在matplotlib

Question

我在python和zorder中苦苦挣扎。我正在使用matplotlib制作具有3个相关元素的3D图：一个行星的surface_plot，该行星周围的surface_plot个环和一个contourf图像，该图像显示了投射到该行星上的阴影戒指。

我希望这些图形准确地显示这种情况在现实生活中的样子，环在行星周围旋转，阴影在适当的位置横穿环。如果阴影在给定POV的行星后面，我希望阴影被行星遮挡，反之亦然，如果阴影在给定POV的行星前面，则相反。

需要明确的是，这只是一个分层问题。我已经正确绘制了行星，环和阴影。但是，阴影永远不会显示在地球前面。它的作用就好像行星正在“遮挡”阴影，即使在分层方面应该将行星置于阴影之下。

我已经尝试过用zorder来思考的每件事，并重新排列绘制各种绘图元素的顺序。环确实显示在行星的前面，但是阴影不会出现。

我的实际代码很长。这里是相关的部分：

图设置：

def setup_saturn_plot(ax3, elev, azim, drawz, drawxy,view):
    ax3.set_aspect('equal','box')
    ax3.view_init(elev=elev, azim=azim)
    if(view=="top" or view == "Top" or view == "TOP"):
        ax3.dist = 5.5
    if(view=="star" or view == "Star" or view == "STAR"):
        ax3.dist = 5.0 #4.5 is best value
    proj3d.persp_transformation = orthographic_proj

    # hide grid and background
    ax3.w_xaxis.set_pane_color((1.0, 1.0, 1.0, 1.0))
    ax3.w_yaxis.set_pane_color((1.0, 1.0, 1.0, 1.0))
    ax3.w_zaxis.set_pane_color((1.0, 1.0, 1.0, 1.0))
    ax3.grid(False)

    # hide z axis in orthographic top view, xy axes in star view
    if (drawz == False):
        ax3.w_zaxis.line.set_lw(0.)
        ax3.set_zticks([])

    if (drawz == True):
        ax3.set_zlabel('Z (1000 km)',fontsize=12)

    if (drawxy == False):
        ax3.w_xaxis.line.set_lw(0.)
        ax3.set_xticks([])
        ax3.w_yaxis.line.set_lw(0.)
        ax3.set_yticks([])

    if (drawxy == True):
        ax3.set_xlabel('X (1000 km)',fontsize=12)
        ax3.set_ylabel('Y (1000 km)',fontsize=12)

行星：

def draw_saturn(ax3, elev, azim):
    # Saturn dimensions
    radius = 60268. / 1000.
    radius_pole = 54364. / 1000.

    # draw Saturn
    phi, theta = np.mgrid[0.0:np.pi:100j, 0.0:2.0*np.pi:100j]
    x = radius*np.sin(phi)*np.cos(theta)
    y = radius*np.sin(phi)*np.sin(theta)
    z = radius_pole*np.cos(phi)

    line3 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=5, shade=False, lw=0.25)
    #line3 = ax3.plot_wireframe(x, y, z, color="w", edgecolor='b', rstride = 5, cstride=5, lw=0.25)

    ax3.tick_params(labelsize=10)

戒指：

def draw_rings(ax3, elev, azim, draw_mode):
    # Saturn dimensions
    radius = 60268. / 1000.

    # Saturn rings
    dringmin = 1.110 * radius 
    dringmax = 1.236 * radius 
    cringmin = 1.239 * radius 
    titanringlet = 1.292 * radius 
    maxwellgap = 1.452 * radius 
    cringmax = 1.526 * radius 
    bringmin = 1.526 * radius 
    bringmax = 1.950 * radius 
    aringmin = 2.030 * radius 
    enckegap = 2.214 * radius 
    keelergap = 2.265 * radius 
    aringmax = 2.270 * radius 
    fringmin = 2.320 * radius 
    gringmin = 2.754 * radius 
    gringmax = 2.874 * radius 
    eringmin = 2.987 * radius 
    eringmax = 7.964 * radius 

    if (draw_mode == 'back'):
        offset = -azim*np.pi/180. - 0.5*np.pi
    if (draw_mode == 'front'):
        offset = -azim*np.pi/180. + 0.5*np.pi

    rad, theta = np.mgrid[dringmin:dringmax:4j, 0.0-offset:1.0*np.pi-offset:100j]
    x = rad * np.cos(theta)
    y = rad * np.sin(theta)
    z = 0. * rad
    line1 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=25, shade=False, lw=0.25,alpha=0.)

