Get Euler angles from gp_Trsf with gp_Quaternion::getEulerAngles()

Hi,

I am creating a transformation (rotation only) by rotating around three fixed axes X, Y, Z by three angles c, b, a. As the result I am getting a gp_Quaternion "q".

Now I want to extract three euler angles "aProbe, bProbe, cProbe" from "q" in order to create the same transformation again (rotate around fixed axes X, Y, Z with cProbe, bProbe, aProbe). This results in a second gp_Quaternion "qProbe".

After all the "q" and "aProbe" should be equal.

The question is: How do I extract "cProbe, bProbe, aProbe" from "q"? Or: what "gp_EulerSequence sequence" do I have to use?

I thought "Extrinsic = fixed Axes, XYZ = order of Axes" and tried these two possibilities:

q.GetEulerAngles(gp_Extrinsic_XYZ, cProbe, bProbe, aProbe);
q.GetEulerAngles(gp_Extrinsic_XYZ, aProbe, bProbe, cProbe);

But both fails (q != qProbe). :-(

Ok, I can try all possibilities, but I want to understand what I am doing.

Here is my sample code:
---snip---
const double TO_RAD = M_PI / 180.0;
const double TO_DEG = 1.0 / TO_RAD;

double a = 10.0 * TO_RAD; // degrees
double b = 20.0 * TO_RAD; // degrees
double c = 30.0 * TO_RAD; // degrees

// Calculate trsf from three angles a, b, c
gp_Trsf trsf1, trsf2, trsf3, trsf;
trsf1.SetRotation(gp::OX(), c); // rotate around fixed X-Axis with c
trsf2.SetRotation(gp::OY(), b); // rotate around fixed Y-Axis with b
trsf3.SetRotation(gp::OZ(), a); // rotate around fixed Z-Axis with a
trsf = trsf1 * trsf2 * trsf3;
gp_Quaternion q = trsf.GetRotation();

// Check angles
double aProbe, bProbe, cProbe;
q.GetEulerAngles(sequence, aProbe, bProbe, cProbe);
//
gp_Trsf trsf1Probe, trsf2Probe, trsf3Probe, trsfProbe;
trsf1Probe.SetRotation(gp::OX(), cProbe);
trsf2Probe.SetRotation(gp::OY(), bProbe);
trsf3Probe.SetRotation(gp::OZ(), aProbe);
trsfProbe = trsf1Probe * trsf2Probe * trsf3Probe;
gp_Quaternion qProbe = trsfProbe.GetRotation();
---snap---

Regards
Thorsten