From f3cdb72c3b56ee5dc5019cdb9eef7fa91d6d6146 Mon Sep 17 00:00:00 2001
From: knodlseder <>
Date: Wed, 2 Feb 2011 13:31:48 +0000
Subject: [PATCH] initial version

---
 inst/cta/src/GCTASupport.cpp | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 inst/cta/src/GCTASupport.hpp | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 122 insertions(+), 0 deletions(-)
 create mode 100644 inst/cta/src/GCTASupport.cpp
 create mode 100644 inst/cta/src/GCTASupport.hpp

diff --git a/inst/cta/src/GCTASupport.cpp b/inst/cta/src/GCTASupport.cpp
new file mode 100644
index 0000000..709ea8f
--- /dev/null
+++ b/inst/cta/src/GCTASupport.cpp
@@ -0,0 +1,89 @@
+/***************************************************************************
+ *                 GCTASupport.cpp  -  CTA support functions               *
+ * ----------------------------------------------------------------------- *
+ *  copyright (C) 2011 by Jurgen Knodlseder                                *
+ * ----------------------------------------------------------------------- *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+/**
+ * @file GCTASupport.cpp
+ * @brief Implementation of support function used by CTA classes
+ * @author J. Knodlseder
+ */
+
+/* __ Includes ___________________________________________________________ */
+#ifdef HAVE_CONFIG_H
+#include <config.h>
+#endif
+#include "GCTASupport.hpp"
+#include "GTools.hpp"
+
+/* __ Coding definitions _________________________________________________ */
+
+
+/***********************************************************************//**
+ * @brief Returns length of circular arc within circular ROI
+ *
+ * @param[in] rad Circle radius in radians (<pi).
+ * @param[in] dist Circle centre distance to ROI centre (<pi).
+ * @param[in] cospsf Cosine of circle centre distance to ROI centre.
+ * @param[in] sindist Sinus of circle centre distance to ROI centre.
+ * @param[in] roi Radius of ROI in radians.
+ * @param[in] cosroi Cosine of ROI radius.
+ *
+ * This method returns the arclength in radians of a circle of radius 'rad'
+ * with a centre that is offset by 'dist' from the ROI centre, where the ROI
+ * radius is given by 'roi'. To speed-up computations, the cosines and sinus
+ * of 'roi' and 'psf' should be calculated by the client and be passed to
+ * the method.
+ ***************************************************************************/
+double cta_roi_arclength(const double& rad,     const double& dist,
+                         const double& cosdist, const double& sindist,
+                         const double& roi,     const double& cosroi)
+{
+    // Declare arclength
+    double arclength;
+
+    // Handle special case that circle centre matches ROI centre
+    if (dist == 0.0) {
+        if (rad > roi) arclength = 0.0;   // Circle outside ROI
+        else           arclength = twopi; // Circle inside ROI
+    }
+
+    // ... otherwise circle and ROI centres are not identical
+    else {
+
+        // Handle special case that we evaluate exactly at the circle
+        // centre. In this case we have in fact a point, and if this point
+        // falls within the ROI it has a formal arclength of 2pi.
+        //
+        if (rad == 0.0) {
+            if (dist > roi) arclength = 0.0;   // Circle centre outside ROI
+            else            arclength = twopi; // Circle centre inside ROI
+        }
+
+        // ... otherwise we have to handle the general case
+        else {
+            double dist = roi - dist;
+            if (-rad >= dist) 
+                arclength = 0.0;
+            else if (rad <= dist) 
+                arclength = twopi;
+            else {
+                double cosrad = cos(rad);
+                double sinrad = sin(rad);
+                double cosang = (cosroi - cosdist*cosrad) / (sindist*sinrad);
+                arclength = acos(cosang);
+            }
+        }
+
+    } // endelse: Circle and ROI centres were not identical
+
+    // Return arclength
+    return arclength;
+}
diff --git a/inst/cta/src/GCTASupport.hpp b/inst/cta/src/GCTASupport.hpp
new file mode 100644
index 0000000..8a5a8fb
--- /dev/null
+++ b/inst/cta/src/GCTASupport.hpp
@@ -0,0 +1,33 @@
+/***************************************************************************
+ *                 GCTASupport.hpp  -  CTA support functions               *
+ * ----------------------------------------------------------------------- *
+ *  copyright (C) 2011 by Jurgen Knodlseder                                *
+ * ----------------------------------------------------------------------- *
+ *                                                                         *
+ *   This program is free software; you can redistribute it and/or modify  *
+ *   it under the terms of the GNU General Public License as published by  *
+ *   the Free Software Foundation; either version 2 of the License, or     *
+ *   (at your option) any later version.                                   *
+ *                                                                         *
+ ***************************************************************************/
+/**
+ * @file GCTASupport.hpp
+ * @brief Definition of support function used by CTA classes
+ * @author J. Knodlseder
+ */
+
+#ifndef GCTASUPPORT_HPP
+#define GCTASUPPORT_HPP
+
+/* __ Includes ___________________________________________________________ */
+
+/* __ Namespaces _________________________________________________________ */
+
+/* __ Constants __________________________________________________________ */
+
+/* __ Prototypes _________________________________________________________ */
+double cta_roi_arclength(const double& rad,     const double& dist,
+                         const double& cosdist, const double& sindist,
+                         const double& roi,     const double& cosroi);
+
+#endif /* GCTASUPPORT_HPP */
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