identify ppi/dpi of mobile devices

[dark_night]

Is there a way to identify the pinch-per-pixel of mobile devices?

The following example

var t = Ext.getBody().createChild({style:{width:'2.54cm'}},null,true);
dpi = t.offsetWidth;
Ext.removeNode(t);
allways gives me a value of 96 which seems to be a typical desktop-resolution.

[mitchellsimoens]

If you are trying to create display independent UIs, the use of em and then line-height is very useful.

[dark_night]

I need it for map scale so that e.g. 1 inch on a display of a mobile device equates 1 mile in the real world.

My app communicates with a map service that works with width/height, a bounding box and pixel density.

[mitchellsimoens]

Is it known the dimensions of the map when it is rendered? So say the map renders at 200px wide and 400px tall and the map is 1 mile wide by 2 miles tall

[dark_night]

The map service adjusts the given bounding-box (world coordinates) to the preferred resolution and pixel density so the resulting image will be different when changing pixel density.

So is it impossible to identify/evaluate the ppi from the device?