13 - matlab m_map地学绘图工具基础函数 - 介绍创建管理颜色映射的函数m_colmap和轮廓图绘制颜色条的函数m_contfbar

0. 引言

   本篇介绍下m_map中用于创建和管理颜色映射函数（m_colmap）和 为轮廓图绘制颜色条的函数（m_contfbar）。

1. 关于m_colmap

  m_colmap函数用于创建和管理颜色映射（colormap）。颜色映射可以用来对数据进行可视化编码，例如在地图上显示温度、高度、速度等信息。

m_colmap函数的一般形式如下：

cols=m_colmap(nme,m,ncol)
% m_colmap  Useful colormaps
%   m_colmap(NAME) returns an M-by-3 matrix containing the NAME colormap
%   where NAME is one of:
%     'jet' : a perceptually uniform variation of the JET colormap. It
%             contains the multiple colours which make JET useful, while
%             avoiding the weird highlighting especially around yellow and
%             cyan. The colors begin with dark blue, range through shades
%             of blue, green, orange and red, and ends with dark red.
%     'mBOD' : a modified blue/orange diverging colormap without white,
%              useful as a colorblind-friendly jet alternative
%
%     'diverging' : a blue/red diverging colormap
%     'BOD' : a blue/orange diverging colormap
%     'rBOD' : a different blue/orange colormap with gray in the middle
%
%     'odv'  : an isoluminant map 
%     'cyclic2': a cyclic colormap (for angles) with two dark regions
%     'cyclic1': a cyclic colormap (for angles) with one dark region
%
%     'land' : a topographic height (green-brown-white) shading
%     'water' : blue shading for water (goes with 'land').
%     'gland' : a topographic height  shading with more green
%     'bland' : a topographic height shading with browns only.
%
%     'blue' : a perceptually useful blue shading (good for bathymetry)
%     'green' : a perceptually useful green shading
%     'chlorophyll': Enhanced green for chlorophyll (to red)
%     'CBchlorophyll': Enhanced green for chlorophyll (to magenta)
%                               <-colorblind friendly
%
%     'EK80' : a standard echo-sounder map.
%     'chart':  the standard chart colour (single color)
%
%   and M is the same length as the current figure's colormap. If no
%   figure exists, the length of the default colormap is used. The
%   length can be explicitly specified with s_colmap(NAME,M).
%
%   m_colmap('demo') demonstrates the colormaps.
%
%   m_colmap(NAME,'step') returns a 256-color map in which colours are
%   perceptually bunched into 16 separate colours. This is useful
%   if you want to see "edges" in what would be an otherwise
%   smooth gradation (i.e. approaching the look of contouring).
%
%   m_colmap(NAME,'demo') Gives a demo of this behavior
%
%   m_colmap(NAME,'step',M) bunches into M colours.

  其中，nme 选择一种颜色类型；m 颜色长度，不设置就自动用默认的，设置了就颜色条按区间进行分段；

  m_map的所有颜色类型可以通过下面一句代码查看：

m_colmap demo

m_colmap函数的使用示例，示例数据可以从网盘获取，提取码：ofxi：

%% m_colormap
clc;clear;
ncFilePath = 'GLDAS_NOAH10_M.A200602.021.nc4';
lon = ncread(ncFilePath,'lon');
lat = ncread(ncFilePath,'lat');    
soilmoi_data = ncread(ncFilePath,'SoilMoi0_10cm_inst'); [LN,LT]=meshgrid(lon,lat);m_proj('mercator','long',[69.5 105.5],'lat',[24.5 40.5]);
% 在地图上绘制伪彩色图
m_pcolor(LN,LT, soilmoi_data');colormap( m_colmap('jet') );
%colormap( m_colmap('jet',10) );% 添加地图边界、标签和色标
m_gshhs('ic','color',[.5 .5 .5]) % 中等分辨率海岸线
m_gshhs('ir2','color','k')   % 中等分辨率河流
m_grid('linestyle','none','tickdir','out');
colorbar;

