How would I position a UI view relative to the center of the screen, no matter the orientation?
Do I use the size_to_fit() function?

ui.center?

Do I have to make the ui view a sub view of a larger view? If so, how will that view be oriented when the iPad is rotated (sounds too complex to be the solution).

I am trying to make the view show up in the center of the screen, and scale to fit horizontally.

The easiest would be to use the auto-resizing inspector in the UI editor (or flex attribute when you do this from code). For centering a view vertically and horizontally in its parent, it should be LRTB (flexible left, right, top and bottom margins). For a view that stretches horizontally, and is vertically centered, it should be WTB. You can experiment with this in the UI editor (there's an animated preview to help you get an idea of the effect of different settings).

Okay, it is flexing when I rotate the ipad, but what do I set the popover_location parameter of the UI.present() function to, to center the UI in the center if the screen when I run the workflow.

It would seem that there is a constant for the screen's center, without having to use another UI element as the parent. This way, if someone is using a different screen size, it will take the dimensions of the screen and divide both the height and width by two, and then center at those coordinates.

To center my button in a parent view I had to do:

button.center = (window.width/2,window.height/2)

But the window itself, I want to center in the screen, No matter what screen size or orientation.

Edit

I found ui.get_screen_size(). How do I get the length component separate from the height component?

You can't really do that with a popover because it's currently not possible to get the current orientation. You might want to consider using a sheet instead...

Could I resize the dimensions of a sheet?

Also, I tried this:

popover_location=(ui.get_screen_size()[0]/2,ui.get_screen_size()[1]/2)

And it almost works. I used it along with flex too.

The portrait orientation is off, but, well take a look

Hmmm! I just saw that the screen size function would locate the arrow of the popover at the center! not the center of the popover. That is why it is off.

While there is nit an easy way to get orientation, if the keyboard frame is displayed, you can use ui.get_keyboard_frame to determine the current orientations width.

Take that back...
ui.WebView().eval_js('window.orientation')
Does give you orientation.

Okay. Thanks. I put this one on hold. I may pick it up later. Thanks!

I have picked this back up:

import ui
import workflow

screen_size = ui.get_screen_size()
screenX = screen_size[0]
screenY = screen_size[1]

window = ui.load_view()
window.flex = "WL"
window.height = 200
window.width = screenX
window.present("popover",False,(screenX,(screenY/2)))


view = window['view2']
view.text = workflow.get_input()

Now I have to add the orientation

See:
here

This includes a 1 pixel webview, which is used to get orientation, see e.g. line 61 and following for the possible values