Rotate to LQT


Wish this message finds you very well.

I am using obspy to rotate waveforms from (Z,N,E) to (P, SV, SH) via obspy function

l, q, t = obspy.rotate.rotate_zne_lqt(z, n, e, 83, -60).

83 is the angle between vector pointing from station to source and vector pointing from station to geographic north. Back-azimuth.

-60 is the angle measured up from horizontal; between a vector from station to projection of source point into xy plane and vector from station to source.

Apparently the function will raise an error since negative inclination is not allowed. according to the function the allowed range for the inclination is (0,360) exclusive.

According to my understating the inclination if measured from horizontal should have range from (-90 to 90) and if measured down from straight up should have range of (0, 180). For the later case the angle of -60 will be 90-60.

Would someone please inform me what reference the function is using for inclination.

My sincere regards


Hi Khalil,

we use these definitions:

The incidence is the angle from vertical down at which an incoming ray arrives, so reasonable values are 0 to 180 degree (0 to 90 if the station is at the surface of the Earth). Incidence angles larger than 180 degree mean that the backazimuth has to be interpreted in a different way for the L and Q components. For the T component it does not change.

I also realized that we currently do not specify the definition of the incidence angle so I opened an issue:

Please feel free to tackle it.



Thank you very much,

Well clarified, my appreciations