matplotlib删除地图投影上的等值线及风场.doc

matplotlib删除地图投影上的等值线及风场【前言】最近在编写一个气象应用程序，用来显示某一时刻某一地区的气温等值线和风场，程序主要用到了第三方库matplotlib及Basemap。在编写的过程中发现，如果不进行擦除操作直接绘制新的等值线或风场，新的等值线（风场）会与原来的等值线（风场）叠加在一起，而绘制的等值线及风场没有单独的remove方法，所以如果想要擦除已经绘制的等值线就要将地图重新投影一遍，如果地图投影精度高一点，整个投影过程就会特别漫长。通过对等值线及风场的返回结果进行研究，我找到了一个不必重新投影地图就可将等值线及风场擦除的方法。一、matplotlib及Basemapmatplotlib是Python常用的数据绘制包。它基于numpy的数组运算功能，可以轻易的画出各种统计图形，如散点图，条行图，饼图，等值线图等。Basemap是Matplotlib的一个子包，负责地图绘制。在数据可视化过程中，我们可以将数据在地图上画出来。利用matplotlib及Basemap画图的基本步骤是：1. 创建一个figure实例2. 在figure里创建Axes容器实例3. 在Axes容器内创建Basemap实例进行地图投影4. 调用Basemap实例的contour及barbs方法进行在地图上绘图二、不进行擦除操作直接绘制新的等值线或风场效果演示为了方便演示，数据为我自己手中的数据，其中values,x1,y1为等值线的数据及坐标，huvalues,hvvalues,x2,y2为风场的数据及坐标，数据的格式及获得方法就不做过多解释1. 绘制地图投影import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)plt.show()我们将得到下图演示的结果2. 绘制等值线import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)c= m.contour(x1,y1,values,15,linewidths=1.5)plt.show()得到结果如下：3. 继续绘制风场import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)c= m.contour(x1,y1,values,15,linewidths=1.5)b= m.barbs(x2,y2,huvalues*2.5,hvvalues*2.5)plt.show()得到结果如下：由此我们可以看出，如果在绘制新的等值线或者风场前不进行擦除操作，所有的图像都会叠加在一起三、通过重新进行地图投影进行擦除操作1. 绘制地图投影import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)plt.show()我们将得到下图演示的结果2. 绘制等值线import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)c= m.contour(x1,y1,values,15,linewidths=1.5)plt.show()得到结果如下：3. 擦除axes重新进行地图投影import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)x1,y1=m(lon,lat)c= m.contour(x1,y1,values,15,linewidths=1.5)ax.clear()m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)plt.show()得到下图结果：4. 绘制风场import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)c= m.contour(x1,y1,values,15,linewidths=1.5)ax.clear()m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)x2,y2= m(hulon,hulat)b= m.barbs(x2,y2,huvalues*2.5,hvvalues*2.5)plt.show()得到结果如下：此方法虽然可以达到预期的效果，但是我们的地图投影并未做过改变，重新进行地图投影毫无意义，而且还会占用系统不必要的资源四、对等值线实例及风场实例进行研究1. 等值线通过dir()命令我们可以查看创建的等值线实例c的属性方法print(dir(c)_A, _class_, _delattr_, _dict_, _dir_, _doc_, _eq_, _format_, _ge_, _getattribute_, _getstate_, _gt_, _hash_, _init_, _le_, _lt_, _module_, _ne_, _new_, _reduce_, _reduce_ex_, _repr_, _setattr_, _sizeof_, _str_, _subclasshook_, _weakref_, _add_label, _auto, _autolev, _check_xyz, _contour_args, _contour_generator, _contour_level_args, _corner_mask, _get_allsegs_and_allkinds, _get_label_clabeltext, _get_label_text, _get_lowers_and_uppers, _initialize_x_y, _levels, _make_paths, _process__args, _process_colors, _process_levels, _process_linestyles, _process_linewidths, _transform, add_checker, add_label, add_label_clabeltext, add_label_near, allkinds, allsegs, alpha, antialiased, autoscale, autoscale_None, ax, calc_label_rot_and_inline, callbacksSM, changed, check_update, clabel, cmap,collections, colorbar, colors, contour_doc, cvalues, extend, extent, filled, find_nearest_contour, get_alpha, get_array, get_clim, get_cmap, get_label_coords, get_label_width, get_real_label_width, get_text, get_transform, hatches, labelCValues, labelTexts, labels, layers, legend_elements, levels, linestyles, linewidths, locate_label, locator, logscale, monochrome, nchunk, norm, origin, pop_label, print_label, set_alpha, set_array, set_clim, set_cmap, set_label_props, set_norm, tcolors, tlinewidths, to_rgba, too_close, update_dict, vmax, vmin, zmax, zmin通过查看，发现在c的属性方法中并没有remove()方法，但是我们发现有一个属性是collections，这里的collections如果与Python的集合类相同，它就应该有remove()方法进删除，所以继续通过dir()命令进行查看print(dir(c.collections)_add_, _class_, _contains_, _delattr_, _delitem_, _dict_, _dir_, _doc_, _eq_, _format_, _ge_, _getattribute_, _getitem_, _getstate_, _gt_, _hash_, _iadd_, _imul_, _init_, _iter_, _le_, _len_, _lt_, _module_, _mul_, _ne_, _new_, _reduce_, _reduce_ex_, _repr_, _reversed_, _rmul_, _setattr_, _setitem_, _setstate_, _sizeof_, _str_, __,_subclasshook_, _weakref_, append, clear, copy, count, extend, index, insert, pop, remove, reverse, sort, type通过查看，发现c.collections有remove()方法，所以尝试用c.collections.remove()进行删除，由于remove()方法一次只能删除一个元素，所以要用for循环来进行删除。