Python 三维轴上填充等高线图中的瑕疵

我有一个令人沮丧的问题，只有在三维轴上绘制填充等高线图时，并且只有在某些情况下才会表现出来

下面是我遇到的问题的一个例子：

及

这些是不同等高线间隔的相同数据。 您会注意到在域的左侧出现了错误填充。这是一个通过打印命令将Z点压缩到Z=0平面的打印，如

ax3d.contourf(X, Y, dbz[z25,:,:], zdir='z', offset=0, levels=levels, cmap='pymeteo_radar', alpha=0.50)

无论使用的是alpha级别还是colormap，错误巡更都会发生，但对级别数很敏感。使用

zdir

和

offset

不会影响错误的轮廓（伪影只发生在Z表面上。如果我不填充轮廓，就不会出现错误的轮廓。我也可以改变域，有时会使问题变得更好（或更糟），但我在同一域中有许多图要绘制，因此这不是修复方法

在二维轴上绘制相同数据时，不会出现此问题，例如：

此图上有一些额外的数据，但您可以看到，填充的轮廓没有与在3d轴上发生的错误填充轮廓相同的伪影

下面是一个脚本，您可以运行它来重现问题

#!/usr/bin/env python
import numpy as np
import matplotlib.pyplot as plt
import mpl_toolkits.mplot3d.axes3d as p3

