【WP7】判断GPS坐标是否在中国

由于某些原因，国内地图总会有些偏移。虽说这是个相对偏移，但总会对需要坐标定位的应用造成几百米的漂移。若定位坐标在国外，则不会存在此问题。因此我们需要判别当前坐标是否在国内，然后决定是否进行坐标修正。

判定坐标是否在国内，有下列几种方法可选：

通过网络地图接口查询
根据国家行政边界判定
根据国家行政边界近似判定

方法1，通过网络地图接口查询

网络接口：http://maps.google.com/maps/api/geocode/xml?latlng=xxx,xxx&sensor=false，其中latlng参数填写的是坐标的经纬度参数。

例如进行如下调用：http://maps.google.com/maps/api/geocode/xml?latlng=39.829632,117.059326&sensor=false

返回结果如下：

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

<?xml version="1.0" encoding="UTF-8"?>
<GeocodeResponse>
 <status>OK</status>
 <result>
  <type>route</type>
  <formatted_address>274 Provincial Rd, Sanhe, Langfang, Hebei, China</formatted_address>
  <address_component>
   <long_name>274 Provincial Rd</long_name>
   <short_name>S274</short_name>
   <type>route</type>
  </address_component>
  <address_component>
   <long_name>Sanhe</long_name>
   <short_name>Sanhe</short_name>
   <type>sublocality</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>Langfang</long_name>
   <short_name>Langfang</short_name>
   <type>locality</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>Hebei</long_name>
   <short_name>Hebei</short_name>
   <type>administrative_area_level_1</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>China</long_name>
   <short_name>CN</short_name>
   <type>country</type>
   <type>political</type>
  </address_component>
  <geometry>
   <location>
    <lat>39.8483120</lat>
    <lng>117.0741900</lng>
   </location>
   <location_type>APPROXIMATE</location_type>
   <viewport>
    <southwest>
     <lat>39.8292258</lat>
     <lng>117.0728091</lng>
    </southwest>
    <northeast>
     <lat>39.8674069</lat>
     <lng>117.0757736</lng>
    </northeast>
   </viewport>
   <bounds>
    <southwest>
     <lat>39.8292258</lat>
     <lng>117.0728091</lng>
    </southwest>
    <northeast>
     <lat>39.8674069</lat>
     <lng>117.0757736</lng>
    </northeast>
   </bounds>
  </geometry>
 </result>
 <result>
  <type>sublocality</type>
  <type>political</type>
  <formatted_address>Sanhe, Langfang, Hebei, China</formatted_address>
  <address_component>
   <long_name>Sanhe</long_name>
   <short_name>Sanhe</short_name>
   <type>sublocality</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>Langfang</long_name>
   <short_name>Langfang</short_name>
   <type>locality</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>Hebei</long_name>
   <short_name>Hebei</short_name>
   <type>administrative_area_level_1</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>China</long_name>
   <short_name>CN</short_name>
   <type>country</type>
   <type>political</type>
  </address_component>
  <geometry>
   <location>
    <lat>39.9827180</lat>
    <lng>117.0782950</lng>
   </location>
   <location_type>APPROXIMATE</location_type>
   <viewport>
    <southwest>
     <lat>39.8081545</lat>
     <lng>116.7572022</lng>
    </southwest>
    <northeast>
     <lat>40.0850111</lat>
     <lng>117.2599867</lng>
    </northeast>
   </viewport>
   <bounds>
    <southwest>
     <lat>39.8081545</lat>
     <lng>116.7572022</lng>
    </southwest>
    <northeast>
     <lat>40.0850111</lat>
     <lng>117.2599867</lng>
    </northeast>
   </bounds>
  </geometry>
 </result>
 <result>
  <type>locality</type>
  <type>political</type>
  <formatted_address>Langfang, Hebei, China</formatted_address>
  <address_component>
   <long_name>Langfang</long_name>
   <short_name>Langfang</short_name>
   <type>locality</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>Hebei</long_name>
   <short_name>Hebei</short_name>
   <type>administrative_area_level_1</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>China</long_name>
   <short_name>CN</short_name>
   <type>country</type>
   <type>political</type>
  </address_component>
  <geometry>
   <location>
    <lat>39.5380470</lat>
    <lng>116.6837520</lng>
   </location>
   <location_type>APPROXIMATE</location_type>
   <viewport>
    <southwest>
     <lat>39.4355307</lat>
     <lng>116.5841675</lng>
    </southwest>
    <northeast>
     <lat>39.6029123</lat>
     <lng>116.8444061</lng>
    </northeast>
   </viewport>
   <bounds>
    <southwest>
     <lat>38.4703170</lat>
     <lng>116.1166769</lng>
    </southwest>
    <northeast>
     <lat>40.0850111</lat>
     <lng>117.2599867</lng>
    </northeast>
   </bounds>
  </geometry>
 </result>
 <result>
  <type>administrative_area_level_1</type>
  <type>political</type>
  <formatted_address>Hebei, China</formatted_address>
  <address_component>
   <long_name>Hebei</long_name>
   <short_name>Hebei</short_name>
   <type>administrative_area_level_1</type>
   <type>political</type>
  </address_component>
  <address_component>
   <long_name>China</long_name>
   <short_name>CN</short_name>
   <type>country</type>
   <type>political</type>
  </address_component>
  <geometry>
   <location>
    <lat>38.0370570</lat>
    <lng>114.4686650</lng>
   </location>
   <location_type>APPROXIMATE</location_type>
   <viewport>
    <southwest>
     <lat>36.0482067</lat>
     <lng>113.4653687</lng>
    </southwest>
    <northeast>
     <lat>42.6197178</lat>
     <lng>119.8542560</lng>
    </northeast>
   </viewport>
   <bounds>
    <southwest>
     <lat>36.0482067</lat>
     <lng>113.4653687</lng>
    </southwest>
    <northeast>
     <lat>42.6197178</lat>
     <lng>119.8542560</lng>
    </northeast>
   </bounds>
  </geometry>
 </result>
 <result>
  <type>country</type>
  <type>political</type>
  <formatted_address>China</formatted_address>
  <address_component>
   <long_name>China</long_name>
   <short_name>CN</short_name>
   <type>country</type>
   <type>political</type>
  </address_component>
  <geometry>
   <location>
    <lat>35.8616600</lat>
    <lng>104.1953970</lng>
   </location>
   <location_type>APPROXIMATE</location_type>
   <viewport>
    <southwest>
     <lat>18.1535216</lat>
     <lng>73.4994137</lng>
    </southwest>
    <northeast>
     <lat>53.5609740</lat>
     <lng>134.7728100</lng>
    </northeast>
   </viewport>
   <bounds>
    <southwest>
     <lat>18.1535216</lat>
     <lng>73.4994137</lng>
    </southwest>
    <northeast>
     <lat>53.5609740</lat>
     <lng>134.7728100</lng>
    </northeast>
   </bounds>
  </geometry>
 </result>
</GeocodeResponse>

