Hi Ryo,Well, sort of. Where you say "the lower left corner", you mean the lower left intersection of the plot axes.
I think it's easier to think of all of these symbols as lengths. ppl$xorg, ppl$yorg are the distances measuring the lower and left-hand margins, in "plot inches". ppl$xlen and ppl$ylen are the axis lengths, measured in "plot inches". These are defined at any time after either a plotting command or a plot/set command is issued, and they do not change. If you are drawing in a viewport, they are relative to the lower left corner of the viewport.
Historically, when we added the colorkey positioning arguments to SHAKEY, it was thought clearer to position it relative it to the lower corner of the plot "page" rather than relative to the corner of the plot axes. We thought this makes it easier to plot in a viewport and put the color key anywhere on the page. If you are moving the color key around, then those locations are measured from the corner of the page or viewport. Here's an example, where the last argument given is the location of the top of the color key, at the lower edge of the viewport.
use levitus_climatology set view uppershade/title="In viewport, shakey located at bottom of viewport"/set temp[k=1]
ppl shakey,1,0,0.1,2,,,,,,0 ppl shadeWe are only talking about LABEL and SHAKEY here. /USER or /NOUSER is only applied to LABEL commands, not to any other Ferret plot commands or PPLUS plot-customizing commands. If LABEL is done in /USER units (the default setting), one doesn't have to worry about all of this.
so, a bit of new documentation is needed for the LABEL/NOUSER and SHAKEY arguments, and maybe an FAQ.
Ryo Furue wrote:
Thank you, Ansley, for the detailed explanation. | The difference is in how the different commands use these symbols, | not in the values at different times. The values are the same | whether after set_up is issued, or after a plot command is | finished. I see. In other words, the "nouser" coordinates differ fromcommand to command.After set_up is issued and before the plot command is finished, the lower-left corner is (xorg, yorg). This applies to SHAKEY. On the other hand, for the LABEL command, the lower-left corner is (0,0), not (xorg, yorg), in the nouser coordinates. The width and height of the plot, however, are xlen and ylen for both cases. That seems to mean that we should document these things for each command that handles nonuser coordinates. | LABEL positions the labels relative to the origin, as it is (often) | used for positioning labels inside the box formed by the coordinate | axes, and it can be used with USER coordinates, to position a label in | terms of world coordinates such as degrees. As an aside, USER coordinates are often convenient for LABEL, but you prefer NOUSER ones when you want to place your labels at the same locations (in the paper coordinates) regardless of the size (in USER coordinates) of the plotting region. Regards, Ryo