Formatting of coordinates?

Question

In case I want to describe the pixels of a picture with cartesian coordinates, how would I properly typeset the coordinates? Is p_\mathrm{x}, p_\mathrm{y} correct or rather c_x, c_y? x and y represent the global cartesian coordinates -- again: italic or not?

Answer 1

I’ll always set them in italic since they are kind of variables. The upright font is used for constant values like Euler’s e etc., functions like the Sine or texts like “min”, “max” which are available as macros (\min and \max)^*, “start” or “eff[ective]” In the latter case I recommend to use the \text macro from amsmath (or via mathtools).

_{* See Count Zero’s comment}

Some examples

p_x = 3.5
p_\text{max} = 4
p_{x,\text{max}} = 5
p_\text{min} = \mathrm{e}
p_0 = \sin(\pi)
t_\text{start} = 2\,\mathrm{s}% better use siuntix!
U_\text{eff} = U_0/\sqrt{2}% I recommend to define \newcommand{\eff}{\text{eff}} to use
u_\eff = U_0/\sqrt{2}

Just a thought: I wonder why you need the p? I’d use $x=1$ and $y=2$ or $\vec{p}=(1,2)$ if using p as a vector I’d “access” it’s coordinates–like you did–with p_x and p_y.