data=np.array([[53.9751,  51.5681,  50.7119,  51.1049,  51.5339,  51.4977,  51.2387,50.761,  50.1732,  49.8218,  49.5442,  48.936,  47.4498,  46.6484, 45.8542,  45.136,  44.5268,  44.071,  43.7665,  43.5928,  43.5269, 43.5385,  43.6053,  45.565,  47.0071,  46.8664,  47.372,  47.8324, 48.295,  48.731,  49.0522,  49.4001,  49.7111,  49.9919,  50.2527, 50.4928,  50.7135,  50.8831,  51.0806,  51.2683 ],
               [55.6671,  52.53,  50.7764,  50.5632,  51.2095,  51.5659,  51.521,  51.2143,  50.653,  50.2371,  49.989,  49.8089,  49.6058,  47.8355, 47.3124,  46.7346,  46.1616,  45.6498,  45.2462,  44.967,  44.8005, 44.7284,  44.7295,  44.7869,  46.959,  45.0194,  46.73,  48.0766, 48.9395,  49.5325,  49.8498,  50.1887,  50.4798,  50.7406,  50.9808, 51.2003,  51.4074,  51.555,  51.7429,  51.9218 ],
               [56.6513,  53.5919,  51.2774,  50.3133,  50.7705,  51.533,  51.8287, 51.7083,  51.2816,  50.7933,  50.4806,  50.2671,  50.1009,  50.0096, 49.9052,  49.4698,  47.4655,  47.0717,  46.6849,  46.3583,  46.1122, 45.952,  45.8678,  45.8485,  45.8811,  45.956,  46.0634,  47.2225, 49.4363,  50.2482,  50.527,  50.8558,  51.1358,  51.3809,  51.607, 51.8179,  52.0161,  52.1454,  52.3263,  52.497 ],
               [57.078,  54.3224,  52.0759,  50.4679,  50.4677,  51.297,  52.0284, 52.1594,  51.9395,  51.5518,  51.1419,  50.8765,  50.6686,  50.5101, 50.4078,  50.3473,  50.3592,  50.3813,  49.7504,  47.55,  47.324, 47.1365,  46.9978,  46.9119,  46.8743,  46.8811,  46.9257,  47.0013, 50.0148,  50.9106,  51.1133,  51.4282,  51.7064,  51.943,  52.1587, 52.3597,  52.4789,  52.6631,  52.8359,  52.9966 ],
               [57.3835,  54.9025,  52.8571,  50.9842,  50.5197,  51.1494,  52.0599, 52.4732,  52.4716,  52.2656,  51.9535,  51.6068,  51.3466,  51.1513, 50.9708,  50.8321,  50.7639,  50.7944,  50.8817,  49.8122,  48.2038, 48.086,  47.9704,  47.8735,  47.8035,  47.7644,  47.7574,  47.7803, 50.8194,  51.5486,  51.6645,  51.9745,  52.2349,  52.4508,  52.6481, 52.8317,  52.9412,  53.1097,  53.2699,  53.4171 ],
               [57.9157,  55.6092,  53.6306,  51.8011,  50.9372,  51.2615,  52.1406, 52.7436,  52.8528,  52.7829,  52.6322,  52.403,  52.1149,  51.866, 51.6624,  51.4773,  51.317,  51.2183,  51.2153,  51.1367,  48.5913, 48.6216,  48.6218,  48.5951,  48.5589,  48.527,  48.5081,  50.5185, 51.6998,  51.905,  52.2258,  52.4891,  52.7062,  52.8926,  53.0655, 53.2251,  53.3262,  53.4755,  53.6169,  53.7471 ],
               [58.6093,  56.432,  54.307,  52.6277,  51.584,  51.6482,  52.3762, 53.0685,  53.2545,  53.217,  53.1356,  53.0351,  52.8481,  52.6154, 52.39,  52.177,  51.9977,  51.843,  51.7172,  51.4587,  48.7481,  48.7984, 48.864,  48.9291,  48.9843,  49.0228,  50.496,  51.8667,  52.3404, 52.4759,  52.6889,  52.8851,  53.0525,  53.2072,  53.354,  53.4576, 53.5925,  53.7217,  53.8432,  53.956 ],
               [58.9719,  56.9885,  54.8768,  53.3526,  52.3025,  52.2089,  52.7762, 53.4444,  53.6768,  53.6706,  53.5692,  53.5162,  53.4373,  53.2886, 53.1113,  52.9065,  52.6988,  52.5193,  52.3544,  52.0384,  48.9624, 48.9653,  49.0005,  49.0574,  49.1258,  50.692,  51.9726,  52.4309, 52.699,  52.8194,  52.9845,  53.1336,  53.2669,  53.393,  53.5118, 53.6086,  53.7213,  53.8293,  53.9308,  54.026 ],
              [58.5754,  56.945,  55.068,  53.7798,  52.9469,  52.854,  53.3136,53.8929,  54.1205,  54.1178,  54.0128,  53.9289,  53.8906,  53.8239,53.717,  53.5724,  53.3818,  53.1892,  53.009,  49.3078,  49.2524,49.2165,  49.2032,  49.2187,  50.463,  51.9497,  52.4487,  52.7041,52.8358,  52.9776,  53.1101,  53.2293,  53.3419,  53.4487,  53.5401,53.6365,  53.7301,  53.8205,  53.9062,  53.9869 ],
              [57.623,  56.547,  55.0117,  54.0512,  53.5372,  53.5246,  53.927,54.3868,  54.5828,  54.5811,  54.4501,  54.3235,  54.2626,  54.2334,54.1802,  54.1137,  53.9897,  53.8202,  49.796,  49.6864,  49.5946,49.5216,  49.4703,  49.4432,  51.8479,  52.5574,  52.8359,  52.9722,53.0827,  53.1826,  53.2747,  53.3597,  53.4405,  53.5138,  53.5944,53.6751,  53.7536,  53.829,  53.9019,  53.9721 ],