    rad, theta = np.mgrid[cringmin:cringmax:4j, 0.0-offset:1.0*np.pi-offset:100j]
    x = rad * np.cos(theta)
    y = rad * np.sin(theta)
    z = 0. * rad
    line2 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=25, shade=False, lw=0.25,alpha=0.)

    rad, theta = np.mgrid[bringmin:bringmax:4j, 0.0-offset:1.0*np.pi-offset:100j]
    x = rad * np.cos(theta)
    y = rad * np.sin(theta)
    z = 0. * rad
    line3 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=25, shade=False, lw=0.25,alpha=0.)

    rad, theta = np.mgrid[aringmin:aringmax:4j, 0.0-offset:1.0*np.pi-offset:100j]
    x = rad * np.cos(theta)
    y = rad * np.sin(theta)
    z = 0. * rad
    line4 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=25, shade=False, lw=0.25,alpha=0.)

    rad, theta = np.mgrid[fringmin:1.005*fringmin:2j, 0.0-offset:1.0*np.pi-offset:100j]
    x = rad * np.cos(theta)
    y = rad * np.sin(theta)
    z = 0. * rad
    line7 = ax3.plot_surface(x, y, z, color="w", edgecolor='b', rstride = 8, cstride=25, shade=False, lw=0.1,alpha=0.)

阴影：

def draw_shadowboundary(ax3, sundir):
    #azimuthal angle between x direction and direction of sun
    alpha = np.arctan2(sundir[1],sundir[0])
    #adjustments to keep -pi/2 < alpha < pi/2
    alphaadj = 0.*np.pi/180.
    if (alpha<0.):
        alpha += 2.*np.pi
    if ((alpha >= np.pi/2.) & (alpha <= np.pi)):
        alpha += np.pi
        alphaadj = np.pi
    if ((alpha > np.pi) & (alpha <= 3.*np.pi/2.)):
        alpha -= np.pi
        alphaadj = np.pi
    if (alpha>3.*np.pi/2.):
        alpha-=2*np.pi 

    #azimuthal angle between x direction and northern summer -- found using VIMS_2005_14_OMICET and VIMS_2017_053_ALPORI to define eq. of plane of Sun's annual path in chosen coordinate system: -0.193318*x + 0.1963755*y + 0.5471502*z = 0
    beta = 44.5505*np.pi/180.
    #Saturn's obliquity -- from NASA fact sheet
    psi = 26.73*np.pi/180.
    #Saturn's oblateness -- from NASA fact sheet
    obl = 0.09796
    #helpful definitions for optimization
    cpsic = np.cos(psi*np.cos(alpha+beta))
    spsic = np.sin(psi*np.cos(alpha+beta))
    calpha = np.cos(alpha)
    salpha = np.sin(alpha)
    #Saturn's projected shorter planetary axis as seen by the sun & ring inner edge
    req = 60268. / 1000.    
    b = req*sqrt((1.-obl)*(1.-obl)*cpsic*cpsic + spsic*spsic)
    ringstart = 1.239 * req
    ringend = 2.270 * req
    #shadow boundary of Saturn's rings -- can approximate using a=inf and cancelling terms
    a = 9.582*1.496*10.**5
    shadowline = lambda x,y : (1/a)*sqrt((req*salpha*(-a+x*calpha*cpsic+y*salpha)*(y*calpha-x*cpsic*salpha)/sqrt((y*calpha-x*cpsic*salpha)**2 + (x*spsic)**2) + calpha*(a*cpsic*(x*calpha*cpsic+y*salpha) + b*x*(a-x*calpha*cpsic-y*salpha)*spsic*spsic/sqrt((y*calpha-x*cpsic*salpha)**2 + (x*spsic)**2)))**2 + (req*calpha*(a-x*calpha*cpsic-y*salpha)*(y*calpha-x*cpsic*salpha)/sqrt((y*calpha-x*cpsic*salpha)**2 + (x*spsic)**2) + salpha*(a*cpsic*(x*calpha*cpsic+y*salpha)+b*x*(a-x*calpha*cpsic-y*salpha)*spsic*spsic/sqrt((y*calpha-x*cpsic*salpha)**2 + (x*spsic)**2)))**2)
    #azimuthal radius & antisolar angle for inequalities
    radius = lambda x,y : np.sqrt(x**2+y**2)
    anti = lambda x,y : abs(np.arctan2(y,x)-(alpha-alphaadj))

