curve=BSplineCurve[{{198.2063059205538`,402.121623269958`},{191.2621031932776`,243.2810494404048`},{350.2070352491573`,246.3653323645185`},{307.7702781407043`,406.7480444184375`},{624.1169877141547`,382.0737810255268`},{367.1817351705904`,154.607913753287`},{408.0753377407309`,28.15231386462074`},{192.0336877673071`,89.837972346897`}},SplineDegree->3,SplineKnots->{0,0,0,0,1.`,2.`,3.`,4.`,5,5,5,5},SplineWeights->{1,1,1,1,1,1,1,1}];

cp = curve[[1]];
dg = curve[[2]] // Values;
kn = curve[[3]] // Values;
wg = curve[[4]] // Values;

x[t_]:=Total[Table[BSplineBasis[{dg,kn},j,t],{j,0,Length[kn]-dg-2}]*wg*cp[[All,1]]]/Table[BSplineBasis[{dg,kn},j,t],{j,0,Length[kn]-dg-2}].wg;
y[t_]:=Total[Table[BSplineBasis[{dg,kn},j,t],{j,0,Length[kn]-dg-2}]*wg*cp[[All,2]]]/Table[BSplineBasis[{dg,kn},j,t],{j,0,Length[kn]-dg-2}].wg;
f[t_]:=Sqrt[(x'[t])^2+(y'[t])^2];

FunctionInterpolation[zzz[t],{t,Min[kn],Max[kn]}]//Plot[#[g]-zzz[g],{g,Min[kn],Max[kn]},PlotRange->Full]&