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diff --git a/src/main.cc b/src/main.cc
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+// Copyright 2021, 2022 Benjamin Barenblat
+//
+// Licensed under the Apache License, Version 2.0 (the "License"); you may not
+// use this file except in compliance with the License. You may obtain a copy of
+// the License at
+//
+//     https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+// License for the specific language governing permissions and limitations under
+// the License.
+
+#include <getopt.h>
+#include <locale.h>
+
+#include <iostream>
+
+#include "src/glplanet.h"
+#include "src/x/init.h"
+#include "third_party/abseil/absl/strings/numbers.h"
+#include "third_party/abseil/absl/strings/string_view.h"
+
+namespace {
+
+constexpr absl::string_view kShortUsage = "Usage: glplanet [OPTION...]\n";
+
+constexpr absl::string_view kHelp = R"(
+Render a 3D globe lit in real time.
+
+Options:
+      --help                  display this help and exit
+      --longitude=DEGREES     center globe on this longitude, in degrees east
+      --latitude=DEGREES      center globe on this latitude, in degrees north
+      --version               display version and license information, and exit
+)";
+
+constexpr absl::string_view kAskForHelp =
+    "Try 'glplanet --help' for more information.\n";
+
+constexpr absl::string_view kVersionInfo = R"(glplanet development build
+Copyright 2021, 2022 Benjamin Barenblat
+Licensed under the Apache License, Version 2.0
+
+glplanet incorporates Eigen, whose source is governed by the terms of the
+Mozilla Public License, Version 2.0. Eigen's source is available at
+https://deb.debian.org/debian/pool/main/e/eigen3/eigen3_3.3.9.orig.tar.bz2.
+)";
+
+enum {
+  kHelpLongOption = 128,
+  kLongitudeLongOption,
+  kLatitudeLongOption,
+  kVersionLongOption,
+};
+
+}  // namespace
+
+int main(int argc, char* argv[]) {
+  setlocale(LC_ALL, "");
+  x::Initialize();
+
+  glplanet::MainOptions glplanet_options;
+
+  static option long_options[] = {
+      {"help", no_argument, nullptr, kHelpLongOption},
+      {"longitude", required_argument, nullptr, kLongitudeLongOption},
+      {"latitude", required_argument, nullptr, kLatitudeLongOption},
+      {"version", no_argument, nullptr, kVersionLongOption},
+      {nullptr, 0, nullptr, 0},
+  };
+  while (true) {
+    int c = getopt_long(argc, argv, "", long_options, /*longindex=*/nullptr);
+    if (c == -1) {
+      break;
+    }
+    switch (c) {
+      case kLongitudeLongOption:
+        if (!absl::SimpleAtod(optarg, &glplanet_options.longitude_degrees)) {
+          std::cerr << "glplanet: invalid longitude " << optarg << '\n';
+          return 1;
+        }
+        break;
+
+      case kLatitudeLongOption:
+        if (!absl::SimpleAtod(optarg, &glplanet_options.latitude_degrees)) {
+          std::cerr << "glplanet: invalid latitude " << optarg << '\n';
+          return 1;
+        }
+        break;
+
+      case kHelpLongOption:
+        std::cout << kShortUsage << kHelp;
+        return 0;
+      case kVersionLongOption:
+        std::cout << kVersionInfo;
+        return 0;
+      case '?':
+        std::cerr << kAskForHelp;
+        return 1;
+      default:
+        std::cerr << "Internal error; please report.\n";
+        return 1;
+    }
+  }
+  if (optind != argc) {
+    std::cerr << kShortUsage << kAskForHelp;
+    return 1;
+  }
+
+  return glplanet::Main(glplanet_options);
+}