MATLAB (2): Graphics

8/12/2019 MATLAB (2): Graphics

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MATLABGraphics


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Basic Plotting Commands

figure : creates a new figure windowplot(x) : plots line graph of x vs index

number of array

plot(x,y) : plots line graph of x vs y

plot(x,y,'r--'): plots x vs y with linetype specifiedin string : 'r' = red, 'g'=green, etc

for a limited set of basic colours.

'' solid line, '' dashed, 'o'circlessee graphics section ofhelpdesk


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>> plot(glon,glat)>> xlabel('Longitude'),ylabel('Latitude')>> title('Flight Track : CW96 960607')


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>> plot3(glon,glat,palt,'linewidth',2)>> grid>> xlabel('Longitude'),ylabel('Latitude')>> zlabel('Altitude (m)')


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Subplots

subplot(m,n,p): create a subplot in an array of axes

>> subplot(2,3,1);

>> subplot(2,3,4);

m

n

P=1 P=2 P=3

P=4


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Contour plots

contour(Z) : plot contours of matrix Z contour(Z,n) : plot n contours (n = integer)

contour(Z,v) : plot contours at levels

specified in vector v

contour(X,Y,Z): plot contours of matrix Z on

grid specified by X and Y

[C,h]=contour(): returns contour matrix Cand vector of handles to

to contours, h.


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contourf(Z) : plot contours filled withcolour

clabel(C,h) : add labels to contours

clabel(C,h,v) : add labels only atcontours specified in v

clabel(C,h,'manual')

: add labels to contours atlocations selected with

mouse


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>> peaks;

Peaks is an example function, useful for demonstrating 3D

data, contouring, etc. Figure above is its default output.

P=peaks;- return data matrix for replotting


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>> P = peaks;>> contour(P)


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>> contour(P,[-9:0.5:9])


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>> contourf(P,[-9:0.5:9]);>> colorbar


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Pseudocolour plots

An alternative to contouringprovides acontinuous colour-mapped 2D data field

pcolor(Z) : plot pseudocolour plot of Z

pcolor(X,Y,Z) : plot of Z on grid X,Y

shading faceted| flat| interp: set shading option

faceted : show edge lines (default)

flat : don't show edge lines interp : colour is linearly interpolated to give smooth

variation


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>> pcolor(P) >> shading flat

>> shading interpData points are at vertices of grid,

colour of facet indicates mean value of

vertices. Colours are selected by

interpolating data range into acolormap


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>> pcolor(P);shading flat>> hold on>> contour(P,[1:9],'k')>> contour(P,[-9:-1],'k--')

>> contour(P,[0 0],'k','linewidth',2)>> colorbar


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colormaps

Surfaces are coloured by scaling the data rangeto the current colormap. A colormap applies to

a whole figure.

Several predefined colormaps exist ('jet' (the

default), 'warm','cool','copper','bone','hsv').Select one with

>> colormapmapname

>> colormap('mapname') The current colormap can be retrieved with

>> map=colormap


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>> colormap cool


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>> caxis([0 8])>> colorbar


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Handle Graphics

MATLAB uses a hierarchical graphics model Graphics objects organised according to theirdependencies: e.g. linesmust be plotted on axes,

axesmust be positioned on figures

Every object has a unique identifier, or handle Handles are returned by creating function ax(n)=subplot(3,2,n)

h=plot(x,y)

Handles can be used to identify an object in order to inspect(get) or modify (set) its properties at any time


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root

figure

axes UI-control UI-menu UI-contextmenu

line light image patch surface rectangle text

Object Hierarchy


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Each graphics object has properties that can bemodified, e.g. for a line object: colour, width, linestyle, marker style, stacking order on plot,

Many properties can be modified via the figurewindow. Tools available depend upon theversion runninggreatly expanded in version 7.

More useful to use command linemuch faster,and can be included in scripts or functions toautomate whole process.


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Object selectAdd/edit text

Add arrow & linezoom

3D rotate


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Properties of an object with handle H, can beinspected/modified by:>> value = get(H,'propertyname')

>> set(H,'propertyname',value)

All property values echoed to screen by:>> get(H)

3 useful functions: gcf: get current figurereturns handle of current figure

gca: get current axesreturns handle of current axes

gco: get current objectreturns handle of current object

Can use these directly, instead of the handle


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Current object is last created (usually), or last object

clicked on with mouse.

>> pp = get(gca,'position')pp =

0.1300 0.1100 0.7750 0.8150

>> set(gca,'position',pp+[0 0.1 0 -0.1])

The code above first gets the position of the current axes location of bottom

left corner (x0, y0), width (dx) and height (dy) (in normalised units)then

resets the position so that the axes sit 0.1 units higher on the page and

decreases their height by 0.1 units.


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x0

y0

dx

dy

Figure's 'position' on screen is [x0y0dx dy]

(default units are pixels)

axis 'position' within thefigure: (default units are

'normalized')


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A4 page

Figure's default position on

the page: it's 'paperposition'

(default 'paperunits' are'centimeters')

axis position within the

figure: it's 'position'

(default units are'normalized')


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Parameter value pairs

Many basic plotting commands accept

parameter-value pairs to specify plottingcharacteristics:

plot(x,y,'para1',value1,'para2',value2,)

Commonly used parameters : values 'linewidth' : in points, numeric (default =0.5)

'color' : 'r','g','b','c','k','m','y'basic colours (strings)

: [R,G,B]red, green, blue components.