    #properties of shadow
    samples=1200
    d = np.linspace(-3*req,3*req,samples)
    x,y = np.meshgrid(d,d)
    #z = ((radius(x,y)<=shadowline(x,y)) & (ringstart<=radius(x,y)) & (np.pi/2<=anti(x,y)) & (anti(x,y)<=3.*np.pi/2)).astype(int)
    z = ((radius(x,y)<=shadowline(x,y)) & (ringstart<=radius(x,y)) & (radius(x,y)<=ringend) & (np.pi/2<=anti(x,y)) & (anti(x,y)<=3.*np.pi/2)).astype(int)
   cmap = matplotlib.colors.ListedColormap(["k","k"])
    #add shadow to plot
    ax3.contourf(x,y,z, [0.5,1.50001], cmap=cmap,alpha=0.5)

组合图形：

def plot_results(datafile, plot_names):
    plot_names.append("occultation_track_" + starname)
    fig2 = plt.figure(figsize=(9,9))
    ax3 = fig2.add_subplot(111, projection='3d')
    setup_saturn_plot(ax3, phi, theta, False, False, "star")
    draw_saturn(ax3, phi, theta)
    draw_rings(ax3, phi, theta, 'back')
    draw_rings(ax3, phi, theta, 'front')
    draw_shadowboundary(ax3,sundir)
    ax3.set_xlim([-200, 200]) 
    ax3.set_ylim([-200, 200])
    ax3.set_zlim([-200, 200])

代码产生如下图像：

该灰色阴影应该存在于地球前面的环上。但是，它不会显示在行星的前面，因此实际上只出现了行星右侧的一小部分阴影。阴影在所有情况下均能正确显示，除非需要在地球前方。

对此有任何解决办法吗？

Answer 1

目前，我正在努力弄清这段代码，但与此同时，至少到目前为止，这似乎是matplotlib3d的已知问题。

正如@TheImportanceOfBeingErnest很久以前指出的那样，此问题出现在mpl3d faq

中

我的3D图在某些视角下看起来不正确

这可能是mplot3d最常报告的问题。问题是-从某些角度看-3D对象会出现在另一个对象的前面，即使它实际上在后面。这可能会导致绘图看起来“物理上不正确”。

不幸的是，尽管为减少这种假象的发生而进行了一些工作，但这目前是一个棘手的问题，只有在matplotlib支持其核心的3D图形渲染之后才能完全解决。

由于将3D数据缩减为2D + z阶标量而出现问题。单个值表示集合中3D对象所有部分的三维尺寸。因此，当两个集合的边界框相交时，可能会出现此伪像。此外，两个3D对象（例如多边形或面片）的交集无法在matplotlib的2D渲染引擎中正确渲染。

在所有后端都添加了OpenGL支持之前，此问题可能无法解决（非常欢迎使用补丁程序）。在此之前，如果您需要复杂的3D场景，建议使用MayaVi。