Thread Subject: patch created from isosurface hides plot3 inside the surface

Hi all,
I was trying to create patches from an isosurface from a
3-D array A (1 being inside the object, and 0 outside) using
the command:
patch(reducepatch(isosurface(x,y,z,A, 0), P))

Upon the surface creation, I was trying to use plot3 to plot
some of the datum points which is supposed to be on the
surface. However, the datum points always like to be shown
"inside" the surface, rather than half-half, or on the
surface. This makes visualization very difficult.

I guess the image below explains it all:
[url=points_hiding_inside_surface][img]http://img2.freeimagehosting.net/uploads/54addd07b2.png[/img][/url]
http://img2.freeimagehosting.net/uploads/54addd07b2.png

Is there any way I could get the plot more visible?

Thanks,
Abe

"Abe Lau" <abe@nonexistancegmail.com> wrote in message
<g1lv0n$6em$1@fred.mathworks.com>...
> Hi all,
> I was trying to create patches from an isosurface from a
> 3-D array A (1 being inside the object, and 0 outside) using
> the command:
> patch(reducepatch(isosurface(x,y,z,A, 0), P))
>
> Upon the surface creation, I was trying to use plot3 to plot
> some of the datum points which is supposed to be on the
> surface. However, the datum points always like to be shown
> "inside" the surface, rather than half-half, or on the
> surface. This makes visualization very difficult.
>
> I guess the image below explains it all:
>
[url=points_hiding_inside_surface][img]http://img2.freeimagehosting.net/uploads/54addd07b2.png[/img][/url]
> http://img2.freeimagehosting.net/uploads/54addd07b2.png
>
> Is there any way I could get the plot more visible?
>
> Thanks,
> Abe

Just wondering if any others had similar problem before, or
am I just creating the surface in a wrong way?

It looks to me that the datum points tends to be shown
"outside" of the surface on a convex surface, and "inside"
on a concave surface... wonder if it's a default behaviour,
or if I could change it.

I was thinking to shrink the volume before I create the
isosurface, but looks like if I wanna go that way, I will
need to loop through every images and shrink it, which is
quite time consuming (not to mention the model is changed)

Any help is much appreciated.

you can use alpha(0.1) to make the isosurface transparent

%%%%
.... alpha sets one of three transparency
properties, depending on what arguments you specify with
the call to this function.








"Abe Lau" <abe@nonexistancegmail.com> wrote in message
<g1lv0n$6em$1@fred.mathworks.com>...
> Hi all,
> I was trying to create patches from an isosurface from a
> 3-D array A (1 being inside the object, and 0 outside)
using
> the command:
> patch(reducepatch(isosurface(x,y,z,A, 0), P))
>
> Upon the surface creation, I was trying to use plot3 to
plot
> some of the datum points which is supposed to be on the
> surface. However, the datum points always like to be
shown
> "inside" the surface, rather than half-half, or on the
> surface. This makes visualization very difficult.
>
> I guess the image below explains it all:
> [url=points_hiding_inside_surface][img]
http://img2.freeimagehosting.net/uploads/54addd07b2.png
[/img][/url]
> http://img2.freeimagehosting.net/uploads/54addd07b2.png
>
> Is there any way I could get the plot more visible?
>
> Thanks,
> Abe

Thanks for your input Gianni.
Yes I have actually tried to set transparency to workaround
the problem, as you could probably tell from the screenshot
attached.

While this could be a workaround, the effect is far from
good unfortunately, especially when you only want to
illustrate what is on the surface, but not everything behind
it. I will need to set the alpha to a very low value to
"uncover" the datum points and this makes the entire surface
almost transparent (of cos, haha). More to say, if I would
like to export the figure in a vector format, all the
transparency will be removed :(

Any other idea?

"Gianni Schena" <schena@univ.trieste.it> wrote in message
<g3578h$djn$1@fred.mathworks.com>...
>
> you can use alpha(0.1) to make the isosurface transparent
>
> %%%%
> .... alpha sets one of three transparency
> properties, depending on what arguments you specify with
> the call to this function.
>
>
>

Any insight on this problem? or am I basically creating the
patches and plot incorrectly?

The summery now:
From a 3D volumetric array:
patch(reducepatch(isosurface(x,y,z,A, 0), P))

I want to plot some of the surface coordinates for
illustration, using "plot3"

However, many datum points (esp in concave area) got hidden
"inside" the model, even when the point size is huge, as
shown below:
http://img2.freeimagehosting.net/uploads/54addd07b2.png

Gianni suggested setting alpha to 0.1 to show the points,
but the model is then too transparent, displaying not only
the surface points, but everything. Problem with export
also, where transparency is not supported in vector-based
format.

PS: is this a proper newsgroup, and is top-post/bottom-post
preferred? can't find it in the rules, and I'm reading this
from the mathworks website also....

Thanks