Swap arguments phi, alpha in Pixel c'tor (#821)

This resolves #821 (closed).

Base/Axis/Pixel.cpp

@@ -16,11 +16,11 @@
 #include "Base/Axis/Bin.h"
 #include "Base/Vector/GisasDirection.h"
 
-Pixel::Pixel(const Bin1D& alpha_bin, const Bin1D& phi_bin)
-    : m_alpha(alpha_bin.lowerBound())
-    , m_phi(phi_bin.lowerBound())
-    , m_dalpha(alpha_bin.binSize())
+Pixel::Pixel(const Bin1D& phi_bin, const Bin1D& alpha_bin)
+    : m_phi(phi_bin.lowerBound())
+    , m_alpha(alpha_bin.lowerBound())
     , m_dphi(phi_bin.binSize())
+    , m_dalpha(alpha_bin.binSize())
 {
     auto solid_angle_value = std::abs(m_dphi * (std::sin(m_alpha + m_dalpha) - std::sin(m_alpha)));
     m_solid_angle = solid_angle_value <= 0.0 ? 1.0 : solid_angle_value;
@@ -35,7 +35,7 @@ Pixel* Pixel::createZeroSizePixel(double x, double y) const
 {
     const double phi = m_phi + x * m_dphi;
     const double alpha = m_alpha + y * m_dalpha;
-    return new Pixel(Bin1D::At(alpha), Bin1D::At(phi));
+    return new Pixel(Bin1D::At(phi), Bin1D::At(alpha));
 }
 
 R3 Pixel::getK(double x, double y, double wavelength) const