Feature request: allow for specifying origin of X1 to be the same as that of X2

[p-costa]

I believe this is a feature of the plot digitizer tool, which is quite convenient. Normally for X-Y plots, the origin of the X and Y axis is the same, so perhaps it would be nice to have an option that allows choosing a single point for the origin of both X1 and X2

edit: this seems related to #222

[nbehrnd]

Both X1 and X2 are points, defining direction and scaling of the same X axis. From the remainder shown prior to the alignment of axes, I infer to define the intersection of the X with the Y axis as their respective origin however would demand X1 = Y1 = 0.

From a practical point of view, I actually like to chose explicitly if reference point 1 and 3 (or X1, Y1) are superimposed, or not. Agreed, often the narrative is to set local variations into the context of the bigger picture (as seen in some of Edward Tufte's work, too), such as here:

(source)

Sometimes, though, the narrative is about the change of variation rather than the variation itself, where I encounter broken ordinate axes like the following

(ibid.)

or an interrupted abscissa in time lines (not as important as the Keeling curve):

(source)

Thus I think your suggest would fit well as an additional functionality if the digitizer would automatically interpret the explicit definition of three reference points 1, 2, and 4 (in current counting X1, X2, and Y2) as «X and Y axis intersect at x = y = 0». This would require i) the menu «Axis Calibration Complete», now displayed after defining the fourth point, to appear already after putting the third point on the canvas. And ii) to offer a calibration matrix to hold either only two adjustable reference values other than the fix x = y = 0 already grayed-out: