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一、需求将las格式的点云数据转换为cesium能加载渲染的3dtiles格式(pnts)。二、具体实现步骤2.1 依赖开源库gdal库点云数据多为投影坐标系cesium渲染需要的是地理坐标系所以需要gdal库进行坐标转换。LASzip库读写las的库。Qt 、osg等库不是必须可以不用。我的代码其他地方需要这两个库所以就用上了。2.2点云读取使用LASzip库读取点云到内存。这里在具体程序实现的时候需要注意分块策略因为有些点云数据动则几十个G如果不进行分块处理对硬件压力太大了。具体的分块思路应该是现对点云数据构建索引我代码中用的四叉树构建的点云索引然后根据点云数量及范围对点云进行分块每次处理的时候针对某一块进行处理。而且分块后方便后续并行加速处理。2.3 lod构建第一步根据2.2中的分块结果读取其中的某一块点云数据统计其点个数和外界包围盒。第二步判断统计的点云数据个数是否大于指定的阈值(该值是3dtiles中每个pnts文件的最大点数量)。如果小于指定阈值则该块不需要进行分块将该块中的全部点写入pnts。如果小于指定阈值则以该块外界包围盒(矩形)中心为分界点创建四个子节点块该块则被称为根节点。第三步针对第二步中得到的根节点块和子节点块继续按照步骤二中的规则对四个子节点进行分块。具体是否分块还是按照节点中的点云数与指定阈值的大小来决定。以此循环直到所有的节点都不能再分块为止。这样就完成了整个点云的lod构建。上述方法描述起来比较拗口其实用程序实现的时候只需要进行递归调用即可实现部分实现代码如下QSharedPointerscially::OSGIndexNode Build3dtiles(const std::vectorPointCI* pointSet, std::vectorunsigned int pointIndex, osg::BoundingBox boundingBox, osg::BoundingBox boundingBoxLevel0, const std::string saveFilePath, const std::string strBlock, unsigned int level, unsigned int childNo, ExportMode exportMode, const scially::SpatialTransform transform, const scially::TileStorage storage) { // filename of self, left, right std::string saveFileName, pageName1, pageName2, pageName3, pageName4; if (level 0) { saveFileName strBlock; } else { char tmpSaveFileName[100]; sprintf(tmpSaveFileName, %s%s%d%s%d, strBlock.c_str(), _L, level, _, childNo); saveFileName.assign(tmpSaveFileName); saveFileName /*saveFilePath / */ saveFileName; } //********** 1 2 ********** //********** 3 4 ********** char tmpPageName1[100], tmpPageName2[100], tmpPageName3[100], tmpPageName4[100]; sprintf(tmpPageName1, %s%s%d%s%d, strBlock.c_str(), _L, level 1, _, childNo * 4); pageName1.assign(tmpPageName1); sprintf(tmpPageName2, %s%s%d%s%d, strBlock.c_str(), _L, level 1, _, childNo * 4 1); pageName2.assign(tmpPageName2); sprintf(tmpPageName3, %s%s%d%s%d, strBlock.c_str(), _L, level 1, _, childNo * 4 2); pageName3.assign(tmpPageName3); sprintf(tmpPageName4, %s%s%d%s%d, strBlock.c_str(), _L, level 1, _, childNo * 4 3); pageName4.assign(tmpPageName4); // handle leaf case if (pointIndex.size() _maxPointNumPerOneNode || level _maxTreeLevel) { //double rangeValue boundingBox.radius() / scially::SPLIT_PIXEL / 32; double geometricError scially::osgBoundingSize(boundingBoxLevel0) / scially::SPLIT_PIXEL / 16 / (pow(2.0, level)); auto pntsNode QSharedPointerscially::PntsTile::create(); pntsNode-tileName() QString::fromStdString(saveFileName); pntsNode-fileName() QString::fromStdString(strBlock); pntsNode-geometricError() geometricError; pntsNode-tileFolder() QString::fromStdString(saveFilePath); pntsNode-m_suffix .pnts; pntsNode-m_refine ADD; pntsNode-boundingBox() boundingBox; QString outFileName pntsNode-relativeNodePath(pntsNode-m_suffix); QByteArray pntsBuffer; osg::Vec3d tileCenter transform.transform(boundingBox.center()); if (write2Pnts(pointSet, pointIndex, osg::Vec3d(0, 0, 0), pntsBuffer)) { if (!storage.saveFile(outFileName, pntsBuffer)) { qWarning(saveFile pnts failed!); return nullptr; } return pntsNode; } else { qWarning(write2Pnts failed!); return nullptr; } } // prepare box AxisInfo midAxisInfo; osg::BoundingBox boundingBox1; osg::BoundingBox boundingBox2; osg::BoundingBox boundingBox3; osg::BoundingBox boundingBox4; midAxisInfo FindMidAxis(boundingBox, boundingBox1, boundingBox2, boundingBox3, boundingBox4); // split self, child1, child2, child3, child4 float interval (float)pointIndex.size() / (float)_maxPointNumPerOneNode; int count -1; std::vectorunsigned int