How do I specify pixel dimensions for an app icon designed in Apple’s Keynote? [closed]

When submitting an app to Apple’s App Store you must provide an icon to represent your app. At a minimum, you must have an icon (in PNG format) that is 1024 pixels x 1024 pixels.

I designed my logo using the Keynote app. It was a surprise to find that Keynote no longer supports “pixel” as a unit of size. That is, when you go to:

Keynote -> Settings… -> Rulers -> Ruler Units

the only units in the dropdown box are “Points”, “Centimeters” or “Inches”.

Initially I thought that I could just use a conversion factor, based on the fact that my display has a 224 pixels/inch resolution. But there seems to be a layer of abstraction in Keynote, since the app allows you to specify the slide size and you can scale any slide up or down in size arbitrarily using pinch gestures. It isn’t clear what the conversation factor should be.

So, is there a way to create an object in Keynote and get it exported to a specific size in pixels? Many thanks!