  对比下图可以发现，绘制在图右侧的颜色调划分上存在差异，这就是设置了m的差别，根据需要选择合适的命令参数，能够绘出更加符合的图示：

2. 关于m_contfbar

  m_contfbar函数用于添加色标，以显示地图上的等值线或填充的数据的颜色对应的数值范围。

  m_contfbar函数的一般形式是：

[ ax,h ] = m_contfbar(lon,lat,DATA,LEVELS)
% M_CONTFBAR Draws a colour bar for contourf plots 
%    M_CONTFBAR([X1,X2],Y,DATA,LEVELS) draws a horizontal colourbar
%    between the normalized coordinates (X1,Y) and (X2,Y) where
%    X/Y are both in the range 0 to 1 across the current axes.
%    Negative values can be used to position outside the axis.
%
%    Differences from COLORBAR are: the bar is divided into solid
%    colour patches exactly corresponding to levels provided by
%    CONTOURF(DATA,LEVELS) instead of showing the whole continuous
%    colourmap, the parent axis is not resized, the axis can be made
%    as large or small as desired, and the presence of values 
%    above/below contoured levels is indicated by triangular pieces
%    (MATLAB 2014b or later).
%
%    M_CONTFBAR(X,[Y1,Y2],...) draws a vertical colourbar
%
%    The DATA,LEVELS pair can also be replaced with CS,CH where
%    [CS,CH]=CONTOURF(DATA,LEVELS).
%
%    M_CONTFBAR(...,'parameter','value') lets you specify extra
%    parameter/value pairs for the colourbar in the usual handle-graphics
%    way. Parameters you might set include 'xticks','xticklabels',
%    'xscale','xaxisloc' (or corresponding y-axis parameters for
%    a vertical colourbar) and 'fontsize'.
%
%    Additional parameter/value pairs allow special customization of the
%    colourbar:
%        'axfrac' : width of the colourbar (default 0.03)
%        'endpiece' : 'yes' (default) or 'no' show triangular
%                      endpieces.
%        'levels' : 'set' (default) shows a colourbar with exactly
%                   the levels in the LEVELS argument. 
%                   'match' shows only the subsect of levels actually
%                   used in the CONTOURF call. E.g., if your data ranges
%                   from (say) 121 to 192, and LEVELS=[10:10:300],
%                   then only levels in 130:10:190 actually appear in both
%                   the CONTOURF and the colourbar.
%         'edgecolor' : 'none' removes edges between colors.
%
%    [AX,H]=M_CONTFBAR(...) returns the handle to the axis AX and to
%    the contourobject H. This is useful to add titles, xlabels, etc.
%
%    M_CONTFBAR(BAX,...) where BAX is an axis handle draws the colourbar
%    for that axis.

其中：

• lon,lat 控制色标的位置，([lon1 lon2],[lat]…)表示横向色标；([lon1],[lat1 lat2]…)纵向色标；
• DATA 进行绘图的输入数据；
• axfrac 设置色标宽度 设置value数值；
• endpiece 设置结束端，yes 或 no；
• edgecolor 色标框边缘颜色，可以设置’r’ 、'g’等matlab内置颜色，也可以设置none；

m_contfbar函数的使用示例(在官网示例上不断尝试修改）：

m_proj('lambert','lat',[5 24],'long',[105 125]);set(gcf,'color','w')   % Set background colour before m_image call
caxis([-6000 0]);
colormap(flipud([flipud(m_colmap('blues',10));m_colmap('jet',118)]));
m_etopo2('shadedrelief','gradient',3);
m_gshhs_i('patch',[.8 .8 .8]);
m_grid('box','fancy');
ax=m_contfbar(.97,[.5 .9],[-6000 0],[-6000:100:000],'edgecolor','none','endpiece','no','axfrac ',0.1);
xlabel(ax,'meters','color','k');

  示例运行结果，上边的可选参数可自行修改。

3. 结语

   本篇介绍了用于创建和管理颜色映射函数（m_colmap）和 为轮廓图绘制颜色条的函数（m_contfbar）,通过示例展示了各函数的基本用法，对于绘制常见地学图已经够用了，后面如果发现还有其它相关函数再进行补充。希望对绘图的你有所帮助

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