selfPointSetIndex; std::vectorunsigned int child1PointSetIndex; std::vectorunsigned int child2PointSetIndex; std::vectorunsigned int child3PointSetIndex; std::vectorunsigned int child4PointSetIndex; for (int i 0; i pointIndex.size(); i) { int tmp int((float)i / interval); if (tmp count selfPointSetIndex.size() _maxPointNumPerOneNode) { count tmp; selfPointSetIndex.push_back(pointIndex[i]); } else { PointCI tmpPoint pointSet-at(pointIndex[i]); if (tmpPoint.P[0]midAxisInfo.midx tmpPoint.P[1]midAxisInfo.midy) { child1PointSetIndex.push_back(pointIndex[i]); } else if (tmpPoint.P[0] midAxisInfo.midx tmpPoint.P[1] midAxisInfo.midy) { child2PointSetIndex.push_back(pointIndex[i]); } else if (tmpPoint.P[0] midAxisInfo.midx tmpPoint.P[1] midAxisInfo.midy) { child3PointSetIndex.push_back(pointIndex[i]); } else { child4PointSetIndex.push_back(pointIndex[i]); } } } // export //double rangeValue boundingBox.radius() / scially::SPLIT_PIXEL / 32; double geometricError scially::osgBoundingSize(boundingBoxLevel0) / scially::SPLIT_PIXEL / 16 / (pow(2.0, level)); auto pntsNode QSharedPointerscially::PntsTile::create(); pntsNode-tileName() QString::fromStdString(saveFileName); pntsNode-fileName() QString::fromStdString(strBlock); pntsNode-geometricError() geometricError; pntsNode-tileFolder() QString::fromLocal8Bit(saveFilePath.c_str()); pntsNode-m_suffix .pnts; pntsNode-m_refine ADD; pntsNode-boundingBox() boundingBox; QString outFileName pntsNode-relativeNodePath(pntsNode-m_suffix); QByteArray pntsBuffer; osg::Vec3d tileCenter transform.transform(boundingBox.center()); if (write2Pnts(pointSet, selfPointSetIndex, osg::Vec3d(0, 0, 0), pntsBuffer)) { if (!storage.saveFile(outFileName, pntsBuffer)) { qWarning(saveFile pnts failed!); return nullptr; } } else { qWarning(write2Pnts failed!); return false; } // recursive left if (child1PointSetIndex.size()) { auto n Build3dtiles(pointSet, child1PointSetIndex, boundingBox1, boundingBoxLevel0, saveFilePath, strBlock, level 1, childNo * 4, exportMode, transform, storage); if (n) { pntsNode-append(n); } child1PointSetIndex.swap(std::vectorunsigned int()); } if (child2PointSetIndex.size()) { auto n Build3dtiles(pointSet, child2PointSetIndex, boundingBox2, boundingBoxLevel0, saveFilePath, strBlock, level 1, childNo * 4 1, exportMode, transform, storage); if (n) { pntsNode-append(n); } child2PointSetIndex.swap(std::vectorunsigned int()); } if (child3PointSetIndex.size()) { auto n Build3dtiles(pointSet, child3PointSetIndex, boundingBox3, boundingBoxLevel0, saveFilePath, strBlock, level 1, childNo * 4 2, exportMode, transform, storage); if (n) { pntsNode-append(n); } child3PointSetIndex.swap(std::vectorunsigned int()); } if (child4PointSetIndex.size()) { auto n Build3dtiles(pointSet, child4PointSetIndex, boundingBox4, boundingBoxLevel0, saveFilePath, strBlock, level 1, childNo * 4 3, exportMode, transform, storage); if (n) { pntsNode-append(n); } child4PointSetIndex.swap(std::vectorunsigned int()); } return pntsNode; }2.4 写pnts按照2.3构建起点云的lod后我们得到的是一个包含多个节点的四叉树四叉树中每个节点代表一块点数量不超过指定阈值的点云数据。我们要将所有的节点写入pnts文件。例如根节点点云数量为s指定的阈值是t则我们在写根节点的pnts文件时需要从s中均匀的抽取出t个点。只需要计算出间隔取样距离即可float interval s/t;按interval间隔取点写入pnts。下面的代码是单个pnts文件的写入实现完全按照cesium官方给出的pnts格式进行写入的。写颜色的时候有强度渲染和RGB渲染之分。下面是写pnts代码截取。