[Scilab-users] Sgrayplot/champ for non-regular grids

[philippe]

hi to all,

I realized that scilab function "Sgrayplot" (and other 2D plotting
functions like "champ") only accept "regular grids" that is
Sgrayplot(X,Y,Z) requires

size(Z)=length(X)xlength(Y)

while "surf" also accept non-regular ones with

size(Z)=size(X)=size(Y)

this pose substantial problems in some plots, compared to matlab/octave
behaviors, and it would be a nice feature that Sgrayplot and others
accept non-regular grid in the same way as "surf".

My problem started when I needed to plot a vector field "above"  a gray
plot, the usual way to do this is straight and simple :

dt=0.1;t=-1:dt:1;
[X,Y]=meshgrid(t,t);
Z=X.^2-Y.^2;// potential field
Vx=X;Vy=Y;//vector field
clf;
Sgrayplot(t,t,Z')
champ(t,t,Vx',Vy')// simple ... except the ' on Z,Vx,Vy :-)

but I need to do this for Z,Vx,Vy corresponding to a non-regular grid
(It comes from a Joukowski transform for those who want to know) so I
can't use anymore Sgrayplot/champ  and I try to replace them with
surf/xarrows

dt=0.1;t=-1:dt:1;
[X,Y]=meshgrid(t,t);//  <== in real life X,Y are non-regular
Z=X.^2-Y.^2;// potential field
Vx=X;Vy=Y;//vector field
clf;
// let's try to simulate Sgrayplot
surf(X,Y,Z);E=gce();E.thickness=0;E.color_flag=3;
A=gca();A.rotation_angles=[0,90];
// horrible hack to replace "champ"
xarrows([X(:)';X(:)'+dt*Vx(:)'],[Y(:)';Y(:)'+dt*Vy(:)'],[Z(:)';dt+Z(:)'],1)

If you compare both plot the second method isn't satisfying, because
vectors can be hidden by the surface (and code is complex!).

Can someone provide a work-arround to improve the result since changing
the specification of Sgrayplot/champ can't be done quickly.

sincerely yours,
Philippe