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一、OpenIGTLink

OpenIGTLink，可以简称为IGTL。它是一个专供医疗应用的网络通信库。IGTL可以应用各种传感器、手术机器人和成像仪等的数据传输。OpenIGTLink是有一系列的协议在底层支持的，它是跨平台的，应用也非常简单。
OpenIGTLink迭代还是比较快的，目前已经到了3.0版本。更多的对其的技术相关资料，请查阅相关的资料或访问其官方地址及github。

二、IGTL的应用

IGTL在医疗行业应用还是比较多的，它的优点是相对简单，支持的场景也相对较多。缺点就是相对简单，无法处理一些复杂的网络应用。不过话又说回来，在医疗行业这种场景下，一般也没有复杂的网络应用，一般就是几台机器通信，能复杂到哪儿。
IGTL的应用重点还是在业务上，即它支持医疗行业的设备间的状态（STATUS）、图像（IMAGE）和命令（COMMAND）等各种消息格式。其实如果认真的向下看Message构成的情况就会发现，和传统的网络通信中定义的协议没有什么不同。封装起来的目的就是为了简单好用。

三、Supra中的应用

在初步简单了解了一下IGTL后，就看一下在Supra中如何使用这个库，相关代码如下：
1、做为服务端使用

	void OpenIGTLinkOutputDevice::initializeOutput(){log_info("IGTL: server port: ", m_server->GetServerPort());if (m_server->CreateServer(m_port) != 0) {m_isReady = false;}else {m_isReady = true;//Wait asynchronously for the connectionwaitAsyncForConnection();}}template <typename T>void OpenIGTLinkOutputDevice::sendImageMessageTemplated(shared_ptr<const USImage> imageData){static_assert(std::is_same<T, uint8_t>::value ||std::is_same<T, int16_t>::value ||std::is_same<T, float>::value,"Image only implemented for uchar, short and float at the moment");auto properties = imageData->getImageProperties();if (properties->getImageType() == USImageProperties::BMode ||properties->getImageType() == USImageProperties::Doppler){double resolution = properties->getImageResolution();vec3s imageSize = imageData->getSize();igtl::ImageMessage::Pointer pImageMsg = igtl::ImageMessage::New();pImageMsg->SetDimensions((int)imageSize.x, (int)imageSize.y, (int)imageSize.z);pImageMsg->SetSpacing(resolution, resolution, resolution);if (is_same<T, uint8_t>::value){pImageMsg->SetScalarTypeToUint8();}if (is_same<T, int16_t>::value){pImageMsg->SetScalarTypeToInt16();}if (is_same<T, float>::value){pImageMsg->SetScalarType(igtl::ImageMessage::TYPE_FLOAT32);}pImageMsg->SetEndian(igtl::ImageMessage::ENDIAN_LITTLE);igtl::Matrix4x4 m;igtl::IdentityMatrix(m);m[0][0] = -1;m[1][1] = -1;pImageMsg->SetMatrix(m);pImageMsg->SetNumComponents(1);pImageMsg->SetDeviceName(m_streamName.c_str());pImageMsg->AllocateScalars();igtl::TimeStamp::Pointer pTimestamp = igtl::TimeStamp::New();double timestampSeconds;double timestampFrac = modf(imageData->getSyncTimestamp(), &timestampSeconds);pTimestamp->SetTime((uint32_t)timestampSeconds, (uint32_t)(timestampFrac*1e9));pImageMsg->SetTimeStamp(pTimestamp);auto imageContainer = imageData->getData<T>();if (!imageContainer->isHost()){imageContainer = make_shared<Container<T> >(LocationHost, *imageContainer);}size_t numElements = imageSize.x * imageSize.y * imageSize.z;memcpy(pImageMsg->GetScalarPointer(), imageContainer->get(), numElements * sizeof(T));pImageMsg->Pack();int sendResult = m_clientConnection->Send(pImageMsg->GetPackPointer(), pImageMsg->GetPackSize());if (sendResult == 0) //when it could not be sent{m_isConnected = false;log_info("IGTL: Lost connection. Waiting for next connection.");waitAsyncForConnection();}}}void OpenIGTLinkOutputDevice::waitAsyncForConnection(){if (m_pConnectionThread && m_pConnectionThread->joinable()){m_pConnectionThread->join();}m_pConnectionThread = unique_ptr<thread>(new thread([this]() {log_info("IGTL: waiting for connection");m_clientConnection = m_server->WaitForConnection();m_isConnected = true;log_info("IGTL: got connection!");}));}

