geometry > 中心からの線と交わるstar shape(星形)のedgeを探す > find_rayCrossing_starShapedEged_180417 v0.1

```txt:動作環境
GeForce GTX 1070 (8GB)
ASRock Z170M Pro4S [Intel Z170chipset]
Ubuntu 16.04.4 LTS desktop amd64
TensorFlow v1.7.0
cuDNN v5.1 for Linux
CUDA v8.0
Python 3.5.2
IPython 6.0.0 -- An enhanced Interactive Python.
gcc (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609
GNU bash, version 4.3.48(1)-release (x86_64-pc-linux-gnu)
scipy v0.19.1
geopandas v0.3.0
MATLAB R2017b (Home Edition)
ADDA v.1.3b6
gnustep-gui-runtime v0.24.0-3.1
PyMieScatt v1.7.0
```

### 処理概要

- 星形の頂点座標が与えられる
    - 辺を取得
- 中心からrayを飛ばす
- rayと交差する辺を探す

### 使用モジュール

- geometry_starShaped_180415 v0.1
    - [geometry > numpy > star shaped (星形) の座標を得る | Matplotlibでの描画 > v0.3:座標は得られた | v0.4: モジュール化](https://qiita.com/7of9/items/e23c81db584ffae7edd3)
- geometry_lineintersect_180415 v0.2
    - [geometry > numpy > 二線分（有限長さ）の交差判定 > 無限長さの二線分の交点を使った判定](https://qiita.com/7of9/items/c4ade7dfa3f09cf1be49)

### code v0.1

Jupyter

```py:find_rayCrossing_starShapedEged_180417.ipynb
%matplotlib inline

import numpy as np
import matplotlib.pyplot as plt
from pylab import rcParams
from itertools import combinations
import geometry_starShaped_180415 as GSS
import geometry_lineintersect_180415 as GLI

'''
v0.1 Apr. 17
  - check the crossing
      + import [geometry_lineintersect_180415]
  - define the ray from the center
    + draw the ray
    + add [xs_ray], [ys_ray]
    + add [theta_deg]
  - add idxs_seq[], combs[]
  - import [combinations]
  - branched from [geometry_starShaped_180414.ipynb]
'''

rcParams['figure.figsize'] = 14, 7
rcParams['figure.dpi'] = 110

# 1. obtain star shaped points
RAD_INNER = 5
RAD_OUTER = 10
xs_str, ys_str = GSS.get_starShaped(RAD_INNER, RAD_OUTER)

# 2. obtain combinations of points
idxs_seq = range(len(xs_str))  # sequential indices to obtain combinations
combs = []  # combinations to obtain all the edges
for acomb in combinations(idxs_seq, 2):
    combs += [acomb]
print(combs)

# 3. define the ray from the center
theta_deg = 0.0  # [deg] 0 for rightward direction, 90 for downward direction
radius = RAD_OUTER * 1.1  # 1.1 to cross the outmost edge
xs_ray, ys_ray = [0.0], [0.0]  # center
xs_ray += [radius * np.cos(np.deg2rad(theta_deg))]  # outmost
ys_ray += [radius * np.sin(np.deg2rad(theta_deg))]  # outmost
print(xs_ray, ys_ray)

fig = plt.figure()

ax1 = fig.add_subplot(1, 2, 1)
ax1.scatter(xs_str, ys_str)
ax1.set_xlabel('x')
ax1.set_ylabel('y')
ax1.plot(xs_ray, ys_ray)
ax1.grid(True)

# 4. find crossing edges
a1 = np.array([xs_ray[0], ys_ray[0]])
a2 = np.array([xs_ray[1], ys_ray[1]])
for aidx in combs:
    print(aidx, end='')
    b1 = np.array([xs_str[aidx[0]], ys_str[aidx[0]]])
    b2 = np.array([xs_str[aidx[1]], ys_str[aidx[1]]])
    res = GLI.is_intersected(a1, a2, b1, b2)
    # print(res)
    #if res:
    #    ax1.plot(b1, b2)
    if res:
        xs_draw = [b1[0], b2[0]]
        ys_draw = [b1[1], b2[1]]
        ax1.plot(xs_draw, ys_draw)


fig.tight_layout()
```

### 実行

- 成功?: 交差する辺だけを拾っている
- 不具合: divide by zeroエラー発生
- 不具合: pentagonの辺まで見つかっている

![qiita.png](https://qiita-image-store.s3.amazonaws.com/0/32870/76b0a394-d2ba-4391-5952-0d4c753cb285.png)

### はまり

Matplotlibのplot()は(xs, ys)を渡す。(1つ目の点、２つ目の点)を間違って渡して3分ハマった。