查询结果各字段的含义可以参考Google Map API的Reverse Geocoding (Address Lookup)章节。简化后可以直接判断返回的字符串中是否存在“<short_name>CN</short_name>”作为判定所查询坐标是否在中国的依据。

方法2，根据国家行政边界判定

由于国家行政边界是由多个简单多边形组成的。对多个多边形进行命中测试 (Hit Testing)，只要其中一个多边形测试成功，则表示整个命中测试成功。但多边形的命中测试有些麻烦，更简单的方法是判别点是否在多边形内（Point in polygon(PIP)）。这些算法中简单高效的莫过于是光线投射算法 (Ray casting algorithm)。

光线投射算法的要义是：在二维空间的任意一点射出一条射线，射线穿过多边形边界奇数次则这个点在多边形内，否则在多边形外。此方法适用于复杂多边形。实现此算法往往会限制射线的方向是向右的，这样的好处是简化了许多计算。此算法的一个实现参考1987年Paul Bourke教授所写“Determining if a point lies on the interior of a polygon”的Solution 1。

在 Windows Phone 7 中的实现，首先需要获取到国家行政边界的WGS84坐标数据。Alexey Strakh（链接有恶意软件警告）所开发的gMaps应用中包含了此边界数据。因此，自己可以把数据抠出来。抠出的数据由四部分组成我国的行政边界：大陆、台湾省、海南省、崇明岛。此数据相对来说比较准确，但是边界附近误差较大。每次判别坐标是否在此区域内的计算次数较多，大约需要几百次的几何计算。

此方法的实现代码如下：

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

520

521

522

523

524

525

526

527

528

529

530

531

532

533

534

535

536

537

538

539

540

541

542

543

544

545

546

547

548

549

550

551

552

553

554

555

556

557

558

559

560

561

562

563

564

565

566

567

568

569

570

571

572

573

574

575

576

577

578

579

580

581

582

583

584

585

586

587

588

589

590

591

592

593

594

595

596

597

598

599

600

601

602

603

604

605

606

607

608

609

610

611

612

613

614

615

616

617

618

619

620

621

622

623

624

625

626

627

#region polygon
 
List<Point[]> polygon = new List<Point[]>();
 
