needs to get projection of one point from one x-axis to another

Hello. I have a problem with gui. I got a plot with 2 different scaling x-axes and one y-axis. I need to get position of point (created on red axis) in values of magenta axes. And then to create a plot using this point as a start on magenta axes. How can I do it?

[Aleksandra]

so magenta axes - xaxislocation, bottom

yaxislocation, left

red axes - xaxislocation, top

yaxislocatopn, right

Answer 1

[Geoff]

Have I understood correctly? You have xred and xmag which are two different ranges. You want to translate the x-coord from the red axis to the magenta axis without a visual change in position.

I assume that xred and xmag are both 1-by-2 vectors defining a min- and max-value. Assuming that your axis scale is linear, I'll first turn a point x into an axis-relative value with the red scaling (axis-relative being a number from 0 to 1 - ie normalised):

xrel = (x - xred(1)) / diff(xred);

Now, I'll reverse the calculation and translate the relative position into the magenta axis:

x1 = xmag(1) + xrel * diff(xmag);

Putting that together, to translate from one axis limit to another you could do this:

xlate = @(x,lim1,lim2) lim2(1) + (x-lim1(1)) * diff(lim2) / diff(lim1);

x1 = xlate(x, xred, xmag);

This will work if x is a vector, too.

[Aleksandra]

Thanks a lot!

I just didn't get what the lim1, lim2, lim2(1)?

[Geoff]

No problem: lim1 is the range of the 'from' axis, and lim2 is the range of the 'to' axis. The value lim2(1) is the first value (lower bound) of the 'to' range. You can get these range vectors directly off your axes by calling get(axishandle, 'XLim').

[Aleksandra]

It works now. Thanks.

[Geoff]

No problem. This question is still open. If I have answered your question, please accept the answer. If my answer was not satisfactory, and your own answer is better, please accept that instead.

Answer 2

[Aleksandra]

Finally, I used ginput(1) to get pixel location of desired point and then use this location as start point for new axes.