Restricting a set of data by a spherical radius

Question

jgillis16 2015-8-3

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/232217-restricting-a-set-of-data-by-a-spherical-radius

编辑： jgillis16 2015-8-10

virgoclusterrm.txt

I need to restrict column 3 of the attached text file by a spherical radius with a central number of 12.51 that has a radius that extends 0.7333 in every direction.

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Walter Roberson 2015-8-3

What do you want to happen for cases that do not match that?

Is "dec" intended to convey "declination", and is "ra" intended to convey "right ascension" (instead of "radius" for example) ?

What formula should be used to test to see if a value is in range?

jgillis16 2015-8-4

在 MATLAB Online 中打开

I have some octave code as a reference... but I don't know how to implement it into matlab (but this code should take care of this problem)

function d=angulardist(ra1,dec1,ra2,dec2)
    error(mynargchk(4,4,nargin,"struct"));
    if common_size(ra1,dec1) && common_size(ra2,dec2)
      error("angulardist: input vector dimensions don't match");
    endif
    if !common_size(ra1,ra2)
      d=sind(dec1).*sind(dec2)+cosd(dec1).*cosd(dec2).*cosd(ra1-ra2);
    elseif columns(ra1)==1 && rows(ra2)==1
      d=sind(dec1)*sind(dec2)+(cosd(dec1)*cosd(dec2)).*cosd(repmat(ra1,1,length(ra2))-repmat(ra2,length(ra1),1));
    else
      error("angulardist: input vector dimensions don't match");
    endif
    idx=find(d>1+eps);
    d=real(acosd(d));
    if ~isempty(idx)
      warning("angulardist: irregular angular coordinates");
      d(idx)=nan;
    endif
endfunction
function out=selectobjectsinfield(in,RA,DEC,fieldDesc,rejectflag)
    error(mynargchk(4,5,nargin,"struct"));
    if nargin<5
      rejectflag=false;
    endif
    if isscalar(fieldDesc)
      circle=true;
      radius=fieldDesc;
    else
      circle=false; # rectangle
      RAwidth=fieldDesc(1);
      DECwidth=fieldDesc(2);
    endif
    ra=[in(:).RA];
    dec=[in(:).dec];
    if circle==true
      angularDist=angulardist(ra,dec,RA,DEC);
      if rejectflag
        idx=find((abs(angularDist)>=radius));
      else
        idx=find((abs(angularDist)<=radius));
      endif
    else
      RADist=angulardist(ra,dec,RA,dec);
      decDist=angulardist(ra,dec,ra,DEC); 
      if rejectflag
        idx=find((abs(RADist)>=RAwidth/2)&(abs(decDist)>=DECwidth/2));
      else
        idx=find((abs(RADist)<=RAwidth/2)&(abs(decDist)<=DECwidth/2));
      endif
    endif
    out=in(idx);
endfunction

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Answer 1

Walter Roberson 2015-8-4

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/232217-restricting-a-set-of-data-by-a-spherical-radius#answer_188128

在 MATLAB Online 中打开

function d=angulardist(ra1,dec1,ra2,dec2)
      if ~(isscalar(ra1) || isscalar(dec1) || isequal(size(ra1),size(dec1)) &&
         ~(isscalar(ra2) || isscalar(dec2) || isequal(size(ra2),size(dec2))
        error("angulardist: input vector dimensions don't match");
      end
      if ~(isscalar(ra1) || isscalar(ra2) || isequal(size(ra1),size(ra2))
        d = sind(dec1).*sind(dec2)+cosd(dec1).*cosd(dec2).*cosd(ra1-ra2);
      elseif size(ra1,2)==1 && size(ra2,1)==1
        d = sind(dec1)*sind(dec2)+(cosd(dec1)*cosd(dec2)).*cosd(repmat(ra1,1,length(ra2))-repmat(ra2,length(ra1),1));
      else
        error("angulardist: input vector dimensions don't match");
      end
      idx = find(d>1+eps);
      d = real(acosd(d));
      if ~isempty(idx)
        warning("angulardist: irregular angular coordinates");
        d(idx)=nan;
      end
end
function out = selectobjectsinfield(in,RA,DEC,fieldDesc,rejectflag)
      if nargin<5
        rejectflag=false;
      end
      if isscalar(fieldDesc)
        circle = true;
        radius = fieldDesc;
      else
        circle = false; # rectangle
        RAwidth = fieldDesc(1);
        DECwidth = fieldDesc(2);
      end
      ra = [in(:).RA];
      dec = [in(:).dec];
      if circle == true
        angularDist = angulardist(ra,dec,RA,DEC);
        if rejectflag
          idx = find((abs(angularDist)>=radius));
        else
          idx = find((abs(angularDist)<=radius));
        end
      else
        RADist = angulardist(ra,dec,RA,dec);
        decDist = angulardist(ra,dec,ra,DEC); 
        if rejectflag
          idx = find((abs(RADist)>=RAwidth/2)&(abs(decDist)>=DECwidth/2));
        else
          idx = find((abs(RADist)<=RAwidth/2)&(abs(decDist)<=DECwidth/2));
        end
      end
      out = in(idx);
end

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jgillis16 2015-8-4

在 MATLAB Online 中打开

Thanks! But, I come across an error

"Error: File: angular.m Line: 7 Column: 79
Expression or statement is incorrect--possibly unbalanced (, {, or [."

It's the first set of '&&' that is causing the issue.

Walter Roberson 2015-8-4

在 MATLAB Online 中打开

Change the first part to

      if ~(isscalar(ra1) || isscalar(dec1) || isequal(size(ra1),size(dec1))) &&
         ~(isscalar(ra2) || isscalar(dec2) || isequal(size(ra2),size(dec2)))
        error("angulardist: input vector dimensions don't match");
      end
      if ~(isscalar(ra1) || isscalar(ra2) || isequal(size(ra1),size(ra2)))