private void InitPolygon()
{
    polygon.Add(new Point[]  //Mainland
    {
        new Point(27.32083, 88.91693),
        new Point(27.54243, 88.76464),
        new Point(28.00805, 88.83575),
        new Point(28.1168, 88.62435),
        new Point(27.86605, 88.14279),
        new Point(27.82305, 87.19275),
        new Point(28.11166, 86.69527),
        new Point(27.90888, 86.45137),
        new Point(28.15805, 86.19769),
        new Point(27.88625, 86.0054),
        new Point(28.27916, 85.72137),
        new Point(28.30666, 85.11095),
        new Point(28.59104, 85.19518),
        new Point(28.54444, 84.84665),
        new Point(28.73402, 84.48623),
        new Point(29.26097, 84.11651),
        new Point(29.18902, 83.5479),
        new Point(29.63166, 83.19109),
        new Point(30.06923, 82.17525),
        new Point(30.33444, 82.11123),
        new Point(30.385, 81.42623),
        new Point(30.01194, 81.23221),
        new Point(30.20435, 81.02536),
        new Point(30.57552, 80.207),
        new Point(30.73374, 80.25423),
        new Point(30.96583, 79.86304),
        new Point(30.95708, 79.55429),
        new Point(31.43729, 79.08082),
        new Point(31.30895, 78.76825),
        new Point(31.96847, 78.77075),
        new Point(32.24304, 78.47594),
        new Point(32.5561, 78.40595),
        new Point(32.63902, 78.74623),
        new Point(32.35083, 78.9711),
        new Point(32.75666, 79.52874),
        new Point(33.09944, 79.37511),
        new Point(33.42863, 78.93623),
        new Point(33.52041, 78.81387),
        new Point(34.06833, 78.73581),
        new Point(34.35001, 78.98535),
        new Point(34.6118, 78.33707),
        new Point(35.28069, 78.02305),
        new Point(35.49902, 78.0718),
        new Point(35.50133, 77.82393),
        new Point(35.6125, 76.89526),
        new Point(35.90665, 76.55304),
        new Point(35.81458, 76.18061),
        new Point(36.07082, 75.92887),
        new Point(36.23751, 76.04166),
        new Point(36.66343, 75.85984),
        new Point(36.73169, 75.45179),
        new Point(36.91156, 75.39902),
        new Point(36.99719, 75.14787),
        new Point(37.02782, 74.56543),
        new Point(37.17, 74.39089),
        new Point(37.23733, 74.91574),
        new Point(37.40659, 75.18748),
        new Point(37.65243, 74.9036),
        new Point(38.47256, 74.85442),
        new Point(38.67438, 74.35471),
        new Point(38.61271, 73.81401),
        new Point(38.88653, 73.70818),
        new Point(38.97256, 73.85235),
        new Point(39.23569, 73.62005),
        new Point(39.45483, 73.65569),
        new Point(39.59965, 73.95471),
        new Point(39.76896, 73.8429),
        new Point(40.04202, 73.99096),
        new Point(40.32792, 74.88089),
        new Point(40.51723, 74.8588),
        new Point(40.45042, 75.23394),
        new Point(40.64452, 75.58284),
        new Point(40.298, 75.70374),
        new Point(40.35324, 76.3344),
        new Point(41.01258, 76.87067),
        new Point(41.04079, 78.08083),
        new Point(41.39286, 78.39554),
        new Point(42.03954, 80.24513),
        new Point(42.19622, 80.23402),
        new Point(42.63245, 80.15804),
        new Point(42.81565, 80.25796),
        new Point(42.88545, 80.57226),
        new Point(43.02906, 80.38405),
        new Point(43.1683, 80.81526),
        new Point(44.11378, 80.36887),
        new Point(44.6358, 80.38499),
        new Point(44.73408, 80.51589),
        new Point(44.90282, 79.87106),
        new Point(45.3497, 81.67928),
        new Point(45.15748, 81.94803),
        new Point(45.13303, 82.56638),
        new Point(45.43581, 82.64624),
        new Point(45.5831, 82.32179),
        new Point(47.20061, 83.03443),
        new Point(46.97332, 83.93026),
        new Point(46.99361, 84.67804),
        new Point(46.8277, 84.80318),
        new Point(47.0591, 85.52257),
        new Point(47.26221, 85.70139),
        new Point(47.93721, 85.53707),
        new Point(48.39333, 85.76596),
        new Point(48.54277, 86.59791),
        new Point(49.1102, 86.87602),
        new Point(49.09262, 87.34821),
        new Point(49.17295, 87.8407),
        new Point(48.98304, 87.89291),
        new Point(48.88103, 87.7611),
        new Point(48.73499, 88.05942),
        new Point(48.56541, 87.99194),
        new Point(48.40582, 88.51679),
        new Point(48.21193, 88.61179),
        new Point(47.99374, 89.08514),
        new Point(47.88791, 90.07096),
        new Point(46.95221, 90.9136),
        new Point(46.57735, 91.07027),
        new Point(46.29694, 90.92151),
        new Point(46.01735, 91.02651),
