"generate and export the data of a semicircle with chosen radius"
SetDirectory[NotebookDirectory[]];
R=1.2489;h=0.34;k=-1.2;
x[t_]:=R*Cos[t]+h;y[t_]:=R*Sin[t]+k;
datasemicircle=Table[{x[t],y[t]},{t,0.15Pi,0.58Pi,0.025Pi}];
lp=ListPlot[datasemicircle,PlotLabel->"{h,k}="<>ToString[{h,"k"}]<>"; R="<>ToString[R]];
pp=ParametricPlot[{x[t],y[t]},{t,0,Pi}];
lphk=ListPlot[{{h,k}},PlotMarkers->"O",PlotRange->{{-(h+R),(h+R)},{-(k-R),(k+R)}}];
Show[{lp,lphk,pp}]
(*Export["datasemicircle.dat",datasemicircle];*)
Export["datasemicircle_A4.dat",datasemicircle];

"Can you make the cirle to look really circular? To this end, you have to assure that the axes are of the same scale. Use AspectRatio->1 in ListPlot"
lp=ListPlot[datasemicircle,AspectRatio->1];
Show[pp,lp]

"Check whether the files is in your current Directory[]"
Directory[]
FileNames[]
FileExistsQ["datasemicircle.dat"]

"Now, import the file and name it 'rawdata' "
rawdata=Import["datasemicircle.dat"];
rawdata

ListPlot[rawdata]