Stéphane,
There are two problems with this approach. The first one is that there is no way to know how many
disks cover a given point so the "heat map" would have only two levels: a given point
belongs or not to the impact area. Charles hasn't carified, but the term "heat map" he
used suggests a graded plot. The second problem is that you need to resource to a function not
directly available in Scilab so you need to install a toolbox. Moreover, you need to create an
intermediate file.
By the way, I always wondered why imread() isn't part of Scilab's core, as is
wavread(). Maybe image processing is a very specialized subject demanding a
complete toolkit to deal with it, but some basic functions like imread() or
imwrite() would be very handy to ensure easy interoperabilty with other
software packages.
It is also a pity that xs2bmp() cannot provide an array output with the pixel
data corresponding to the figure image (2x2x3 for color graphs).
Regards,
Federico Miyara
On 17/03/2023 12:17, Stéphane Mottelet wrote:
Hello,
I would propose this solution, inspired by my remark abour using xfarcs and the bitmap idea from
Frederico. The idea is to plot the disks then export the graph under a bitmap format, the read the
image back (needs "imread" e.g.from IPCV) then count the black pixels ("true"
value in x below). The ratio between black pixels and total number of pixels gives you the
proportion of covered area:
clf
n = 17;
xc = grand(1,n,"unf",0,5);
yc = grand(1,n,"unf",0,5);
radius = grand(1,n,"unf",0,1);
drawlater
arcs=[xc-radius
yc-radius
2*radius
2*radius
zeros(1,n)
zeros(1,n)+360*64];
st=ones(1,n);
a1 = newaxes();
a1.margins=[0 0 0 0];
xfarcs(arcs,st);
a1.data_bounds = [0,5,0,5];
isoview on
s=gcf().axes_size;
gcf().axes_size=[400 400]
drawnow
xs2bmp(0,"im.bmp");
x=imread("im.bmp");
disp(sum(x)/size(x,"*"))
S.
Le 16/03/2023 à 18:43, Federico Miyara a écrit :
Charles,
I assume the area of each impact point is circular (but it could be abapted for
other forms). Then you could start with a n*m matrix filled with zeros. Then,
according to a convenient scale, each impact point is approximated by a
component of the matrix. The horizontal and vertical positions (column and row)
will represent quantized coordinates.
Then, if the coordinates of an impact point ar p (column) and q (row) and the
radius of its impact area is R, expressed using the same scale, for column k =
(p - R):(p + R) you add 1 to the rows from q - sqrt(R^2-k^2) to q +
sqrt(R^2-k^2).
You repeat that for all impact points (with a for loop) and at the end you have
that each component of the matrix (which represent pixels) will be exactly the
number of overlapping areas at the location represented by the component. For
instance, if at component u, v you have 7, that means 7 impact areas contain
that component.
This could be adapted even to a graded impact area, replacing 1 by the result
of a function with a maximum at the center fading down to 0 at the perimeter of
the impact area
You must be careful near the boundary so that components don't exceed the
limits (for instance, not smaller than 1 or greater than n or m)
This is not probably the most efficient way, but assuming the impact area is
small it should work fine and reasonably fast for a few thousand impact points.
Regards.
Federico Miyara
On 16/03/2023 00:45, charles marcotte wrote:
Hello,
I have 2d scatter plot where each marker represents an impact point. The impact
point has a defined area.
1. I am trying to assign each point the impact area to visualize how much of
the surface is impacted.
Defining the marker size does not work because I change the scale between
simulations and I can't find a definition of the marker size vs diameter or
perimeter.
2. is there a way to calculate the overlap on the area through the chart with a
heat map for example?
Thank you
Charles
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--
Stéphane Mottelet
Ingénieur de recherche
EA 4297 Transformations Intégrées de la Matière Renouvelable
Département Génie des Procédés Industriels
Sorbonne Universités - Université de Technologie de Compiègne
CS 60319, 60203 Compiègne cedex
Tel : +33(0)344234688
http://www.utc.fr/~mottelet
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