        new Point(45.57972, 90.68193),
        new Point(45.25305, 90.89694),
        new Point(45.07729, 91.56088),
        new Point(44.95721, 93.5547),
        new Point(44.35499, 94.71735),
        new Point(44.29416, 95.41061),
        new Point(44.01937, 95.34109),
        new Point(43.99311, 95.53339),
        new Point(43.28388, 95.87901),
        new Point(42.73499, 96.38206),
        new Point(42.79583, 97.1654),
        new Point(42.57194, 99.51012),
        new Point(42.67707, 100.8425),
        new Point(42.50972, 101.8147),
        new Point(42.23333, 102.0772),
        new Point(41.88721, 103.4164),
        new Point(41.87721, 104.5267),
        new Point(41.67068, 104.5237),
        new Point(41.58666, 105.0065),
        new Point(42.46624, 107.4758),
        new Point(42.42999, 109.3107),
        new Point(42.64576, 110.1064),
        new Point(43.31694, 110.9897),
        new Point(43.69221, 111.9583),
        new Point(44.37527, 111.4214),
        new Point(45.04944, 111.873),
        new Point(45.08055, 112.4272),
        new Point(44.8461, 112.853),
        new Point(44.74527, 113.638),
        new Point(45.38943, 114.5453),
        new Point(45.4586, 115.7019),
        new Point(45.72193, 116.2104),
        new Point(46.29583, 116.5855),
        new Point(46.41888, 117.3755),
        new Point(46.57069, 117.425),
        new Point(46.53645, 117.8455),
        new Point(46.73638, 118.3147),
        new Point(46.59895, 119.7068),
        new Point(46.71513, 119.9315),
        new Point(46.90221, 119.9225),
        new Point(47.66499, 119.125),
        new Point(47.99475, 118.5393),
        new Point(48.01125, 117.8046),
        new Point(47.65741, 117.3827),
        new Point(47.88805, 116.8747),
        new Point(47.87819, 116.2624),
        new Point(47.69186, 115.9231),
        new Point(47.91749, 115.5944),
        new Point(48.14353, 115.5491),
        new Point(48.25249, 115.8358),
        new Point(48.52055, 115.8111),
        new Point(49.83047, 116.7114),
        new Point(49.52058, 117.8747),
        new Point(49.92263, 118.5746),
        new Point(50.09631, 119.321),
        new Point(50.33028, 119.36),
        new Point(50.39027, 119.1386),
        new Point(51.62083, 120.0641),
        new Point(52.115, 120.7767),
        new Point(52.34423, 120.6259),
        new Point(52.54267, 120.7122),
        new Point(52.58805, 120.0819),
        new Point(52.76819, 120.0314),
        new Point(53.26374, 120.8307),
        new Point(53.54361, 123.6147),
        new Point(53.18832, 124.4933),
        new Point(53.05027, 125.62),
        new Point(52.8752, 125.6573),
        new Point(52.75722, 126.0968),
        new Point(52.5761, 125.9943),
        new Point(52.12694, 126.555),
        new Point(51.99437, 126.4412),
        new Point(51.38138, 126.9139),
        new Point(51.26555, 126.8176),
        new Point(51.31923, 126.9689),
        new Point(51.05825, 126.9331),
        new Point(50.74138, 127.2919),
        new Point(50.31472, 127.334),
        new Point(50.20856, 127.5861),
        new Point(49.80588, 127.515),
        new Point(49.58665, 127.838),
        new Point(49.58443, 128.7119),
        new Point(49.34676, 129.1118),
        new Point(49.4158, 129.4902),
        new Point(48.86464, 130.2246),
        new Point(48.86041, 130.674),
        new Point(48.60576, 130.5236),
        new Point(48.3268, 130.824),
        new Point(48.10839, 130.6598),
        new Point(47.68721, 130.9922),
        new Point(47.71027, 132.5211),
        new Point(48.09888, 133.0827),
        new Point(48.06888, 133.4843),
        new Point(48.39112, 134.4153),
        new Point(48.26713, 134.7408),
        new Point(47.99207, 134.5576),
        new Point(47.70027, 134.7608),
        new Point(47.32333, 134.1825),
        new Point(46.64017, 133.9977),
        new Point(46.47888, 133.8472),
        new Point(46.25363, 133.9016),
        new Point(45.82347, 133.4761),
        new Point(45.62458, 133.4702),
        new Point(45.45083, 133.1491),
        new Point(45.05694, 133.0253),
        new Point(45.34582, 131.8684),
        new Point(44.97388, 131.4691),
        new Point(44.83649, 130.953),
        new Point(44.05193, 131.298),
        new Point(43.53624, 131.1912),
        new Point(43.38958, 131.3104),
        new Point(42.91645, 131.1285),
        new Point(42.74485, 130.4327),
        new Point(42.42186, 130.6044),
        new Point(42.71416, 130.2468),
        new Point(42.88794, 130.2514),
        new Point(43.00457, 129.9046),
        new Point(42.43582, 129.6955),
