[R] intercept point coordinates

[Tonja Krueger]

Hi List,
Can someone help me to calculate the coordinates of the red and green points? In this
example I found their approximate location by trying, but as I have to analyse
many similar curves, I’d rather calculate the exact location. 

data<-
c(0.008248005, 0.061242387, 0.099095516, 0.189943027, 0.227796157, 0.258078661,
0.280790538, 0.303502416, 0.386779301, 0.454914934, 0.545762445, 0.591186201,
0.682033712, 0.757739971, 0.825875604, 0.848587482, 0.803163726, 0.833446230,
0.878869985, 0.871299359, 0.878869985, 0.947005619, 1.000000000, 0.992429374,
0.954576245, 0.894011237, 0.765310597, 0.621468704, 0.492768064, 0.333784920,
0.258078661, 0.174801775, 0.099095516, 0.008248005)

plot(data, type="l")
abline(h=0.9)

points(21.35,.9, pch=20, col="red")
points(26,.9, pch=20, col="green")
 

Thank you, 
Tonja
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