Restricting a set of data by a spherical radius

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.

[James Tursa]

File is not attached.

[jgillis16]

Whoops! Attached now. Thanks!

[Walter Roberson]

Is the idea to replace the larger radius with the fixed value 0.7333, or do other values on in the same row need to be changed when the radius input is larger, or should rows with larger values be removed from the matrix?

[jgillis16]

Excuse me on the wording. We are concentrating on a central value of 12.51 in column 3 and that possesses a radius of 0.7333. So every number within that error range should be in column 3 (or at least in a variable).

[Walter Roberson]

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]

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

Answer 1

[Walter Roberson]

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

[jgillis16]

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]

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)))