        new Point(42.44624, 129.3493),
        new Point(42.02736, 128.9269),
        new Point(42.00124, 128.0566),
        new Point(41.58284, 128.3002),
        new Point(41.38124, 128.1529),
        new Point(41.47249, 127.2708),
        new Point(41.79222, 126.9047),
        new Point(41.61176, 126.5661),
        new Point(40.89694, 126.0118),
        new Point(40.47037, 124.8851),
        new Point(40.09362, 124.3736),
        new Point(39.82777, 124.128),
        new Point(39.8143, 123.2422),
        new Point(39.67388, 123.2167),
        new Point(38.99638, 121.648),
        new Point(38.8611, 121.6982),
        new Point(38.71909, 121.1873),
        new Point(38.91221, 121.0887),
        new Point(39.09013, 121.6794),
        new Point(39.2186, 121.5994),
        new Point(39.35166, 121.7511),
        new Point(39.52847, 121.2283),
        new Point(39.62322, 121.533),
        new Point(39.81138, 121.4683),
        new Point(40.00305, 121.881),
        new Point(40.50562, 122.2987),
        new Point(40.73874, 122.0521),
        new Point(40.92194, 121.1775),
        new Point(40.1961, 120.4468),
        new Point(39.87242, 119.5264),
        new Point(39.15693, 118.9715),
        new Point(39.04083, 118.3273),
        new Point(39.19846, 117.889),
        new Point(38.67555, 117.5364),
        new Point(38.38666, 117.6722),
        new Point(38.16721, 118.0281),
        new Point(38.1529, 118.8378),
        new Point(37.87832, 119.0355),
        new Point(37.30054, 118.9566),
        new Point(37.14361, 119.2328),
        new Point(37.15138, 119.7672),
        new Point(37.35228, 119.8529),
        new Point(37.83499, 120.7371),
        new Point(37.42458, 121.58),
        new Point(37.55256, 122.1282),
        new Point(37.41833, 122.1814),
        new Point(37.39624, 122.5586),
        new Point(37.20999, 122.5972),
        new Point(37.02583, 122.4005),
        new Point(37.01978, 122.5392),
        new Point(36.89361, 122.5047),
        new Point(36.84298, 122.1923),
        new Point(37.00027, 121.9566),
        new Point(36.75889, 121.5944),
        new Point(36.61666, 120.7764),
        new Point(36.52638, 120.96),
        new Point(36.37582, 120.8753),
        new Point(36.42277, 120.7062),
        new Point(36.14075, 120.6956),
        new Point(36.0419, 120.3436),
        new Point(36.26345, 120.3078),
        new Point(36.19998, 120.0889),
        new Point(35.95943, 120.2378),
        new Point(35.57893, 119.6475),
        new Point(34.88499, 119.1761),
        new Point(34.31145, 120.2487),
        new Point(32.97499, 120.8858),
        new Point(32.63889, 120.8375),
        new Point(32.42958, 121.3348),
        new Point(32.11333, 121.4412),
        new Point(32.02166, 121.7066),
        new Point(31.67833, 121.8275),
        new Point(31.86639, 120.9444),
        new Point(32.09361, 120.6019),
        new Point(31.94555, 120.099),
        new Point(32.30638, 119.8267),
        new Point(32.26277, 119.6317),
        new Point(31.90388, 120.1364),
        new Point(31.98833, 120.7026),
        new Point(31.81944, 120.7196),
        new Point(31.30889, 121.6681),
        new Point(30.97986, 121.8828),
        new Point(30.85305, 121.8469),
        new Point(30.56889, 120.9915),
        new Point(30.33555, 120.8144),
        new Point(30.39298, 120.4586),
        new Point(30.19694, 120.15),
        new Point(30.31027, 120.5082),
        new Point(30.06465, 120.7916),
        new Point(30.30458, 121.2808),
        new Point(29.96305, 121.6778),
        new Point(29.88211, 122.1196),
        new Point(29.51167, 121.4483),
        new Point(29.58916, 121.9744),
        new Point(29.19527, 121.9336),
        new Point(29.18388, 121.8119),
        new Point(29.37236, 121.7969),
        new Point(29.19729, 121.7444),
        new Point(29.29111, 121.5611),
        new Point(29.1634, 121.4135),
        new Point(29.02194, 121.6914),
        new Point(28.9359, 121.4908),
        new Point(28.72798, 121.6113),
        new Point(28.84215, 121.1464),
        new Point(28.66993, 121.4844),
        new Point(28.34722, 121.6417),
        new Point(28.13889, 121.3419),
        new Point(28.38277, 121.1651),
        new Point(27.98222, 120.9353),
        new Point(28.07944, 120.5908),
        new Point(27.87229, 120.84),
        new Point(27.59319, 120.5812),
        new Point(27.45083, 120.6655),
        new Point(27.20777, 120.5075),
        new Point(27.28278, 120.1896),
        new Point(27.14764, 120.4211),
        new Point(26.89805, 120.0332),
        new Point(26.64465, 120.128),
        new Point(26.51778, 119.8603),