代码很简单，如果配合着IGTL自带的示例代码会更容易弄明白。

2、做为客户端使用

void TrackerInterfaceIGTL::startAcquisition() {m_callFrequency.setName("TrIGTL");while (getRunning()) {if (!m_connected) {lock_guard<mutex> lock(m_objectMutex);connectToSever();}//------------------------------------------------------------// Wait for a replyif (m_connected) {igtl::MessageHeader::Pointer headerMsg;headerMsg = igtl::MessageHeader::New();headerMsg->InitPack();int rs = m_socket->Receive(headerMsg->GetPackPointer(),headerMsg->GetPackSize());{lock_guard<mutex> lock(m_objectMutex);if (rs == 0) {logging::log_warn("TrackerInterfaceIGTL: Connection closed.");closeSocket();continue;}if (rs != headerMsg->GetPackSize()) {logging::log_warn("TrackerInterfaceIGTL: Message size information ""and actual data size don't match.");closeSocket();continue;}if (!m_frozen) {headerMsg->Unpack();if (strcmp(headerMsg->GetDeviceType(), "TDATA") == 0) {receiveTrackingData(headerMsg);} else {m_socket->Skip(headerMsg->GetBodySizeToRead(), 0);}}}} else {logging::log_warn("TrackerInterfaceIGTL: Could not reconnect to the server '",m_hostname, ":", m_port, "'. Retrying in ", m_reconnectInterval,"s.");duration<long, std::milli> sleepDuration =milliseconds((long long)round(m_reconnectInterval * 1e3));this_thread::sleep_for(sleepDuration);}}{lock_guard<mutex> lock(m_objectMutex);closeSocket();}
}void TrackerInterfaceIGTL::connectToSever() {if (!m_connected) {int r = m_socket->ConnectToServer(m_hostname.c_str(), m_port);if (r != 0) {m_connected = false;logging::log_warn("TrackerInterfaceIGTL: Could not reconnect to the server '",m_hostname, ":", m_port, "'");} else {m_connected = true;logging::log_info("TrackerInterfaceIGTL: Connected to the server '",m_hostname, ":", m_port, "'");}}
}void TrackerInterfaceIGTL::closeSocket() {m_connected = false;logging::log_warn("TrackerInterfaceIGTL: Closing socket to the server '",m_hostname, ":", m_port, "'");m_socket->CloseSocket();
}bool TrackerInterfaceIGTL::receiveTrackingData(igtl::MessageHeader::Pointer &header) {//------------------------------------------------------------// Allocate TrackingData Message Classigtl::TrackingDataMessage::Pointer trackingData;trackingData = igtl::TrackingDataMessage::New();trackingData->SetMessageHeader(header);trackingData->AllocatePack();// Receive body from the socketm_socket->Receive(trackingData->GetPackBodyPointer(),trackingData->GetPackBodySize());// Deserialize the transform data// If you want to skip CRC check, call Unpack() without argument.int c = trackingData->Unpack(1);bool crcFine = (c & igtl::MessageHeader::UNPACK_BODY) > 0;if (crcFine) // if CRC check is OK{std::vector<TrackerData> trackerData;// compute float timestamp format from IGTL representationuint32_t timestampSeconds;uint32_t timestampFrac;trackingData->GetTimeStamp(&timestampSeconds, &timestampFrac);double timestamp = (double)timestampSeconds + ((double)timestampFrac) / 1e9;int nElements = trackingData->GetNumberOfTrackingDataElements();for (int i = 0; i < nElements; i++) {igtl::TrackingDataElement::Pointer trackingElement;trackingData->GetTrackingDataElement(i, trackingElement);igtl::Matrix4x4 igtlMatrix;trackingElement->GetMatrix(igtlMatrix);TrackerData::Matrix matrix;matrix[0 + 0] = igtlMatrix[0][0];matrix[0 + 1] = igtlMatrix[0][1];matrix[0 + 2] = igtlMatrix[0][2];matrix[0 + 3] = igtlMatrix[0][3];matrix[4 + 0] = igtlMatrix[1][0];matrix[4 + 1] = igtlMatrix[1][1];matrix[4 + 2] = igtlMatrix[1][2];matrix[4 + 3] = igtlMatrix[1][3];matrix[8 + 0] = igtlMatrix[2][0];matrix[8 + 1] = igtlMatrix[2][1];matrix[8 + 2] = igtlMatrix[2][2];matrix[8 + 3] = igtlMatrix[2][3];matrix[12 + 0] = igtlMatrix[3][0];matrix[12 + 1] = igtlMatrix[3][1];matrix[12 + 2] = igtlMatrix[3][2];matrix[12 + 3] = igtlMatrix[3][3];trackerData.push_back(TrackerData(matrix, 100, 666, trackingElement->GetName(), timestamp));}auto pTrackingDataSet =make_shared<TrackerDataSet>(trackerData, timestamp, timestamp);addData<0>(pTrackingDataSet);m_callFrequency.measure();} else {logging::log_warn("TrackerInterfaceIGTL: IGTL message CRC error, skipping message");}return crcFine;
}
void TrackerInterfaceIGTL::initializeDevice() {// try to connect already here, so we are directly good to go!lock_guard<mutex> lock(m_objectMutex);m_socket = igtl::ClientSocket::New();connectToSever();
}

这段代码是接收TrackerData的，代码也很容易理解。其实主要是要和IGTL中的相关格式对应，此处就是TDATA，所以按照其协议的说明一看就明白了。

四、总结

国外的框架库，一个比较让人头疼的就是里面用了非常多的其它相关的库。这样的好处当然很明显，就是完成具体的工作的效率会大幅提高。但对于学习者来说就比较麻烦了，需要不断的学习这个库那个库，然后才能把整个框架运行起来并初步掌握。
但真正掌握后会发现，写这方面的代码会简单很多，至少比自己想象的要简单很多！如果做应用开发的话，这确实是一个好的方法！