//写pnts代码 bool write2Pnts(const std::vectorPointCI* pointSet, std::vectorunsigned int pointIndex, const osg::Vec3d center, QByteArray buffer) { if (pointIndex.size() 0) { return false; } osg::ref_ptrosg::Vec3Array pointArray new osg::Vec3Array; osg::ref_ptrosg::Vec4Array colorArray new osg::Vec4Array; for (std::vectorunsigned int::iterator i pointIndex.begin(); i ! pointIndex.end(); i) { PointCI tmpPoint pointSet-at(*i); pointArray-push_back(tmpPoint.P); if (_colorMode ColorMode::Debug) { colorArray-push_back(_colorBar[0]); } else if (_colorMode ColorMode::RGB) { colorArray-push_back( osg::Vec4(Color8BitsToFloat(tmpPoint.C[0]), Color8BitsToFloat(tmpPoint.C[1]), Color8BitsToFloat(tmpPoint.C[2]), 1.f)); } else if (_colorMode ColorMode::IntensityGrey) { colorArray-push_back(_colorBar[tmpPoint.I]); } else if (_colorMode ColorMode::IntensityBlueWhiteRed) { colorArray-push_back(_colorBar[tmpPoint.I]); } else if (_colorMode ColorMode::IntensityHeightBlend) { float x (tmpPoint.P.z() - this-_boundingBoxGlobal.zMin()) / (this-_boundingBoxGlobal.zMax() - this-_boundingBoxGlobal.zMin()); //// sigmoid //x (x - 0.5) * 4; //x 1. / (1. exp(-5 * x)); int index x * 255; index std::max(0, std::min(255, index)); osg::Vec4 color _colorBar[index]; color color * 0.9 color * (tmpPoint.I / 255.) * 0.1; color.w() 1.0; colorArray-push_back(color); } } QDataStream dataStream(buffer, QIODevice::WriteOnly); dataStream.setByteOrder(QDataStream::LittleEndian); // TODO: batch table // feature table QByteArray featureTableJsonByte; { QJsonObject featureTableJson; featureTableJson[POINTS_LENGTH] (int)pointArray-size(); if (center ! osg::Vec3d(0, 0, 0)) { featureTableJson[RTC_CENTER] QJsonArray({ center.x(), center.y(), center.z() }); } QJsonObject posjson; posjson.insert(byteOffset, 0); featureTableJson[POSITION] posjson; if (colorArray-size() ! 0) { QJsonObject colorjson; long long length pointArray-size() * 3 * 4; colorjson.insert(byteOffset, length); featureTableJson[RGB] colorjson; } featureTableJsonByte QJsonDocument(featureTableJson) .toJson(QJsonDocument::Compact); while (featureTableJsonByte.size() % 8 ! 0) { featureTableJsonByte.append( ); } } QByteArray featureTableBinary; { std::ostringstream oss; for (int i 0; i pointArray-size(); i) { osg::Vec3f pt pointArray-at(i); oss.write((char*)(pt[0]), sizeof(float)); oss.write((char*)(pt[1]), sizeof(float)); oss.write((char*)(pt[2]), sizeof(float)); } for (int i 0; i colorArray-size(); i) { osg::Vec4f color colorArray-at(i); uint8_t r color[0] * 255; uint8_t g color[1] * 255; uint8_t b color[2] * 255; oss.write((char*)(r), sizeof(uint8_t)); oss.write((char*)(g), sizeof(uint8_t)); oss.write((char*)(b), sizeof(uint8_t)); //oss.write((char*)(colorn[3]), sizeof(int)); } oss.flush(); std::string str oss.str(); featureTableBinary.append(str.data(), str.size()); while (featureTableJsonByte.size() % 8 ! 0) { featureTableJsonByte.append( ); } } uint32_t version 1; uint32_t featureTableJSONByteLength featureTableJsonByte.size(); uint32_t featureTableBinaryByteLength featureTableBinary.size(); uint32_t batchTableJSONByteLength 0; uint32_t batchTableBinaryByteLength 0; uint32_t headerLength 28 featureTableJSONByteLength featureTableBinaryByteLength batchTableJSONByteLength batchTableBinaryByteLength; //header { dataStream.writeRawData(pnts, 4); dataStream version; dataStream headerLength; dataStream featureTableJSONByteLength; dataStream featureTableBinaryByteLength; dataStream batchTableJSONByteLength; dataStream batchTableBinaryByteLength; } dataStream.writeRawData(featureTableJsonByte.data(), featureTableJsonByte.size()); dataStream.writeRawData(featureTableBinary.data(), featureTableBinary.size()); return true; }2.5写json按照3dtiles数据格式要求需要有一个总的tileset.json文件然后每个tile中需要有根节点的json文件。