        new Point(26.78823, 120.0733),
        new Point(26.64888, 119.8668),
        new Point(26.79611, 119.7879),
        new Point(26.75625, 119.5503),
        new Point(26.44222, 119.8204),
        new Point(26.47388, 119.5775),
        new Point(26.33861, 119.658),
        new Point(26.36777, 119.9489),
        new Point(25.99694, 119.4253),
        new Point(26.14041, 119.0975),
        new Point(25.93788, 119.354),
        new Point(25.99069, 119.7058),
        new Point(25.67996, 119.5807),
        new Point(25.68222, 119.4522),
        new Point(25.35333, 119.6454),
        new Point(25.60649, 119.3149),
        new Point(25.42097, 119.1053),
        new Point(25.25319, 119.3526),
        new Point(25.17208, 119.2726),
        new Point(25.2426, 118.8749),
        new Point(24.97194, 118.9866),
        new Point(24.88291, 118.5729),
        new Point(24.75673, 118.7631),
        new Point(24.52861, 118.5953),
        new Point(24.53638, 118.2397),
        new Point(24.68194, 118.1688),
        new Point(24.44024, 118.0199),
        new Point(24.46019, 117.7947),
        new Point(24.25875, 118.1237),
        new Point(23.62437, 117.1957),
        new Point(23.65919, 116.9179),
        new Point(23.355, 116.7603),
        new Point(23.42024, 116.5322),
        new Point(23.23666, 116.7871),
        new Point(23.21083, 116.5139),
        new Point(22.93902, 116.4817),
        new Point(22.73916, 115.7978),
        new Point(22.88416, 115.6403),
        new Point(22.65889, 115.5367),
        new Point(22.80833, 115.1614),
        new Point(22.70277, 114.8889),
        new Point(22.53305, 114.8722),
        new Point(22.64027, 114.718),
        new Point(22.81402, 114.7782),
        new Point(22.69972, 114.5208),
        new Point(22.50423, 114.6136),
        new Point(22.55004, 114.2223),
        new Point(22.42993, 114.3885),
        new Point(22.26056, 114.2961),
        new Point(22.36736, 113.9056),
        new Point(22.50874, 114.0337),
        new Point(22.47444, 113.8608),
        new Point(22.83458, 113.606),
        new Point(23.05027, 113.5253),
        new Point(23.11724, 113.8219),
        new Point(23.05083, 113.4793),
        new Point(22.87986, 113.3629),
        new Point(22.54944, 113.5648),
        new Point(22.18701, 113.5527),
        new Point(22.56701, 113.1687),
        new Point(22.17965, 113.3868),
        new Point(22.04069, 113.2226),
        new Point(22.20485, 113.0848),
        new Point(21.8693, 112.94),
        new Point(21.96472, 112.824),
        new Point(21.70139, 112.2819),
        new Point(21.91611, 111.8921),
        new Point(21.75139, 111.9669),
        new Point(21.77819, 111.6762),
        new Point(21.61264, 111.7832),
        new Point(21.5268, 111.644),
        new Point(21.52528, 111.0285),
        new Point(21.21138, 110.5328),
        new Point(21.37322, 110.3944),
        new Point(20.84381, 110.1594),
        new Point(20.84083, 110.3755),
        new Point(20.64, 110.3239),
        new Point(20.48618, 110.5274),
        new Point(20.24611, 110.2789),
        new Point(20.2336, 109.9244),
        new Point(20.4318, 110.0069),
        new Point(20.92416, 109.6629),
        new Point(21.44694, 109.9411),
        new Point(21.50569, 109.6605),
        new Point(21.72333, 109.5733),
        new Point(21.49499, 109.5344),
        new Point(21.39666, 109.1428),
        new Point(21.58305, 109.1375),
        new Point(21.61611, 108.911),
        new Point(21.79889, 108.8702),
        new Point(21.59888, 108.7403),
        new Point(21.93562, 108.4692),
        new Point(21.59014, 108.5125),
        new Point(21.68999, 108.3336),
        new Point(21.51444, 108.2447),
        new Point(21.54241, 107.99),
        new Point(21.66694, 107.7831),
        new Point(21.60526, 107.3627),
        new Point(22.03083, 106.6933),
        new Point(22.45682, 106.5517),
        new Point(22.76389, 106.7875),
        new Point(22.86694, 106.7029),
        new Point(22.91253, 105.8771),
        new Point(23.32416, 105.3587),
        new Point(23.18027, 104.9075),
        new Point(22.81805, 104.7319),
        new Point(22.6875, 104.3747),
        new Point(22.79812, 104.1113),
        new Point(22.50387, 103.9687),
        new Point(22.78287, 103.6538),
        new Point(22.58436, 103.5224),
        new Point(22.79451, 103.3337),
        new Point(22.43652, 103.0304),
        new Point(22.77187, 102.4744),
        new Point(22.39629, 102.1407),
        new Point(22.49777, 101.7415),
        new Point(22.20916, 101.5744),
        new Point(21.83444, 101.7653),
