Plane plotted with fimplicit3 fails to render

load data E C ax
planefun=@(x,y,z) E(1)*x+E(2)*y+E(3)*z+E(4);

In the plot below, I successfully plot a point C and try to superimpose, with fimplicit3, the plot of a plane described by planefun. Since C nearly satisfies the plane equation,

planefun(C(1), C(2), C(3))

ans = -2.8422e-14

I think I should be able to see a portion of the plane in the figure (and it should pass through C), but I do not. Why?

plot3(C(1), C(2),C(3),'x'); axis(ax); hold on

fimplicit3(planefun,ax); hold off

Answer 1

[Matt J]

MathWorks Tech Support has classified this as a bug (Case #06788114)

[Adam Danz]

Thanks for reporting this, @Matt J. As you've discovered in another thread, this bug was fixed in R2024b.

Answer 2

[akshatsood]

Hi @Matt J,

I have noticed that you are experiencing difficulties with the 'fimplicit3' function during plotting. After attempting to replicate the issue, I encountered similar behavior. It appears that the problem stems from the axis limits defined by 'ax'. The 'fimplicit3' function requires an adequate range to properly visualize the surface where f(x,y,z) = 0 intersects the level f=0. In your instance, the provided 'ax' limits were insufficient, preventing the curve from rendering correctly.

Below is the revised code snippet with appropriate adjustments.

load data E C ax
planefun=@(x,y,z) E(1)*x+E(2)*y+E(3)*z+E(4);

plot3(C(1), C(2),C(3),'x','LineWidth',2,'Color','r'); 
hold on

f = fimplicit3(planefun,[-250 0]); 

f.EdgeColor = 'none';
f.FaceAlpha = 0.8;

hold off

Have a look at the following references for a better understanding

https://in.mathworks.com/matlabcentral/answers/2017881-why-fimplicit3-draw-the-same-function-differently

I hope this helps.

[Matt J]

Hi @akshatsood,

I do thank you for undertaking to study this problem. However, I don't think the span of the axes could be the issue. Here is a modified example with the same axis range, except that C has been translated to (0,0,0). The plane renders fine,

load data E C ax

ax=ax-repelem(C',2);

planefun=@(x,y,z) E(1)*x+E(2)*y+E(3)*z;

plot3(0,0,0,'x','LineWidth',2,'Color','r');
hold on

f = fimplicit3(planefun,ax); 
f.EdgeColor = 'none';
f.FaceAlpha = 0.8;

hold off