Transcript MATLAB - University of Leeds

MATLAB
Graphics
Basic Plotting Commands
• figure
• plot(x)
: creates a new figure window
: 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 specified
in string : 'r' = red, 'g'=green, etc
for a limited set of basic colours.
'' solid line, ' ' dashed, 'o'
circles…see graphics section of
helpdesk
>> plot(glon,glat)
>> xlabel('Longitude'),ylabel('Latitude')
>> title('Flight Track : CW96 960607')
>>
>>
>>
>>
plot3(glon,glat,palt,'linewidth',2)
grid
xlabel('Longitude'),ylabel('Latitude')
zlabel('Altitude (m)')
Subplots
• subplot(m,n,p) : create a subplot in an array of axes
>> subplot(2,3,1);
P=1
P=2
P=3
>> subplot(2,3,4);
m
P=4
n
Contour plots
• contour(Z)
• contour(Z,n)
• contour(Z,v)
: plot contours of matrix Z
: plot n contours (n = integer)
: 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 C
and vector of handles to
to contours, h.
• contourf(Z)
• clabel(C,h)
• clabel(C,h,v)
: plot contours filled with
colour
: add labels to contours
: add labels only at
contours specified in v
• clabel(C,h,'manual')
: add labels to contours at
locations selected with
mouse
>> 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…
>> P = peaks;
>> contour(P)
>> contour(P,[-9:0.5:9])
>> [C,h]=contour(P);
>> clabel(C,h);
>> contourf(P,[-9:0.5:9]);
>> colorbar
Pseudocolour plots
An alternative to contouring – provides a
continuous 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
>> pcolor(P)
Data points are at vertices of grid,
colour of facet indicates mean value of
vertices. Colours are selected by
interpolating data range into a
colormap
>> shading flat
>> shading interp
>>
>>
>>
>>
>>
>>
pcolor(P);shading flat
hold on
contour(P,[1:9],'k')
contour(P,[-9:-1],'k--')
contour(P,[0 0],'k','linewidth',2)
colorbar
colormaps
• Surfaces are coloured by scaling the data range
to 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
>> colormap mapname
>> colormap('mapname')
• The current colormap can be retrieved with
>> map=colormap
>> colormap cool
>> caxis([0 8])
>> colorbar
• Colormaps are simply 3-column matrices of
arbitrary length (default = 64 rows). Each row
contains the [RED GREEN BLUE] components
of the colour required, specified on a 01 scale.
e.g.
>> mymap = [ 0
0
0.1
0
0.1 0.2
0.1 0.2 0.3
.
.
.
.
.
. ]
>> colormap(mymap)
Handle Graphics
• MATLAB uses a hierarchical graphics model
– Graphics objects organised according to their
dependencies: e.g. lines must be plotted on axes,
axes must 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
Object Hierarchy
root
figure
axes
line
UI-control
light
image
UI-menu
patch
UI-contextmenu
surface
rectangle
text
• Each graphics object has properties that can be
modified, e.g. for a line object: colour, width, line
style, marker style, stacking order on plot,…
• Many properties can be modified via the figure
window. Tools available depend upon the
version running – greatly expanded in version 7.
• More useful to use command line – much faster,
and can be included in scripts or functions to
automate whole process.
Object select
Add/edit text
Add arrow & line
zoom
3D rotate
• Properties of an object with handle H, can be
inspected/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 figure – returns handle of current figure
– gca : get current axes – returns handle of current axes
– gco : get current object – returns handle of current object
Can use these directly, instead of the handle
• 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.
dy
axis 'position' within the
figure: (default units are
'normalized')
dx
x0
y0
Figure's 'position' on screen is [x0 y0 dx dy]
(default units are pixels)
axis position within the
figure: it's 'position'
(default units are
'normalized')
Figure's default position on
the page: it's 'paperposition'
(default 'paperunits' are
'centimeters')
A4 page
Parameter value pairs
• Many basic plotting commands accept
parameter-value pairs to specify plotting
characteristics:
– plot(x,y,'para1',value1,'para2',value2,…)
• Commonly used parameters : values
– 'linewidth'
– 'color'
: in points, numeric (default =0.5)
: '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)
Adding Text to Figures
• Basic axis labels and title can be added via
convenient functions:
>> xlabel('x-axis label text')
>> ylabel('y-axis label text')
>> title('title text')
• Legends for line or symbol types are added via
the legend function:
>> legend('line 1 caption','line 2 caption',…)
>> legend([h1,h2,…],'caption 1','caption 2',…)
>>
>>
>>
>>
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)')
>>
>>
>>
>>
>>
>>
>>
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')
• 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 the
specified location (in data coordinates – locations
outside the current axes limits are OK)
>> gtext('text to add') – adds text at a location
selected with the cursor
Obtaining Values from a Figure
• The ginput function returns values from cursorselected points on a graph.
>> [x,y] = ginput(n)
>> [x,y] = ginput
– selects n values
– selects values until
'return' key is pressed
NB. ginput works on the current axes, and will return
values outside visible axis data range if points outside
axis frame are selected.
Printing Figures
• At its simplest, the command
>> print
sends the current figure to the default printer.
>> print –fn
prints figure number n to the default printer
• Under unix, a command line switch may be used
to specify a printer:
>> print –Pprinter
Printing to Files
• A wide variety of file formats are supported for
printing; the general form is:
>> print –driver –options filename
e.g.
>> print –dps filename
print postscript file
>> print –dpsc filename
print colour postscript file
>> print –depsc filename
print colour encapsulated postscript file
>> print –djpeg filename
print JPEG file (a BAD file format for
almost any figure)
>> print –dpng –r200 filename
print PNG file at 200dpi.
All bit-mapped file formats accept a –rnnn option
to specify print resolution (default is 150dpi)
.png
.jpg
Saving a MATLAB figure
• The functions hgsave and hgload save and
load a figure to a .fig file – this 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 the
figure are NOT saved.
>> hgsave(gcf,'filename')
>> hgload('filename.fig')
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.
>> load /cw96/jun07/jun07_all_5km_means.mat
>> who
Your variables are:
mQ
mlat
mlon
msst
mtheta
mws
mthetav
>> plot(mlon,mlat,'o')
>> print -dpng -r100 figures/grid-1-data-points
mu
mv
>>
>>
>>
>>
>>
>>
>>
[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
>>
>>
>>
>>
>>
gu=griddata(mlon,mlat,mu,XX,YY);
gv=griddata(mlon,mlat,mv,XX,YY);
quiver(XX,YY,gu,gv,'k-');
set(h1,'markeredgecolor','r','markersize',5)
print -dpng -r100 figures/grid-3-wind-field-and-vectors
>>
>>
>>
>>
>>
>>
>>
>>
>>
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
% 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=4:33
data1=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 to
hold 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 file
movie2avi(Qframes,'testavi.avi','compression','none')