| automatic placement of legend in 2-D graph [message #58172] |
Mon, 21 January 2008 12:26  |
Jean-Paul Davis
Messages: 17
Registered: March 1998
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Junior Member |
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I use a legend object in a separate model object to show a legend on a
2-D graph consisting of up to six plot objects. Currently I set the
position of this legend once and leave it there. Of course, changes
to the data or zoom scale can cause one or more of the plot object
curves to run right through the legend.
Does anyone have ideas for an easy way to automatically determine the
"best" placement of a legend? Using information on the axes ranges,
legend object boundaries, and plot data themselves, I might be able to
do some fancy calculations involving areas in a plane, probably
limiting myself to a set number of standard positions and picking the
least offensive. But this could be easier if there were a way to
determine the intersections of various objects in a particular view.
I'm interested in ideas related to either approach.
Jean-Paul
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| Re: automatic placement of legend in 2-D graph [message #58290 is a reply to message #58172] |
Thu, 24 January 2008 11:30  |
Jean-Paul Davis
Messages: 17
Registered: March 1998
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Junior Member |
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Okay, so I came up with an idea on my own that should work, but it
appears impossible to implement using the IDLgrLegend object. Yeah, I
know the simplest answer is to write my own Legend object (or use
someone else's), but that's probably not the simplest course of action
for me.
Anyway, here's the problem. I cannot get the IDLgrLegend object to
recompute its dimensions with changes in the containing view object's
viewplane rectangle. The heirarchy is rooted at this view object,
which contains two model objects, one for the plot and axes objects,
the other for the legend (so I can translate the legend around
separately from the plot and axes objects). The dimensions returned
by IDLgrLegend::ComputeDimensions or IDLgrLegend::GetProperty(xrange,
yrange) are correct for the viewplane rectangle set when the IDLgrView
object is initialized, but never change after that, regardless of the
setting of IDLgrLegend's Recompute property and regardless of how many
times I redraw the window after subsequent changes to the viewplane
rectangle. Here is an example to show this:
ofont = obj_new('IDLgrFont', 'Helvetica', size=16.0)
oxtitle = obj_new('IDLgrText', string='X-AXIS TITLE', recompute=2,
font=ofont)
oxaxis = obj_new('IDLgrAxis', direction=0, location=[9999,0,0.01],
title=oxtitle)
oxaxis -> getproperty, ticktext=oxtlab
oxtlab -> setproperty, , recompute=2, font=ofont
omodel = obj_new('IDLgrModel')
omodel -> add, oxaxis
olegend = obj_new('IDLgrLegend', item_linestyle=[0], item_name=['Test
Legend'], font=ofont, glyph_width=3.0, gap=0.3)
olegend -> setproperty, recompute=1 ; according to documentation, this
cannot be set by init
olegmod = obj_new('IDLgrModel')
olegmod -> add, olegend
oview = obj_new('IDLgrView', viewplane_rect=[0.0,0.0,1.0,1.0])
oview -> add, omodel
oview -> add, olegmod
owin = obj_new('IDLgrWindow', graphics_tree=oview)
owin -> draw
lsize = olegend -> computedimensions(owin)
print, lsize
oview -> setproperty, viewplane_rect=[-0.2,-0.2,1.4,1.4]
owin -> draw
lsize2 = olegend -> computedimensions(owin)
print, lsize2
If IDLgrLegend were recomputing it's dimensions, then I'd expect
lsize2 to be different from lsize (the legend is "wider" in the
normalized coordinates indicated by oxaxis object after increasing the
viewplane rectangle). Has anyone seen this or have a work-around?
Jean-Paul
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| Re: automatic placement of legend in 2-D graph [message #58491 is a reply to message #58172] |
Wed, 30 January 2008 14:49 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Jean-Paul Davis writes:
> I thought I would share this in case someone finds it useful. After
> spending a shameful amount of time barking up wrong trees, I finally
> hit on a very simple solution to (semi-) automatic legend placement:
>
> 1. determine the legend's boundaries in device coordinates (i.e.,
> pixels in the window)
> 2. hide the legend and redraw
> 3. get the window's image_data property
> 4. loop through possible legend positions (in device coordinates) to
> find one that has the fewest (preferably zero) non-background-color
> pixels in the region of the image defined by the legend boundaries
> 5. translate the legend accordingly, unhide it, and redraw
Now *that* is what I call a good algorithm. Simple enough even
I can understand it! :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming (www.dfanning.com)
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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| Re: automatic placement of legend in 2-D graph [message #58492 is a reply to message #58285] |
Wed, 30 January 2008 14:44 |
Jean-Paul Davis
Messages: 17
Registered: March 1998
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Junior Member |
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I thought I would share this in case someone finds it useful. After
spending a shameful amount of time barking up wrong trees, I finally
hit on a very simple solution to (semi-) automatic legend placement:
1. determine the legend's boundaries in device coordinates (i.e.,
pixels in the window)
2. hide the legend and redraw
3. get the window's image_data property
4. loop through possible legend positions (in device coordinates) to
find one that has the fewest (preferably zero) non-background-color
pixels in the region of the image defined by the legend boundaries
5. translate the legend accordingly, unhide it, and redraw
Jean-Paul
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