import matplotlib.pyplot as pltfrom mpl_toolkits.basemap import Basemapfig = plt.figure()ax = fig.add_axes(0,0,1,1)m = Basemap(projection= laea, lon_0= 90, lat_0= 40, width= 11000000, height= 8000000,resolution=l,ax=ax)m.drawcoastlines(color=tan)c= m.contour(x1,y1,values,15,linewidths=1.5)for i in c.collections: i.remove()plt.show()得到下图结果：由此可见，此方法可行2. 风场通过dir()命令我们可以查看创建的等值线实例b的属性方法print(dir(b)_add_, _class_, _contains_, _delattr_, _dir_, _doc_, _eq_, _format_, _ge_, _getattribute_, _getitem_, _getnewargs_, _gt_, _hash_, _init_, _iter_, _le_, _len_, _lt_, _mul_, _ne_, _new_, _reduce_, _reduce_ex_, _repr_, _rmul_, _setattr_, _sizeof_, _str_, _subclasshook_, count, index可以发现风场的实例b没有remove方法，也没有collections属性，所以决定先通过type()方法看看风场实例是什么类型的print(type(b)可以发现风场实例b是一个元组，所以继续看它的元素有什么属性print(dir(b0)_A, _class_, _delattr_, _dict_, _dir_, _doc_, _eq_, _format_, _ge_, _getattribute_, _getstate_, _gt_, _hash_, _init_, _le_, _lt_, _module_, _ne_, _new_, _reduce_, _reduce_ex_, _repr_, _setattr_, _sizeof_, _str_, _subclasshook_, _weakref_, _agg_filter, _alpha, _animated, _antialiaseds, _axes, _clipon, _clippath, _contains, _edgecolors, _edgecolors_original, _facecolors, _facecolors_original, _factor, _find_tails, _get_bool, _get_value, _gid, _hatch, _is_filled, _is_stroked, _label, _length, _linestyles, _linewidths, _make_barbs, _mouseover, _offset_position, _offsets, _oid, _path_effects, _paths, _picker, _pickradius, _pivot, _prepare_points, _propobservers, _rasterized, _remove_method, _set_gc_clip, _sizes, _sketch, _snap, _stale, _transOffset, _transform, _transformSet, _transforms, _uniform_offsets, _url, _urls, _visible, add_callback, add_checker, aname, autoscale, autoscale_None, axes, barb_increments, barbs_doc, callbacksSM, changed, check_update, clipbox, cmap, colorbar, contains, convert_xunits, convert_yunits, draw, eventson, figure, fill_empty, findobj, flip, format_cursor_data, get_agg_filter, get_alpha, get_animated, get_array, get_axes, get_children, get_clim, get_clip_box, get_clip_on, get_clip_path, get_cmap, get_contains, get_cursor_data, get_dashes, get_datalim, get_edgecolor, get_edgecolors, get_facecolor, get_facecolors, get_figure, get_fill, get_gid, get_hatch, get_label, get_linestyle, get_linestyles, get_linewidth, get_linewidths, get_offset_position, get_offset_transform, get_offsets, get_path_effects, get_paths, get_picker, get_pickradius, get_rasterized, get_sizes, get_sketch_params, get_snap, get_transform, get_transformed_clip_path_and_affine, get_transforms, get_url, get_urls, get_visible, get_window_extent, get_zorder, have_units, hitlist, is_figure_set, is_transform_set, mouseover, norm, pchanged, pick, pickable, properties, remove, remove_callback, rounding, set, set_UVC, set_agg_filter, set_alpha, set_animated, set_antialiased, set_antialiaseds, set_array, set_axes, set_clim, set_clip_box, set_clip_on, set_clip_path, set_cmap, set_color, set_contains, set_dashes, set_edgecolor, set_edgecolors, set_facecolor, set_facecolors, set_figure, set_gid, set_hatch, set_label,