# Adjust Plot to Center on a specific point

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Patrick Scott 2020 年 12 月 8 日

I have a 2-body plot (Earth and Mars) and the center of the plot is not on one of the bodies. I would like to shift the center to be one mars. As in making the plot mars centric.
clc
clear
close all
earthrv =[91900278.4829176; -120935705.950185; 5320.0593002369; 23.22799727906; 17.9095930906743; -0.00087982431168286];
marsrv = [-1419159.59812317; 234896748.848865; 4957065.40583768; -23.310647752292; 1.91254780464408; 0.612032897279168];
tol = 1e-12;
tof_sc= [0 203*3600*24];
hold on
plot3(earthrv(1),earthrv(2),earthrv(3), 'o', 'MarkerFaceColor', 'green', 'MarkerSize',9)
plot3(marsrv (1),marsrv (2),marsrv (3), 'o', 'MarkerFaceColor', 'red', 'MarkerSize',9)
scrv = [earthrv(1); earthrv(2); earthrv(3); earthrv(4)+ 2.75; earthrv(5)+ 2.75; -0.00087982431168286+1.15]
iter = 0;
options = odeset('RelTol', tol, 'AbsTol', tol);
[t, xd3] = ode45(@twobody, tof_sc, scrv, options);
plot3(xd3(:, 1), xd3(:, 2), xd3(:, 3), '--', 'MarkerEdgeColor', 'k');
xlabel("X");
ylabel("Y");
zlabel("Z");
view(20, 20)
grid on
hold off
%% Functions
function [dvp, dva, TOF, delta_v] = hohman(r1, r2, mu)
vt1 = sqrt(-2*mu/(r1+r2) + 2*mu/r1);%is the periapse velocity on the transfer orbit
vc1 = sqrt(mu/r1);
vt2 = sqrt(-2*mu/(r1+r2) + 2*mu/r2);%the apoapse velocity on the transfer orbit
vc2 = sqrt(mu/r2);
dvp = abs(vt1 - vc1);
dva = abs(vt2 - vc2);
delta_v = dvp + dva;
TOF = pi*sqrt((r1+r2)^3 / 8*mu);
end
function [xd] = twobody (t,x)
muu = 1.327e11;
xd = [x(4:6); (-muu/norm(x(1:3))^3)*x(1:3)];
end

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### 回答 (1 件)

Cris LaPierre 2020 年 12 月 8 日

I'm not aware of a function for doing this, but what is at the center of a plot is controlled by the axes limits. With a little math, you can force mars to be in the center.
Here's one way of doing it
earthrv =[91900278.4829176; -120935705.950185; 5320.0593002369; 23.22799727906; 17.9095930906743; -0.00087982431168286];
marsrv = [-1419159.59812317; 234896748.848865; 4957065.40583768; -23.310647752292; 1.91254780464408; 0.612032897279168];
tol = 1e-12;
tof_sc= [0 203*3600*24];
hold on
plot3(earthrv(1),earthrv(2),earthrv(3), 'o', 'MarkerFaceColor', 'green', 'MarkerSize',9)
plot3(marsrv (1),marsrv (2),marsrv (3), 'o', 'MarkerFaceColor', 'red', 'MarkerSize',9)
scrv = [earthrv(1); earthrv(2); earthrv(3); earthrv(4)+ 2.75; earthrv(5)+ 2.75; -0.00087982431168286+1.15];
iter = 0;
options = odeset('RelTol', tol, 'AbsTol', tol);
[t, xd3] = ode45(@twobody, tof_sc, scrv, options);
plot3(xd3(:, 1), xd3(:, 2), xd3(:, 3), '--', 'MarkerEdgeColor', 'k');
xlabel("X");
ylabel("Y");
zlabel("Z");
view(20, 20)
grid on
hold off
%###########################################
% New code added to place mars in the center
dX = max(abs(marsrv(1)-xlim));
dY = max(abs(marsrv(2)-ylim));
dZ = max(abs(marsrv(3)-zlim));
xlim(marsrv(1)+[-dX dX]);
ylim(marsrv(2)+[-dY dY]);
zlim(marsrv(3)+[-dZ dZ]);
%###########################################
%% Functions
function [dvp, dva, TOF, delta_v] = hohman(r1, r2, mu)
vt1 = sqrt(-2*mu/(r1+r2) + 2*mu/r1);%is the periapse velocity on the transfer orbit
vc1 = sqrt(mu/r1);
vt2 = sqrt(-2*mu/(r1+r2) + 2*mu/r2);%the apoapse velocity on the transfer orbit
vc2 = sqrt(mu/r2);
dvp = abs(vt1 - vc1);
dva = abs(vt2 - vc2);
delta_v = dvp + dva;
TOF = pi*sqrt((r1+r2)^3 / 8*mu);
end
function [xd] = twobody (t,x)
muu = 1.327e11;
xd = [x(4:6); (-muu/norm(x(1:3))^3)*x(1:3)];
end

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