Posted by
Adrian Daerr-2 on
Jan 06, 2020; 11:43am
URL: http://imagej.273.s1.nabble.com/Feature-request-make-line-selection-tool-show-dx-dy-tp5022813.html
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/KymographTo 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
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