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Re: Save 2D conversion matrix [message #46152] Mon, 07 November 2005 12:19 Go to previous message
R.Bauer is currently offline  R.Bauer
Messages: 1424
Registered: November 1998
Senior Member
David Fanning wrote:

> Peter Albert writes:
>
>> I am currently working on the display of climate datasets. One window
>> shows a map with e.g. some monthly mean values. My plan now is to let
>> the user pick a location using CURSOR, and then to display a time
>> series at the chosen point in a second window. O.k., I can get the
>> latitude / longitude of the chosen point using CONVERT_COORD, then I
>> can pick the appropriate time series and plot it in the second window.
>> However, if I am now going back to the map window, the correlation
>> between device and data coordinates is of course gone. If it was 3D
>> data, I would use T3D, but this is plain 2D data and don't see the
>> appropriate feature in the documentation. Any help which would save me
>> from re-drawing this map over and over again would be appreciated.
>>
>> N.b. this is all done using direct graphics. Is this finally the reason
>> to go ahead and read the manual about OO graphics?
>
> Object graphics is certainly overkill, but I would suggest
> you learn a little widget programming (seriously, the CURSOR
> command!? Sigh...).
>
> Benjamin's suggestion to save and restore the system variables
> is a good one, but it has always struck me as inelegant. Which
> variables, after all, did you really need to restore the
> coordinate system? It surely couldn't be ALL of them!
>
> So I spent a couple of days experimenting until I found out which
> ones I needed. (I was actually trying to find out which ones
> had to be set so I could establish a data coordinate system without
> going to the trouble of actually drawing a plot.) It turns out
> that these four pieces of information are needed to establish
> the data coordinate system: !X.S, !Y.S, !X.Window, and !Y.Window.
> Plus, the current window has to be the one your plot is in. (Not
> a given, always, in widget programming unless you explicitly
> make it so.)
>
> I found out that I could easily establish a data coordinate
> system for *any* window if I knew the X and Y range of the
> coordinate system and the location of the coordinate system
> in the window (i.e., its position). (I simply constructed the
> scaling parameters normally found in !X.S and !Y.S from the
> range and position.)
>
> So, even if you still save *everything*, it feels good
> to know what it is in that mess you really need. :-)
>
> Cheers,
>
> David
>

Hi David,

sometimes we would need !x.type of value 3 too. e.g. if we want to use
Map_Continents again. And probably we would need some more from !map,
from !p the transformation matrices and so on.

cheers
Reimar

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