You would be so happy working with the other side of computer graphics and my little buddy - the left-hand csys. This sets the origin at the top left of the screen, X positive to the right, Y positive down, and Z positive out of the screen.
Why in the world ... Because that's the way the pixel clock and the line counter works in typical raster screens, scanning left to right and top to bottom. Of course the electron beam is positively coming towards the viewer. I think this was the way that most screen graphics software is still - the locations are all positive, measured from Upper Left. The only exception I recall was for TrueBasic which moved to Lower Left.
Some programs, like POV Ray, allow changing the sense of the global CSG from right hand to left hand. If nothing else, it makes mirroring object easier.
Sorry I haven't piped in. I'm in the middle of a surprise rush job that has to be done this week.
Top view to us would coincide to the direction that the part would be inserted into a die.
Apparantly the normal part model datums are 90 degrees to the way they are in the MFG_CAST. I believe that's why when we export to the default datum they are 90 degrees off.
We would like our part model datum orientation to match the MFG_CAST orientation.
Paul, if you create a mapkey to orient a new CSYS to the orientation you want for your export, most export dialogs will let you choose another CSYS to export to. This should resolve your immediate problem for existing development.
The default of the system will always be different if the two are not identical already. Therefore, the only way is to use a re-oriented CSYS for export. This can be built into a start part for future development.
As the previous discussion concluded, the top down (looking down along Z and calling it TOP) is a holdover from early CAD where it mimics a drafting board.
Not exactly. The positive Z-axis coming towards you or "out of the screen" is the holdover from 2D board drawings. Z-up is more common when thinking in 3D space or "world coordinate system" where Z is positive moving away from the center of the earth.
Best analogy I can think of is the floor plan of a building. It's drawn in the X-Y plane. As soon as you rotate it down (set it flat on the ground) and add height to it you are building in the Z direction.
My bias (and I definitely have one) comes from creating models that were later programmed in Pro/NC for a vertical machining center (Z was up in the mill). Keeping the built-in CS aligned with how the parts would sit in the mill just made everything simpler. I also spent some time with Catia which also is Z-up.
I found this little quote that I liked here:
"Having a X-axis as horizontal and Y axis as Up direction is common way to represent 2D-space. But 3D-space is commonly represented in physics and other natural sciences so that if you think about a map in a table, Z-axis points up towards you (or sky) from map, X- points to east, Y points to North."
And a picture from Wikipedia:
If you already have a coordinate system that agrees with how you want the part oriented in the die, simply select that CS when exporting. The selecting of the CS can easily be recorded in a mapkey to simplify the export process.
True. There is a lot against convention when you add in other disciplines.
At some point you have to throw away Cartesian coordinates and replace them with spherical.
Image "thinking" in spherical coordinates! And yes, I know scientists that do. They couldn't design a deck if their lives depended on it.
I have always see X-Pos going towards the back of the car with Y Pos to the right and Y Neg to the left. Z Pos is still up going with the right hand rule.
That would be a top down with car facing left orientation as the "primary".
Okay, I take back my claim to and possible convention existing!
"Now which way was up again? OUCH! Wrong way..."