              [56.902,  56.0005,  54.9159,  54.3352,  54.123,  54.2014,  54.5659,54.8917,  55.0307,  55.0139,  54.8838,  54.7044,  54.5863,  54.5548,54.5258,  54.4957,  54.4633,  51.4821,  50.1897,  50.0758,  49.9683,49.8704,  49.7842,  51.5064,  52.7625,  53.0724,  53.1926,  53.2682,53.3404,  53.4119,  53.4831,  53.5517,  53.6169,  53.6763,  53.7383,53.8009,  53.8644,  53.9281,  53.9905,  54.0517 ],
              [56.3455,  55.5524,  54.9336,  54.6836,  54.703,  54.8657,  55.1749,55.3844,  55.4521,  55.4019,  55.2622,  55.0281,  54.8981,  54.6591,54.7866,  54.7678,  54.7654,  54.0436,  54.2302,  52.2533,  50.3305,50.2276,  50.1268,  52.9617,  53.4395,  53.5504,  53.5481,  53.5524,53.5699,  53.6014,  53.644,  53.6931,  53.7445,  53.7996,  53.8548,53.9097,  53.9655,  54.0229,  54.0813,  54.1393 ],
              [55.7493,  55.3019,  55.1012,  55.0906,  55.234,  55.4751,  55.7134,55.8462,  55.8461,  55.7425,  55.5725,  55.3535,  55.1612,  54.958,55.0193,  54.9584,  54.9531,  54.8886,  54.8256,  54.2211,  50.6477,50.5564,  53.0546,  53.8592,  54.08,  54.0288,  53.9509,  53.8796,53.8307,  53.8073,  53.8034,  53.8142,  53.8383,  53.8725,  53.9128,53.9558,  54.0013,  54.0497,  54.103,  54.1597 ],
              [55.2575,  55.1664,  55.3165,  55.5004,  55.7345,  55.9901,  56.1852,56.2599,  56.2027,  56.0454,  55.818,  55.5754,  55.302,  55.2083,55.0224,  55.1415,  55.0656,  55.0446,  55.0263,  54.7728,  50.8924,53.4671,  54.2587,  54.5146,  54.6171,  54.519,  54.3857,  54.2497,54.1355,  54.0509,  53.9932,  53.9584,  53.941,  53.939,  53.9527,53.9798,  54.0111,  54.0465,  54.0868,  54.1339 ],
              [54.8665,  55.1533,  55.5095,  55.8512,  56.1541,  56.3995,  56.5593,56.6009,  56.5079,  56.3001,  56.0178,  55.7187,  55.448,  55.063,55.2016,  55.2116,  55.1817,  55.112,  55.1099,  55.0299,  54.3358,54.6966,  54.9199,  55.0156,  55.0728,  54.975,  54.8299,  54.6609,54.493,  54.3475,  54.2349,  54.1517,  54.0928,  54.0516,  54.0245,54.013,  54.0206,  54.0404,  54.0667,  54.0989 ],
              [54.2676,  55.1132,  55.6112,  56.09,  56.428,  56.6661,  56.8056,56.8374,  56.7339,  56.4923,  56.1474,  55.7977,  55.4805,  55.2341,54.8999,  55.2662,  55.2927,  55.185,  55.1237,  55.1268,  54.9772,55.1418,  55.2612,  55.3333,  55.379,  55.3244,  55.2153,  55.0629,54.881,  54.6926,  54.523,  54.3866,  54.2855,  54.2118,  54.1583,54.1191,  54.0935,  54.0834,  54.0885,  54.1057 ],
              [54.1771,  55.0795,  55.7075,  56.1772,  56.5183,  56.7522,  56.8898,56.9315,  56.8427,  56.6056,  56.2317,  55.8095,  55.4436,  55.183,55.0284,  54.9504,  55.2833,  55.2563,  55.1498,  55.1342,  55.1331,55.259,  55.3705,  55.4452,  55.4955,  55.5087,  55.4697,  55.3766,55.2324,  55.049,  54.8485,  54.6578,  54.4995,  54.3822,  54.3002,54.2427,  54.2022,  54.1749,  54.1598,  54.1561 ],
              [53.9112,  54.85,  55.6641,  56.0844,  56.4062,  56.6232,  56.757,56.8149,  56.7669,  56.5754,  56.2311,  55.785,  55.366,  55.0104,54.812,  54.8845,  55.1273,  55.2339,  55.1976,  55.1049,  55.0913,55.1843,  55.3048,  55.4076,  55.4709,  55.518,  55.5455,  55.5329,55.4636,  55.3349,  55.1595,  54.9529,  54.7462,  54.5681,  54.4342,54.3439,  54.2848,  54.2446,  54.2222,  54.2135 ],
              [53.9368,  54.9196,  55.4408,  55.7999,  56.0652,  56.2423,  56.348,56.4106,  56.4114,  56.3028,  56.0519,  55.6779,  55.2493,  54.8836,54.6592,  54.6347,  54.8341,  55.0606,  55.1396,  55.0967,  55.0325,55.0501,  55.1451,  55.2627,  55.3559,  55.4216,  55.4789,  55.5183,55.5245,  55.4779,  55.3701,  55.2072,  55.0029,  54.7876,  54.5915,54.4378,  54.3368,  54.2787,  54.2415,  54.2271 ],
              [53.9325,  54.6506,  55.0421,  55.2926,  55.4603,  55.5679,  55.6285,55.6792,  55.7234,  55.731,  55.639,  55.3923,  55.043,  54.6845,54.4188,  54.3242,  54.4606,  54.7449,  54.9548,  55.0171,  55.0047,54.9454,  54.9666,  55.0651,  55.1828,  55.2677,  55.3308,  55.3914,55.438,  55.4544,  55.4277,  55.3385,  55.1907,  54.9981,  54.7786,54.5691,  54.4013,  54.2898,  54.233,  54.1994 ] ])

