DPI is an almost irrelevant number these days.
No - when it comes to print an image it definitely IS relevant . .
. How would you get an image on paper without printing dots on the paper?
Lets make it clear and simple: having a digital image (or a scan) means to have a heap of pixels, right? Yes.
Displaying the pixels means converting them to points/dots for making the pixels visible on devices, paper, screen and so on. Right? Yes.
So the first thought shooting hires-panos is:
HOW much zoom do i need/want for using it on screen?
HOW big do i want to print the pano?
Depending on these decisions choose your lens/camera and the way you shoot.
When i need a sphere for moderately deep zooms i use to choose an 85mm lens. This gives me 86000 x 43000px for an equirectangular image.
This amount of pixels tells me how big i can print the image - which means dpi. By default APG is set to .72dpi. Setting it to letÂ´s say 300dpi gives me a smaller amount of dpi for the print - but the amount of pixels stays the same.
This print still contains the 86000 x 43000 pixels . . . but the size of the print depends on what i set as dpi. Very simple.
Conclusion in the sense of photography (ANY photography): always use the best resolution you can afford to realize - which means sensorsize and focal-length to shoot with.
Downscaling an image always is possible without loosing quality (almost).
But upscaling an image definitely means a loosing quality - always.
Always render an image @100%. Always calculate before the shooting how much resolution you need in dpi for printing or displaying big.
If you want to print 20m x 4m you need to use a lens/camera which provides the amount of pixels you need for printing it at the needed size in dpi.
Basically itÂ´s that simple: bringing pixels to paper or displaying them anyhow needs dpi/ppi . .