's into the screen (the same as the sketch viewing direction).  But this is not necessarily the same issue as the sketch viewing direction.

(Your definition of the directions seems a little meaningless to me, btw, because I can place an object on a table any way up I like... the view directions in this case are locked to the object, so this doesn't help!  You also haven't said how the axes are oriented to the table.)

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Re: Logic behind Sketch Orientation?

Jonathan:  I believe what we are both saying is correct but are from the perspectives of opposing coordinate systems.  I set my datums and views up using the World Coordinate System and Creo uses the Right Hand Coordinate System.  I think both of us are scratching our heads in understanding where we are coming from but when I look at Creo's default coordinate system and apply what you say to it, suddenly this makes sense.  I'm not sure why people like working with this type of coordinate system, but if you were using this type of coordinate system it would be difficult to transition out.  Since most of the CAD world works in a different coordinate system my viewpoint is going to be a minority opinion, but it works great for seeing things in their true position.

I did submit a Idea Submission in regards to having a choice for World Coordinate System which might resolve the issue I've brought up with the Front View  Would like World View model display option

I'm going to try a couple tweaks to my template model to resolve the issue, but I'm thinking I'll just have to deal with it.

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Re: Logic behind Sketch Orientation?

Technically both have the same coordinate system (right hand), but PTC has chosen to name the planes associated with each direction differently.  Practically this means the PTC default looks like a "world coordinate system" tipped forward 90 degrees.

World CS (z up)

z_up.PNG

PTC Default (y up)

y_up.PNG

Again, by simply rotating the model to a z-up position, you can clearly see the CS really is the same, it's just the plane names that are different.

y_up_rotated.PNG

By the way, the z-out and y-up comes from 2D land (before 3D existed) and continues to this day in several different CAD platforms.

Now, while you can create a proper z-up start part with proper views, not everything inside Creo can be adjusted to look right.  There are still issues with shadows going the wrong way when viewing shading w/reflections, etc.

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Re: Logic behind Sketch Orientation?

Just for fun, here is a link showing Creo users are not the only ones with this issue:

User Interface: Global Coordinate System Orient... | SOLIDWORKS Forums

(What will really mess with your head is the fact that Windchill's default for thumbnail creation is Z-up.  You would think PTC could at least be consistent across their product line.)

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Re: Logic behind Sketch Orientation?

That is an interesting read Tom.

This does show that users would like to have the option to have the X and Y on the table with the Z direction pointing up.

You are correct that when CAD was introduced it was a 2D world and at that time there wasn't any issues related with having Z up on the screen.  When it became a 3D world it created the complications.

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Re: Logic behind Sketch Orientation?


Tom, "You would think PTC could at least be consistent across their product line" made me laugh a little....then cry. ;o)

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Re: Logic behind Sketch Orientation?

I just realized we've both already had this discussion:  Turned around with Coordinate System

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Re: Logic behind Sketch Orientation?

Indeed, it looks like we're just coming at this from different directions.  For me Thomas Braxton pretty much captured it in the other linked thread:

This is why I am still of the opinion that the default datums of start parts should not in general imply orientation in the absence of geometry. There are conceivable exceptions, however start model default datums should not have names like front, top, right IMO.

One work-around I've realised I use, is that I never hit the 'default orientation' button - I always use one of the other named views from our start part.

I also don't understand the issue with orientation when exporting, but then I'm working in automotive and we tend to agree our assembly origin (and orientation) before we start a project.  The default orientation when assembling is simply "X on X, Y on Y, Z on Z" - that makes sense to me.  I find myself more confused by Catia, which somehow appears to manage with no absolute frame of reference in an assembly - everything just seems to float in space!

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Re: Logic behind Sketch Orientation?

Jonathan:

In our case we got spoiled when we got the VX (now ZW) software because the view environment matched the orientation used in the machine shop, and our parts get manufactured in the same orientation.  We have tried to match the same environment with Creo.  (It works with some minor issues, just like Tom has also suggested).

We are a 3rd tier automotive supplier.  Most of our models are received from Catia as well.  We always wish the models could be supplied in the orientation it was built and not the vehicle assembly location.  Some of the parts don't have more than 1 feature that is flat so it is hard to line up for our purposes.

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