Python自学笔记――Matplotlib风羽自定义

Python自学笔记——Matplotlib风羽自定义对于气象专业的小学生来说，风场是预报重要的参考数据，我们所知的风羽有四种：短线代表风速2m/s，长线代表风速4m/s，空心三角代表风速20m/s，实心三角代表风速50m/s。而matplotlib的风羽只有短线、长线、三角三种，而这里的三角不分空心实心，但是可通过改变风羽颜色为白色使三角变为空心形状，虽然这三种可以自定义各自代表的风速，但是仍与我们的使用习惯不符，即使把三角设成20m/s，原本一个实心三角就能表示的50m/s的风在matplotlib中需要两个三角外加两条长线一条短线。为了迎合预报员的需求，我在研究了matplotlib的风场函数barbs()的源代码quiver.py文件后，对quiver.py做了适当的调整，使得matplotlib也有了空心三角和实心三角之分。一、函数barbs的使用barb(X,Y,U,V,,**kw)X：风场数据X坐标Y：风场数据Y坐标U：风的水平方向分量V：风的垂直方向分量'''Demonstrationofwindbarbplots'''importmatplotlib.pyplotaspltimportnumpyasnpx=np.linspace(-5,5,5)X,Y=np.meshgrid(x,x)U,V=12*X,12*Ydata=[(-1.5,.5,-6,-6),(1,-1,-46,46),(-3,-1,11,-11),(1,1.5,80,80),(0.5,0.25,25,15),(-1.5,-0.5,-5,40)]data=np.array(data,dtype=[('x',np.float32),('y',np.float32),('u',np.float32),('v',np.float32)])#Defaultparameters,uniformgridax=plt.subplot(2,2,1)ax.barbs(X,Y,U,V)#Arbitrarysetofvectors,makethemlongerandchangethepivotpoint#(pointaroundwhichthey'rerotated)tobethemiddleax=plt.subplot(2,2,2)ax.barbs(data['x'],data['y'],data['u'],data['v'],length=8,pivot='middle')#Showingcolormappingwithuniformgrid.Fillthecircleforanemptybarb,#don'troundthevalues,andchangesomeofthesizeparametersax=plt.subplot(2,2,3)ax.barbs(X,Y,U,V,np.sqrt(U*U+V*V),fill_empty=True,rounding=False,sizes=dict(emptybarb=0.25,spacing=0.2,height=0.3))#Changecolorsaswellastheincrementsforpartsofthebarbsax=plt.subplot(2,2,4)ax.barbs(data['x'],data['y'],data['u'],data['v'],flagcolor='r',barbcolor=['b','g'],barb_increments=dict(half=10,full=20,flag=100),flip_barb=True)plt.show()二、源代码解读1.classBarbs()classBarbs(mcollections.PolyCollection):@docstring.interpddef__init__(self,ax,*args,**kw):'...'def_find_tails(self,mag,rounding=True,half=5,full=10,flag=50):'...'def_make_barbs(self,u,v,nflags,nbarbs,half_barb,empty_flag,length,pivot,sizes,fill_empty,flip):'...'defset_UVC(self,U,V,C=None):'...'defset_offsets(self,xy):'...'通过读源代码可知类Barbs有五个方法分别为__init__、_find_tails、_make_barbs、set_UVC、set_offsets。[e-mail]__init__(self,ax,*args,**kw):Theconstructortakesonerequiredargument,anAxesinstance,followedbytheargsandkwargsdescribedbythefollowingpylabinterfacedocumentation:%(barbs_doc)sself._pivot=kw.pop('pivot','tip')self._length=kw.pop('length',7)barbcolor=kw.pop('barbcolor',None)flagcolor=kw.pop('flagcolor',None)self.sizes=kw.pop('sizes',dict())self.fill_empty=kw.pop('fill_empty',False)self.barb_increments=kw.pop('barb_increments',dict())self.rounding=kw.pop('rounding',True)self.flip=kw.pop('flip_barb',False)transform=kw.pop('transform',ax.transData)#Flagcolorandandbarbcolorprovideconvenienceparametersfor#settingthefacecolorandedgecolor,respectively,ofthebarb#polygon.Wealsoworkheretomaketheflagthesamecolorasthe#restofthebarbbydefaultifNonein(barbcolor,flagcolor):kw['edgecolors']='face'ifflagcolor:kw['facecolors']=flagcolorelifbarbcolor:kw['facecolors']=barbcolorelse:#Settofacecolorpassedinordefaulttoblackkw.setdefault('facecolors','k')else:kw['edgecolors']=barbcolorkw['facecolors']=flagcolor#Parseoutthedataarraysfromthevariousconfigurationssupportedx,y,u,v,c=_parse_args(*args)self.x=xself.y=yxy=np.hstack((x[:,np.newaxis],y[:,np.newaxis]))#Makeacollectionbarb_size=self._length**2/4#Empiricallydeterminedmcollections.PolyCollection.__init__(self,[],(barb_size,),offsets=xy,transOffset=transform,**kw)self.set_transform(transforms.IdentityTransform())self.set_UVC(u,v,c)__init__()方法为初始化方法，此方法中flagcolor、barbcolor为设置风羽颜色的关键字，中间的说明文字提示颜色设置是针对所有的风羽的，所以通过颜色设置达不到风羽中既有空心白色三角又有实心黑色三角。初始化方法中在对一些参数进行了初始化赋值后执行了set_UVC()方法，所以我们顺着这个set_UVC()方法往下继续读。3.set_UVC()defset_UVC(self,U,V,C=None):self.u=ma.masked_invalid(U,copy=False).ravel()self.v=ma.masked_invalid(V,copy=False).ravel()ifCisnotNone:c=ma.masked_invalid(C,copy=False).ravel()x,y,u,v,c=delete_masked_points(self.x.ravel(),self.y.ravel(),self.u,self.v,c)else:x,y,u,v=delete_masked_points(self.x.ravel(),self.y.ravel(),self.u,self.v)magnitude=np.hypot(u,v)flags,emptyflags,barbs,halves,empty=self._find_tails(magnitude,self.rounding,**self.barb_increments)#Gettheverticesforeachofthebarbsplot_barbs=self._make_barbs(u,v,flags,emptyflags,barbs,halves,empty,self._length,self._pivot,self.sizes,self.fill_empty,self.flip)self.set_verts(plot_barbs)#SetthecolorarrayifCisnotNone:self.set_array(c)#Updatetheoffsetsincasethemaskeddatachangedxy=np.hstack((x[:,np.newaxis],y[:,np.newaxis]))self._offsets=xyself.stale=True在此方法中，首先进行了变量的命名赋值，然后依次执行了方法_find_tails和_make_barbs。_make_barbs的输入为_find_tails的输出，_find_tails的输入中有一个为magnitude=np.hypot(u,v)，np.hypot()为勾股定理方法，因此可知magnitude为风速。4._find_tailsdef_find_tails(self,mag,rounding=True,half=5,full=10,flag=50):'''Findhowmanyofeachofthetailpiecesisnecessary.Flagspecifiestheincrementforaflag,barbforafullbarb,andhalfforhalfabarb.Magshouldbethemagnitudeofavector(i.e.,=0).Thisreturnsatupleof:(*numberofflags*,*numberofbarbs*,*half_flag*,*empty_flag*)*half_flag*isabooleanwhetherhalfofabarbisneeded,sincethereshouldonlyeverbeonehalfonagivenbarb.*empty_flag*flagisanarrayofflagstoeasilytellifabarbisempty(toolowtoplotanybarbs/flags.'''#Ifrounding,