Re: Filling area under a curve

Hi,

 I suggested this approach because the description you made seemed close to this new functionality, but it may well be that you need something else. Can you send me a small *running* example showing what you do ?

Thanks, O.Couet

On Thu, 8 Jun 2006, Alexander Wagner wrote:

> On Wed, Jun 07, 2006 at 05:36:41PM +0200, Olivier Couet wrote:
>
> Hi!
>
> > I have recently implemented this in TGraph. See
> > $ROOTSYS/tutorials/graphpolar.C
> > This has been introduced in the last ROOT release. See:
> > http://root.cern.ch/root/Version511.news.html
>
> Just finished compiling it and tried your example. But I do
> not see how to use it in my case. My problem is, that I have
> something like z=f(x,y) and the area that I want to shade is
> "everything below z=excl". Additionally I can not easily
> solve f(x,y) for x or y analytically. That's why I used a
> TH2F to raster the area. Did I miss something? Maybe there
> is a way to extract the proper contour line easily into
> arrays so I can fill it into a TGraph? Did I miss that?
>
> Thanks in advance!
>
> > -----Original Message-----
> > From: owner-roottalk_at_pcroot.cern.ch
> > [mailto:owner-roottalk_at_pcroot.cern.ch] On Behalf Of Alexander Wagner
> > Sent: Wednesday, June 07, 2006 5:13 PM
> > To: Roottalk
> > Subject: [ROOT] Filling area under a curve
> >
> > Hi!
> >
> > In some of my plots I want to show an excluded area by just shading it
> > in gray. To this end I tried the following
> >
> > ----------------------------------------------------------------------
> > TH2F *Shade = new TH2F("excl", "", xbins, xmin, xmax, ybins, ymin,
> > ymax);
> >
> > for( Double_t x = xmin; x < xmax; x += (xmax-xmin)/xbins) {
> > for(Double_t y = ymin; y < ymax; y += (ymax-ymin)/ybins) {
> > val = curve(y, x);
> > if (val <= excl) {
> > Shade->SetBinContent(
> > Shade->FindBin(x,y), 500);
> > }
> > else {
> > Shade->SetBinContent(
> > Shade->FindBin(x,y), 0);
> > }
> > }
> > }
> > Double_t contours[1];
> > contours[0] = excl;
> > Shade->SetContour(1, contours);
> > Shade->Draw("cont4");
> > ----------------------------------------------------------------------
> >
> > Now, unfortunately root fills the area _above_ the curve in black (I did
> > not even find how to change that colour) and not the one below. I always
> > get it displayed in white, wheras I'd like something like gray70.
> > Actually the area above the curve should be transparent so that I could
> > Draw("cont4,same"), above another graph. Searching arround did not give
> > me a clue (though I came accros some other interesting things ;)
> >
> > Does anybody have a hint how to do this?
> >
> > Many thanks in advance!
> >
> > (Running root 5.10/00 @debian sarge.)
> >
> > --
> >
> > Kind regards, / War is Peace.
> > | Freedom is Slavery.
> > Alexander Wagner | Ignorance is Strength.
> > |
> > | Theory : G. Orwell, "1984"
> > / In practice: USA, since 2001
>
>

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