        new Point(21.14451, 101.786),
        new Point(21.17687, 101.2919),
        new Point(21.57264, 101.1482),
        new Point(21.76903, 101.099),
        new Point(21.47694, 100.6397),
        new Point(21.43546, 100.2057),
        new Point(21.72555, 99.97763),
        new Point(22.05018, 99.95741),
        new Point(22.15592, 99.16785),
        new Point(22.93659, 99.56484),
        new Point(23.08204, 99.5113),
        new Point(23.18916, 98.92747),
        new Point(23.97076, 98.67991),
        new Point(24.16007, 98.89073),
        new Point(23.92999, 97.54762),
        new Point(24.26055, 97.7593),
        new Point(24.47666, 97.54305),
        new Point(24.73992, 97.55255),
        new Point(25.61527, 98.19109),
        new Point(25.56944, 98.36137),
        new Point(25.85597, 98.7104),
        new Point(26.12527, 98.56944),
        new Point(26.18472, 98.73109),
        new Point(26.79166, 98.77777),
        new Point(27.52972, 98.69699),
        new Point(27.6725, 98.45888),
        new Point(27.54014, 98.31992),
        new Point(28.14889, 98.14499),
        new Point(28.54652, 97.55887),
        new Point(28.22277, 97.34888),
        new Point(28.46749, 96.65387),
        new Point(28.35111, 96.40193),
        new Point(28.525, 96.34027),
        new Point(28.79569, 96.61373),
        new Point(29.05666, 96.47083),
        new Point(28.90138, 96.17532),
        new Point(29.05972, 96.14888),
        new Point(29.25757, 96.39172),
        new Point(29.46444, 96.08315),
        new Point(29.03527, 95.38777),
        new Point(29.33346, 94.64751),
        new Point(29.07348, 94.23456),
        new Point(28.6692, 93.96172),
        new Point(28.61876, 93.35194),
        new Point(28.3193, 93.22205),
        new Point(28.1419, 92.71044),
        new Point(27.86194, 92.54498),
        new Point(27.76472, 91.65776),
        new Point(27.945, 91.66277),
        new Point(28.08111, 91.30138),
        new Point(27.96999, 91.08693),
        new Point(28.07958, 90.3765),
        new Point(28.24257, 90.38898),
        new Point(28.32369, 89.99819),
        new Point(28.05777, 89.48749),
        new Point(27.32083, 88.91693)
    });
    polygon.Add(new Point[]  //Taiwan
    {
        new Point(25.13474, 121.4441),
        new Point(25.28361, 121.5632),
        new Point(25.00722, 122.0004),
        new Point(24.85028, 121.8182),
        new Point(24.47638, 121.8397),
        new Point(23.0875, 121.3556),
        new Point(21.92791, 120.7196),
        new Point(22.31277, 120.6103),
        new Point(22.54044, 120.3071),
        new Point(23.04437, 120.0539),
        new Point(23.61708, 120.1112),
        new Point(25.00166, 121.0017),
        new Point(25.13474, 121.4441)
    });
    polygon.Add(new Point[]  //Hainan
    {
        new Point(19.52888, 110.855),
        new Point(19.16761, 110.4832),
        new Point(18.80083, 110.5255),
        new Point(18.3852, 110.0503),
        new Point(18.39152, 109.7594),
        new Point(18.19777, 109.7036),
        new Point(18.50562, 108.6871),
        new Point(19.28028, 108.6283),
        new Point(19.76, 109.2939),
        new Point(19.7236, 109.1653),
        new Point(19.89972, 109.2572),
        new Point(19.82861, 109.4658),
        new Point(19.99389, 109.6108),
        new Point(20.13361, 110.6655),
        new Point(19.97861, 110.9425),
        new Point(19.63829, 111.0215),
        new Point(19.52888, 110.855)
    });
    polygon.Add(new Point[]  //Chongming
    {
        new Point(31.80054, 121.2039),
        new Point(31.49972, 121.8736),
        new Point(31.53111, 121.5464),
        new Point(31.80054, 121.2039)
    });
}
private bool IsInsideChina(GeoCoordinate positionToCheck)
{
    if (positionToCheck == null || positionToCheck.IsUnknown)
        return false;
    return polygon.Any(s => IsInsidePolygon(s, positionToCheck.Latitude, positionToCheck.Longitude));
}
private bool IsInsidePolygon(Point[] poly, double x, double y)
{
    var index = 0;
    var inside = false;
    var prePoint = poly[0];
    for (index = 1; index < poly.Length; index++)
    {
        var nextPoint = poly[index];
        if (y > Math.Min(prePoint.Y, nextPoint.Y)
            && y <= Math.Max(prePoint.Y, nextPoint.Y)
            && x <= Math.Max(prePoint.X, nextPoint.X)
            && prePoint.Y != nextPoint.Y)
        {
            double xinters = (y - prePoint.Y) * (nextPoint.X - prePoint.X) / (nextPoint.Y - prePoint.Y) + prePoint.X;
            if (prePoint.X == nextPoint.X || x <= xinters)
                inside ^= true;
        }
        prePoint = nextPoint;
    }
    return inside;
}
 
