Default origin polarity is not consistent across planes

[brian_weinstein]

When I open up a new project, I've realized that when I go to place a sketch, the coordinate systems for each of the planes is not consistent. The positive and negative sides of each axis change depending on which plane I'm looking at. What's the rationale behind this?

First, let me say that I assume the Red, Green, and Blue axes markers for X, Y, and Z respectively follow the usual unit vector convention, where each of them is pointing in the positive direction. So, as we go through these pictures, we should be getting our sketch axes values to be consistent with that... for most of the cases we do, except for Z.

In each case, I'm about to assign a new sketch to one of the planes, and as I hover over the plane, Fusion puts axes units on the axes.

Everything is good until the XZ plane, where the sketch units FLIP IN THE Z AXIS. See the example below. 

What's going on here?

XY PLANE / TOP VIEW:

X - we get a -2.5 in the opposite direction of the Red X unit axis. Good!

Y - we get a 2.5 in the same direction as the Green Y unit axis. Also Good.

YZ PLANE / RIGHT VIEW:

Y - we get a -2.5 in the opposite direction of the Green Y unit axis. Good.

Z - we get a 2.5 in the direction of the Blue Z unit axis. Still good.

(also, it would be nice if the infinite axes in this plane were the same color as the unit axes)

XZ PLANE / FRONT VIEW:

X - We get a -2.5 in the opposite direction of the Red X unit axis. Nice.

Z - We get a 2.5 in the opposite direction of the Blue Z unit axis.... NOOOOOOOOOO.

(also, it would be nice if the infinite axes in this plane were the same color as the unit axes)

[davebYYPCU]

Couple of things, 

First, File origin has a front and back of the plane, depending on which side you select - that can happen.

Try selecting the other side of XZ.  Not camera side.

Second the Sketch grid is always 2d with red X and green Y, if not would be very confusing.

Eliminate all confusion, hide the grid (- timewaster), and use your own dimensions,

(Hint there are no negative dimensions)

Might help....

[jeff_strater]

why-is-my-sketch-text-appearing-upside-down 

"also, it would be nice if the infinite axes in this plane were the same color as the unit axes"

Those "infinite axes" are describing a different coordinate system.  They are the sketch coordinate system of the active sketch.  Those may or may not line up with the component coordinate system.  Red is always X, Green is always Y, and Blue is Z (when there is a Z - the sketch grid does not show Z).  So, the red axis of the sketch grid is the sketch X, and the green axis is the sketch Y axis.

[brian_weinstein · Accepted solution]

Ok, thanks! Your reply there was super helpful! https://forums.autodesk.com/t5/fusion-design-validate-document/why-is-my-sketch-text-appearing-upsid...

"also, it would be nice if the infinite axes in this plane were the same color as the unit axes"

Those "infinite axes" are describing a different coordinate system.  They are the sketch coordinate system of the active sketch.  Those may or may not line up with the component coordinate system.  Red is always X, Green is always Y, and Blue is Z (when there is a Z - the sketch grid does not show Z).  So, the red axis of the sketch grid is the sketch X, and the green axis is the sketch Y axis.

Ok, makes perfect sense now that I've read your other post. Thanks again!

For future readers:

There's some trade-offs going on here, and this was an orientation choice made by the design team. I'm not sure I would have done it the same way, but I understand the rationale. Basically, the rationale is that they wanted all the default extrusion directions to be in the octant surrounded by the XY, XZ, and YZ planes.

Here's the three default extrusions from each of the planes:

Apparently, in order to do this, the XZ plane has to have the local Y coordinate facing down, as shown in the other post. Geometrically, this is consistent with the other planes as it maintains the geometric relationships between the axes...

If I wanted to do it my way, where when you draw on the XZ plane, you'd have the positive X axis to the right, and the positive Y axis up, it would force the Z axis to be coming toward the camera, resulting in the default extrusion for the XZ plane to go in the other direction, like this:

I see the trade-offs here, I guess.