| plotting data as it arrives using objects [message #44323] |
Mon, 06 June 2005 09:38  |
clive_cook59
Messages: 6
Registered: January 2005
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Junior Member |
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Hi,
I am trying to write an object based program which collects lidar data
and plots the data as it arrives. I previously did this with direct
graphics plotting each profile as it arrived, which would produce a
contour plot. This was done by using the plots command and by scalling
the data with a chosen colour table using the BYTSCL command.
I would like to do something similar with objects. I guess one way wold
be to create a new profile using the idlgrplot object however we would
be collecting several thousand lidar profiles over several hours and i
can't imagine that you could create as many objects.
I hope this is clear
many thanks
Clive Cook
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| Re: plotting data as it arrives using objects [message #44402 is a reply to message #44323] |
Tue, 14 June 2005 10:21  |
Rick Towler
Messages: 821
Registered: August 1998
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Senior Member |
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clive_cook wrote:
> Ok, i didn't do a good job of explaining myself. I've also done a
> little bit of research. Ultimately i'm looking to produce a contour
> plot (usually you can use the contour function in direct graphics or
> the idlgrcontour object). The idea is to produce this plot as data
> arrives, arriving approximately one profile every 2.5 seconds. Its a
> slow inefficient way to re-calculate the contour so in direct graphics
> i drew one profile at a time onto a plot using the plots command and
> scaling the colours to the data values (so a series of these profiles
> produces a contour plot however it is drawn on the fly).
>
> So now i am trying to do something similar with object graphics. I
> tried doing it by updating my data to the idlgrcontour object using
> contour->setproperty,data_values=new_data as new data arrives. The
> problem with this is as the new_data array increases in size the time
> taken to re-calculate the contour also increases, eventually it becomes
> far to slow. I'm looking for a way to do this in a more efficicent way.
O.K. Now you're making sense :)
First you'll want to get an idea if your design goals are practical.
Determine how many vertices you will have in your final surface. You
threw out some numbers a few posts ago but they don't really make sense
in this context. Will you have 1,000, 10,000, 1,000,000? For instance,
1,000,000 vertices may never draw quickly on your system regardless of
program design.
On my machine I noticed a few interesting things. I used the DIST()
function to generate some surfaces of different sizes and then looked at
the performance of the different IDLgr* objects which would be useful in
your case
First thing I noticed is that there is a *lot* of overhead in
IDLgrContour. Makes sense, a lot is going on. What was interesting was
that a filled contour took noticeably longer to re-draw than a
non-filled contour object + a filled surface object. You need to
determine if you need to use IDLgrContour or if IDLgrSurface or
IDLgrPolygon or some combination will be suitable.
Second thing I noticed was that even on my high end PC you aren't going
to contour 1,000,000 vertices quickly. It took almost 2 minutes to draw
the first instance of a *filled* contour with 50 levels. Contrast that
with about 2 seconds for a surface and 27 seconds for a surface plus
non-filled contour with 50 levels. Note that the N_LEVELS keyword has a
large effect on draw time.
Do you really need the contour lines?
Performance wise, IDLgrPolygon would be the best way to go as there will
be the least amount of overhead when updating data. As each profile
comes in you'll need to mesh that row of data and append the vertex data
onto your data array and the connectivity data onto your polygons array.
You can get the same color by value effect with texturing but you will
not have your contour lines. I have meshing code which would be of some
help.
Or you may find that you can live with an IDLgrSurface object plus a
non-filled IDLgrContour object. You may also find that in this case you
can live with updating your contour object less frequently (say every
10-20 profiles) to limit overhead. You'll still have the surface
object, the contour lines will just lag.
Determine what is possible with your hardware, if there are any upgrades
that you could make to speed along the process (at this point you're CPU
bound), and go from there.
-Rick
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