Changeset 9422 for trunk/MagicSoft/Mars/mcorsika

Timestamp:

04/16/09 10:46:32 (16 years ago)

Author:

tbretz

Message:

*** empty log message ***

File:

• trunk/MagicSoft/Mars/mcorsika/MCorsikaEvtHeader.cc (modified) (1 diff)

trunk/MagicSoft/Mars/mcorsika/MCorsikaEvtHeader.cc

@@ -61 +61 @@
 // --------------------------------------------------------------------------
 //
-//  Return Hypot(x, y)
+// Return Impact (distance of ground incident point from telescope axis)
+//
+// Distance d between a point q and a line u (via p):
+//   d = | ( vec(q) - vec(p) ) x vec(u) |  /  | vec(u) |
+//
+// If p = 0
+//
+//   ==>   d = | vec(q) x vec(u) |  /  | vec(u) |
+//          w :=  q = (x/y/0)
+//          v :=  u = (Alt/Az)
+//
+// For Alt/Az = Theta/Phi:
+//
+//  x = r sin(theta) cos(phi)
+//  y = r sin(theta) sin(phi)
+//  z = r cos(theta)
+//
+//                   (   -q3*u2    )   ( -cos(theta)*y                                     )
+// vec(q) x vec(u) = (    q3*u1    ) = (  cos(theta)*x                                     )
+//                   ( q1*u2-q2*u1 )   ( sin(theta) cos(phi) * y - sin(theta) sin(phi) * x )
+//
+//   ==> d = sqrt( cos(theta)^2 (x^2  + y^2 ) +
+//                 sin(theta)^2 ( cos(phi) y + sin(phi) x)^2 )
 //
 Double_t MCorsikaEvtHeader::GetImpact() const
 {
-    return TMath::Hypot(fX, fY);
+    const Double_t c = TMath::Cos(fZd);
+    const Double_t s = TMath::Sin(fZd);
+
+    const Double_t p = TMath::Cos(fAz)*fX - TMath::Sin(fAz)*fY;
+
+    return TMath::Sqrt(c*c*(fX*fX + fY*fY) + s*s* p*p);
 }