19_sky_grid_sampling.cpp

Hemispherical altitude/azimuth sky-grid sampling.

// SPDX-License-Identifier: AGPL-3.0-or-later
// Copyright (C) 2026 Vallés Puig, Ramon

 
#include <cassert>
#include <cmath>
#include <iostream>
 
#include <siderust/siderust.hpp>
 
int main() {
  using namespace siderust;
 
  // Uniform 10° grid over the upper hemisphere: 9 alt rings × 36 az steps.
  auto uniform = SkyGrid::uniform(qtty::Degree(10.0));
  auto cells = uniform.cells();
  std::cout << "uniform 10deg grid: " << cells.size() << " cells\n";
  assert(cells.size() == static_cast<std::size_t>(9 * 36));
 
  // Equal-area grid: per-cell solid angles sum to the hemisphere (2pi sr).
  auto equal_area = SkyGrid::equal_area(qtty::Degree(5.0), qtty::Degree(5.0));
  double total_sr = 0.0;
  for (const auto &cell : equal_area.cells()) {
    total_sr += cell.solid_angle.value();
  }
  std::cout << "equal-area total solid angle: " << total_sr
            << " sr (hemisphere = " << 2.0 * constants::pi << " sr)\n";
  assert(std::abs(total_sr - 2.0 * constants::pi) / (2.0 * constants::pi) < 0.01);
 
  // Apply a 20deg horizon mask via the builder.
  auto masked = SkyGrid::with_steps(qtty::Degree(10.0), qtty::Degree(10.0));
  masked.with_alt_range(qtty::Degree(20.0), qtty::Degree(90.0));
  std::cout << "20deg horizon mask: " << masked.cells().size() << " cells\n";
  assert(masked.cells().size() < cells.size());
 
  std::cout << "SkyGrid sampling OK\n";
  return 0;
}