private void MainPage_Loaded(object sender, RoutedEventArgs e)
{
    InitPolygon();
    foreach (var points in polygon)
    {
        var poly = new MapPolyline();
        poly.Locations = new LocationCollection();
        for (int i = 0; i < points.Length; i++)
        {
            poly.Locations.Add(new GeoCoordinate(points[i].X, points[i].Y));
        }
        poly.Stroke = new SolidColorBrush(Colors.Red);
        myMap.Children.Add(poly);
    }
    myMap.SetView(new GeoCoordinate(39.4916649164344, 108.745576123357), 3.7090892722116307);
}
 
#endregion

方法3，根据国家行政边界近似判定

有时候需要一种快速的方法判定，这种快速判定的方法是从Nokia Maps中挖掘出来的。基本思路是：把整个行政区域划分为几个小的矩形，然后再排除掉一些矩形区域。只要一个点在限定的区域内，并且不在排除的区域内，则判定成功，否则失败。下图中蓝色区域为限定区域，红色区域为排除区域。

此方法的实现代码如下：

#region rectangle
 
private class Rectangle
{
    public double West;
    public double North;
    public double East;
    public double South;
    public Rectangle(double latitude1, double longitude1, double latitude2, double longitude2)
    {
        this.West = Math.Min(longitude1, longitude2);
        this.North = Math.Max(latitude1, latitude2);
        this.East = Math.Max(longitude1, longitude2);
        this.South = Math.Min(latitude1, latitude2);
    }
}
 
private static Rectangle[] region = new Rectangle[]
{
    new Rectangle(49.220400, 079.446200, 42.889900, 096.330000),
    new Rectangle(54.141500, 109.687200, 39.374200, 135.000200),
    new Rectangle(42.889900, 073.124600, 29.529700, 124.143255),
    new Rectangle(29.529700, 082.968400, 26.718600, 097.035200),
    new Rectangle(29.529700, 097.025300, 20.414096, 124.367395),
    new Rectangle(20.414096, 107.975793, 17.871542, 111.744104),
 
};
private static Rectangle[] exclude = new Rectangle[]
{
    new Rectangle(25.398623, 119.921265, 21.785006, 122.497559),
    new Rectangle(22.284000, 101.865200, 20.098800, 106.665000),
    new Rectangle(21.542200, 106.452500, 20.487800, 108.051000),
    new Rectangle(55.817500, 109.032300, 50.325700, 119.127000),
    new Rectangle(55.817500, 127.456800, 49.557400, 137.022700),
    new Rectangle(44.892200, 131.266200, 42.569200, 137.022700),
};
 
public static bool IsInsideChina(GeoCoordinate pos)
{
    for (int i = 0; i < region.Length; i++)
    {
        if (InRectangle(region[i], pos))
        {
            for (int j = 0; j < exclude.Length; j++)
            {
                if (InRectangle(exclude[j], pos))
                {
                    return false;
                }
            }
            return true;
        }
    }
    return false;
}
 
private static bool InRectangle(Rectangle rect, GeoCoordinate pos)
{
    return rect.West <= pos.Longitude && rect.East >= pos.Longitude && rect.North >= pos.Latitude && rect.South <= pos.Latitude;
}
 
private void MainPage_Loaded(object sender, RoutedEventArgs e)
{
    DrawRect(region, new SolidColorBrush(Colors.Blue));
    DrawRect(exclude, new SolidColorBrush(Colors.Red));
    myMap.SetView(new GeoCoordinate(39.4916649164344, 108.745576123357), 3.7090892722116307);
}
 
private void DrawRect(Rectangle[] rects, SolidColorBrush brush)
{
    foreach (var rect in rects)
    {
        var poly = new MapPolyline();
        poly.Locations = new LocationCollection();
        poly.Locations.Add(new GeoCoordinate(rect.North, rect.West));
        poly.Locations.Add(new GeoCoordinate(rect.North, rect.East));
        poly.Locations.Add(new GeoCoordinate(rect.South, rect.East));
        poly.Locations.Add(new GeoCoordinate(rect.South, rect.West));
        poly.Locations.Add(new GeoCoordinate(rect.North, rect.West));
        poly.Stroke = brush;
        myMap.Children.Add(poly);
    }
}
 
#endregion

这几种方法的比较

	优	劣	备注
方法1 通过网络地图接口查询	简单、准确信息量大	速度慢依赖网络	可用Google、Baidu地图接口
方法2 根据国家行政边界判定	准确	代码相对较多判别计算次数较多陆地边界数据误差较大	方法和数据从gMaps中挖掘
方法3 根据国家行政边界近似判定	快速相对准确	边界误差较大	方法和数据从Nokia Maps中挖掘