Range from 0 to 1 (0 to 100%), eg [0,0.5,1]

'marker' : shape of marker/symbol to plot'.' point, 'v' triangle, '^' triangle(up pointing),

'markeredgecolor','markerfacecolor'

: edge and body colours of plotting symbols

'markersize' : marker size in points (default = 6)


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Adding Text to Figures

Basic axis labels and title can be added viaconvenient functions:>> xlabel('x-axis label text')

>> ylabel('y-axis label text')

>> title('title text')

Legends for line or symbol types are added via

the legendfunction:>> legend('line 1 caption','line 2 caption',)

>> legend([h1,h2,],'caption 1','caption 2',)


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>> subplot(1,2,1)>> plot(theta(eval(sw1_2)),palt(eval(sw1_2)),'r');hold on>> plot(theta(eval(sw1_7)),palt(eval(sw1_7)),'g')>> xlabel('\theta (K)'); ylabel('Altitude (m)')


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>> hh(1)=plot(xwsc(eval(sw1_2)),palt(eval(sw1_2)),'r');>> hold on>> hh(2)=plot(xwsc(eval(sw1_7)),palt(eval(sw1_7)),'g');>> hh(3)=plot(xwsc(eval(sw1_5)),palt(eval(sw1_5)),'b');

>> xlabel('windspeed (m s^{-1})');>> set(gca,'yticklabel',[])>> legend(hh([1 3 2]),'sw2','sw5','sw7')


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MATLAB uses a subset of TEX commands for

mathematical symbols, greek characters etc.

Text may be added at any location via the

commands:

>> text(x,y,'text to add')adds text at thespecified location (in data coordinateslocations

outside the current axes limits are OK)

>> gtext('text to add')adds text at a location

selected with the cursor


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Obtaining Values from a Figure

The ginputfunction returns values from cursor-

selected points on a graph.

>> [x,y] = ginput(n) selects n values

>> [x,y] = ginput selects values until

'return' key is pressed

NB. ginputworks on the current axes, and will return

values outside visible axis data range if points outside

axis frame are selected.


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Printing Figures

At its simplest, the command

>> print

sends the current figure to the default printer.

>> print fn

prints figure number nto the default printer

Under unix, a command line switch may be used

to specify a printer:

>> print Pprinter


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.png .jpg


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Saving a MATLAB figure

The functions hgsaveand hgloadsave and

load a figure to a .figfilethis contains the

complete MATLAb handle graphics description

of the figure, which can then be modified at a

later date. NB the variables used to create thefigure are NOT saved.

>> hgsave(gcf,'filename')

>> hgload('filename.fig')


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Putting it all together

The following slides show the development of a

moderately complex figure from raw data :

near-surface aircraft measurements of basic

meteorology averaged down to 5km intervals

along the flight legs.


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>> load /cw96/jun07/jun07_all_5km_means.mat>> whoYour variables are:mQ mlat mlon msst mtheta mthetav mu mvmws

>> plot(mlon,mlat,'o')>> print -dpng -r100 figures/grid-1-data-points


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>> [XX,YY]=meshgrid([-125.2:0.05:-124],[39.9:0.05:40.8]);>> gmws=griddata(mlon,mlat,mws,XX,YY);>> pcolor(XX,YY,gmws); shading flat;>> hbar=colorbar;>> hold on>> h1=plot(mlon,mlat,'ko');>> print -dpng -r100 figures/grid-2-wind-field


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( 2 )


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>> set(gca,'linewidth',2,'fontweight','bold')>> xlabel('Longitude'); ylabel('latitude')>> set(hbar,'linewidth',2,'fontweight','bold')>> set(get(hbar,'xlabel'),'string','(m s^{-1})','fontweight','bold')>> xlabel('Longitude'); ylabel('latitude')>> title('CW96 : June 07 : 30m wind field')

>> load mendocinopatch.mat>> patch(mendocinopatch(:,1),mendocinopatch(:,2),[0.9 0.9 0.9])>> print -dpng -r100 figures/grid-4-wind-field-and-vectors-and-coast


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% generate movie frames from LEM fields

[XX,ZZ]=meshgrid(X,Z(iz));[YY,ZZ]=meshgrid(Y*0,Z(iz));ZH=ones([102 102])*Z(3);

for n=4:33data1=Q012D_K3{n};data2=Q012D_I50{n}(iz,:);surf(X,Y,ZH,data1);shading flat;set(gca,'xticklabel',{},'yticklabel',{},'zticklabel',{});set(gca,'xlim',[min(X) max(X)],'ylim',[min(Y) max(Y)])hold on

surf(XX,YY,ZZ,data2);shading flat;set(gca,'zlim',[0 max(Z(iz))])Qframes(n-3)=getframe; % NB first n=4, force frames index tohold off % start at 1 to avoid empty frames

End

% play movie in matlab

axis([0 1 0 1 0 1])set(gca,'visible','off')movie(Qframes,5)

% save movie to AVI filemovie2avi(Qframes,'testavi.avi','compression','none')


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MATLAB (2): Graphics