Separation into two analysis regions via a crop circle

Hi everyone,

I need your advice today. I work on acquisitions in 3 dimensions of circular objects. My goal is to analyze the surface condition of these objects via mathematical parameters (Rp,Rv,Rz...).

Today, i've got a problem to analysis these acquisitions. In 3D, my camera acquires my objet but but also the table on which it's placed.If I take this plane into account, all the roughness parameter calculations are wrong !

This is why I would have to : make a circular crop of my object and I analyze via my parameters only the surface of my object. My code is following my message but I find this method approximative and it doesnt work :(.

Thanks in advance for your help.

%Inspired by @Image Analyst

close all;
clear all; 
clc;

%Open image

im_in=imread("zmap_14_48_03.png");   
[ymax,xmax,zmax]=size(im_in);     
figure(1)
imagesc(im_in)
title('Complete image')

%%
% Circular crop

Radius = 0;
while Radius == 0
	h = drawcircle('Color','r')
end
angles = linspace(0, 2*pi, 10000);
xcircle= cos(angles) * Radius + h.Center(1);
ycircle = sin(angles) * Radius + h.Center(2);
hold on;
plot(ycircle, xcircle)

% Creation of areas

area1= pi*Radius^2 + h.Center(1)+ h.Center(2) %Creation of a zone 1 composed of all point of my object
area2=im_in-area2 %Creation of a zone 2 composed of all points minus point of the objet

area2=nan;

%%
% Détermination de la ligne moyenne
Moyen1=mean(area1(:,:,:));
Moyen=mean(Moyen1);
 
%% Rought parameters calculs
%Rp
A=max(im_coupe(:,:,:));
A1=max(A);
Rp=A1-Moyen;
Rp1=max(Rp)

%Rv
B=min(im_coupe(:,:,:));
B1=min(B);
Rv=Moyen-B1;
Rv1=max(Rv)

%Rz
Rz=Rp1-Rv1;

%Rq
int1=0;
for yq1=1:echelley
    for xq=1:echellex
    int1=int1+im_coupe(:,:,:).^2;
    end
end

int11=mean(int1);

Rq1=sqrt((1./(echelley*echellex*int11)));
Rq2=sum(Rq1)/(echelley*echellex);
Rq=sum(Rq2)/echellex;

%Rsk
int2=0;
for yq1=1:echelley
    for xq=1:echellex
    int2=int2+im_coupe(:,:,:).^3;
    end
end

int22=mean(int2)
int222=mean(int22)

Rsk1=(1/Rq^3)*(1/(echelley*echellex*int222));
Rsk2=sum(Rsk1)/(echelley*echellex);
Rsk=sum(Rsk2)/echellex;

%Rku

int3=0;
for yq1=1:echelley
    for xq=1:echellex
    int3=int3+im_coupe(:,:,:).^4;
    end
end

int33=mean(int3)
int333=mean(int33)
Rku1=(1/Rq^4)*(1/(echelley*echellex*int333));
Rku2=sum(Rku1)/(echelley*echellex);
Rku=sum(Rku2)/echellex;

Results=[Rp1;Rv1;Rz;Rq;Rsk;Rku]