Re: Feature request: make line selection tool show dx/dy

Posted by Jan Eglinger on Jan 06, 2020; 1:31pm
URL: http://imagej.273.s1.nabble.com/Feature-request-make-line-selection-tool-show-dx-dy-tp5022813p5022814.html

Hi Adrian,

you might want to create a custom line selection tool for this. Here's
an example (mind the possible line breaks introduced by the mail client
- that's one of the reasons I prefer the image.sc forum over the mailing
list):


// Author: Jan Eglinger
macro "Kymograph Line Selection Tool - L1af1Ca00V0933Ve033C00fL1afaLfaf1" {
     var leftButton = 16;
     getCursorLoc(x, y, z, flags);
     x0 = x;
     y0 = y;
     while (true) {
         getCursorLoc(x, y, z, flags);
         makeLine(x0, y0, x, y);
         showStatus("dx: " + (x-x0) + "; dy: " + (y-y0));
         if (flags&leftButton==0) {
             return;
         }
     }
}






On 2020-01-06 12:43 PM, Adrian Daerr wrote:

> Hello,
>
> I frequently use the line selection tool to measure the speed on
> kymographs[1] (also known as spatio-temporal diagrams), which are images
> where one dimension (say the horizontal) is a spatial dimension, and the
> other (say the vertical) is a temporal dimension. A moving object or
> interface produces an oblique trace, whose speed is just the slope dx/dy
> (assuming, as above, that the y axis represents time).
>
> [1] https://en.wikipedia.org/wiki/Kymograph
>
> To get the speed or slope of a trace, I use the line selection tool to
> visually fit a tangent to this trace. This tool shows the angle of the
> line in the status bar of the main application window, and computing its
> tangent yields the slope in the chosen units.
>
> I wonder if it were possible for the line selection tool to show the two
> increments dx and dy of the line selection - that is the x and y offsets
> of the current point to the starting point -  'live' in the statusbar
> along with the other information ? The increments are more meaningful as
> measurements than the angle in my use case, and the calculations become
> less error-prone (e.g. when using the angle, depending on which
> dimension is the time, one must take either the tangent or the
> cotangent, and the wrong choice may go unnoticed for a while). Moreover
> the spatial and temporal measurement intervals - that is the length of
> the fitted line segment - are lost in this process, and thus estimating
> the uncertainty from the angle alone is impossible.
>
> If that makes the infoline too long, one could add to the line selection
> tool options (currently only line width) the possiblity to choose what
> data is shown (I am very rarely interested in the x/y coordinates of the
> cursor location when I use this tool for example, and would happily
> trade them for the dx/dy of the segment).
>
> I am aware of at least two work-arounds:
>
> 1) finishing the line selection (second mouse click) and doing a
> measurement with 'bounding box' selected will give me the desired
> increments as 'Width' and 'Height' in the measurement results table.
>
> 2) using the rectangle selection tool provides the increments between
> current and starting points as Width and Height in the statusbar, but
> fitting the invisible diagonal of the rectangle to the trace via just
> the two corners is much less reliable and reproducible than visually
> fitting a line to the entire trace.
>
> If there is an easy way of replacing/customising the status bar
> information via a macro or plugin, that could be an interesting and
> flexible solution.
>
> So this is merely a feature request to ease the workflow.
>
> Thanks for reading up to here,
> cheers,
> Adrian
>
> --
> ImageJ mailing list: http://imagej.nih.gov/ij/list.html

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