Simplify calculation of oblique map domain perimeter
|Target version:||Candidate for next minor release|
When using oblique projections we often wish to show the oblique domain on another map. This involves situations when -R -J is given with the -R<llx/lly/urx/ury>r specification. Turns out this is difficult to do in GMT without considerable scripting. My suggestion is to add a new option to mapproject, i.e. -W[nx/ny] which would require -R...r -J [ -C ] and no input file and simply write out the geographic coordinates of the oblique domain sampled as frequently as specify by the number of points along the two sides. Internally, we have 0,0 as the lower-left projected point, obtain X,Y of the upper-right projected point, then sample the four sides in a counter-clockwise direction and inverse project these coordinates to obtain lon,lat, which we then write to stdout.
Alternatively, it could be a new option for psbasemap to save the perimeter it draws in geographical coordinates to a specified file.