fig = plt.figure()
ax = fig.add_subplot(111,projection='3d')
X,Y = np.meshgrid(np.arange(-30.0,-20.0,0.25), np.arange(20.0,25,0.25))
ax.contourf(X,Y,data,zdir='z',offset=0, levels=np.arange(0,75,1))
ax.set_zlim(0.0,2.0)
plt.savefig('testfig.png')
plt.close()

此代码将生成以下绘图：

在所有情况下，我都观察到这种错误的等高线，坏三角形总是在域的左下角附近有一个顶点。我的数据是有规律的网格化的，并且所讨论的域在X和Y上是一致的。在这种情况下，如果等高线级别的数量减少，错误填充将消失。在其他一些情况下，这并不总是有帮助或者只是改变错误的视觉外观。在任何情况下，即使在非常粗糙的轮廓，我仍然会在我的图的子集中得到错误

以前有人看到过这一点并找到了解决方案吗？我忽略了什么吗？我愿意接受不涉及降低轮廓级别的解决方案（这确实减少了总体错误）。如果其他人一致认为这可能是mplot3d中的错误，我将向他们提交错误报告（）我感觉问题在于当

levels

选项导致密集轮廓时，绘制非常强的梯度轮廓，但奇怪的是，仅在3d轴上

相关版本信息：

• Python 3.4.1
• matplotlib 1.4.3
• numpy 1.9.0

---

问题很可能出在matplotlib本身，您没有做错任何事情
通过一点实验，我发现如果将输入数据乘以

1.01

或

0.999

，绘图结果会正确，但

1.001

或

0.9999

不足以解决问题
加上或减去常数会改变颜色，但会使问题变得明显
作为一种胡乱猜测，一些内部计算陷入了奇点（即使我无法想象在这种情况下什么公式会有危险）
你应该向他们的追踪者提交一个bug
编辑 再想一想，matplotlib可能正在尝试计算等高线多边形，而不是在逐像素的基础上计算背景纹理，这可能会导致恼人的精度问题，这取决于该值。绘制等高线更容易，因为您可以只使用行进方法计算线段不必担心重建完整的等高线拓扑（例如，如果等高线图中缺少一个非常小的线段，您无论如何都不会注意到）

---

如果这确实是错误，那么修复可能并不容易，因为需要以完全不同的方式重新实现平面图（即使更容易）路径。
这是matplotlib.mplot3d中的一个长期缺陷，在获取二维轮廓集并将其扩展到三维时忽略路径信息。这会导致在某些情况下，当打算作为“移动”的路径段被“绘制”时，带孔的路径渲染不正确
对于matplotlib的此问题，matplotlib 1.5.0稳定版修复了此错误
与问题中相同的测试代码使用matplotlib 1.5生成正确的绘图，如下所示：

---

事实证明，这是mplot3d中的一个缺陷，没有从2d轮廓中继承路径信息（代码只调用2d轮廓并添加z信息）。对于某些有孔的多边形，路径信息的丢失（例如移动，而不是绘制）导致多边形生成不好。我找到了一个适合当前主控形状的旧PR，并解决了问题。一旦它通过测试，我将把它提交回matplotlib。感谢反馈。@casey:哦，他们走了一条艰难的道路。我一直认为，如果只创建纹理而不是创建多边形，事情会简单得多是的，你需要能够处理至少有多个洞的多边形，这意味着你通常还需要低层的桥接计算逻辑，因为许多图形库不能正确处理洞。