How can I select data in a pcolor plot by using a rectangle?

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James Foster
James Foster 2019-7-31
评论： KSSV 2019-8-2
I am working with netcdf data to display a weather radar file. I used the pcolor function pcolor(X,Y,C) to plot the matrix of X and Y with the matrix data in C. I converted the X and Y data to cartesian from polar to make it easier to select data. The X and Y in the figure are distance in km from the center of the radar site.
My issue arises where I need to select a smaller portion of the data and only use that for analysis. I want to select from a center point specified as X and Y from the figure and select data that is in a 5x5km box broken up into 4 quadrants around the center point that I have specified. I have tried creating 4 rectangles around the selected data, but I do not know how to tell matlab to display a pcolor image of only of those rectangles. Is there a way to tell matlab to use only what is inside the rectangles for analysis? I have posted my code below with the result. Thanks!
nc=netcdf.open('C:\Users\james\Desktop\Thesis\23May2011NetCDFs\Lowest Elevation\ncswp_RaXpol_20110523_232645.602_u17_s130_4.0_SUR_.nc','NC_NOWRITE');
ZC=netcdf.getVar(nc,netcdf.inqVarID(nc,'DBZ'));
ZCdouble = double(ZC);
Ind=find(ZCdouble>30000);
ZCdouble(Ind)=NaN;
Ind1=find(ZCdouble<=0);
ZCdouble(Ind1)=NaN;
ZCdouble=ZCdouble./100;
DRC=netcdf.getVar(nc,netcdf.inqVarID(nc,'ZDR'));
DRCdouble = double(DRC);
IndZ=find(DRCdouble>30000);
DRCdouble(IndZ)=NaN;
INDZDR=find(DRCdouble<=-1000);
DRCdouble(INDZDR)=NaN;
Ind7=find(DRCdouble>1000);
DRCdouble(Ind7)=NaN;
DRCdouble=DRCdouble./100;
el= netcdf.getVar(nc,netcdf.inqVarID(nc,'Elevation')); %Elevation angle (deg)
[dimname, num_gates] = netcdf.inqDim(nc,netcdf.inqDimID(nc,'maxCells')); %number of range gates, find from the maxcells var in 'dimensions' of ncdump
delr=netcdf.getVar(nc,netcdf.inqVarID(nc,'Cell_Spacing')); %space between gates (m)
r_min=netcdf.getVar(nc,netcdf.inqVarID(nc,'Range_to_First_Cell')); %Distance to first range gate (m)
az_set=netcdf.getVar(nc,netcdf.inqVarID(nc,'Azimuth'));
el_rad = el/180*pi;
az_rad = az_set/180*pi;
phi_ref=0;
[r,az_rad] = meshgrid(((0:num_gates-1)*delr+r_min)/1e3,az_rad);
x2 = r.*cos(el_rad).*sin(az_rad); %MATRIX DIMENSIONS MUST AGREE
y2 = r.*cos(el_rad).*cos(az_rad);
z2 = r.*sin(el_rad);
Range = r(1,:);
[YCart,XCart] = pol2cart(az_rad,Range);
%centerXY = centerdata;
% plot the power in dBZ with a map overlay
figure (1);
XCenter = -8.4281;
YCenter = 7.1656;
newX = XCart';
newY = YCart';
Zfig = pcolor(newX,newY,ZCdouble);
hold on
%Specify 4 rectangle positions from center
toprightZ=rectangle('Position',[XCenter YCenter 5.0000 5.0000]);
topleftZ=rectangle('Position',[XCenter-5 YCenter 5 5]);
bottomrightZ=rectangle('Position',[XCenter YCenter-5 5 5]);
bottomleftZ=rectangle('Position',[XCenter-5 YCenter-5 5 5]);
set(Zfig, 'ZData', get(Zfig,'CData')); %Makes the data values show up in the data cursor as Z
caxis([0 55])
shading flat
colorbar
xlabel('Zonal Distance (km)')
ylabel('Meridional Distance (km)')
title('Reflectivity Factor (dBZ)')
ZYdata=Zfig.YData;
ZXdata=Zfig.XData;
ZZdata=Zfig.ZData;

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回答（1 个）

KSSV
KSSV 2019-8-1
Read about interp2.
Fix your (Xi,Yi) for which you want to extract the data and use interp2. Something like below:
xi = linspace(xval0,yval1,m) ; % the value of x you want
yi = linspace(yval0,yval1,n) ; % the value of y you want
[Xi,Yi] = meshgrid(xi,yi) ;
Zi = interp2(X,Y,C,Xi,Yi) ;
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James Foster
James Foster 2019-8-2
I cannot post the data because it is privately owned. That is also the entire code that I am using. I am confused what the interp2 function does. What does it do exactly in the code you posted?
KSSV
KSSV 2019-8-2
[X,Y,Z] = peaks(100) ;
pcolor(X,Y,Z)
shading interp ; colorbar
% Say I want to pick data from (-2,-2) to (2,2)
[Xi,Yi] = meshgrid(-2:2,-2:2) ;
Zi = interp2(X,Y,Z,Xi,Yi) ;
figure
pcolor(Xi,Yi,Zi)
shading interp

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