# Using the Capture API ## Background The **AxsunOCTCapture API** provides users of the Axsun [Ethernet/PCIe DAQ](/axsun-knowledge-base/ref-manual/gigabit-ethernet-daq-board.md) with the ability to retrieve digitized data for subsequent display, analysis, archival, or other user process. Refer to the [AxsunOCTCapture Function Reference](https://downloads.axsun.com/public/software/EthernetDAQ/AxsunOCTCaptureAPI_manual/_axsun_o_c_t_capture_8h.html) and sample code projects on the [Software Downloads](/axsun-knowledge-base/other/downloads.md) page for more information about secondary and advanced functionality provided by the Capture API. Any functionality provided in GUI form by the [Image Capture Tool](/axsun-knowledge-base/software-tools/image-capture-tool.md) also relies directly on the Capture API, so [its documentation](/axsun-knowledge-base/software-tools/image-capture-tool.md) provides additional examples of the Capture API's secondary capabilities. {% hint style="info" %} **NOTE:** Become familiar with the [Basic Operation](/axsun-knowledge-base/ref-manual/gigabit-ethernet-daq-board/basic-operation.md#interaction-with-the-axsunoctcapture-library) of the Ethernet/PCIe DAQ prior to reading this document. {% endhint %} ## Installation ### Windows OS Installation of the AxsunOCTCapture library and its dependencies is covered [when installing the Image Capture Tool](/axsun-knowledge-base/guides/integrated-engine/installing-software.md#image-capture-tool-and-axsunoctcapture) GUI. ### Linux OS Installation of the AxsunOCTCapture library and its dependencies is [covered on this page](/axsun-knowledge-base/api-references/axsunoctcapture.dll/linux-installation.md). ## Integrating Into Your Application Basic functionality of the Capture API can be achieved with only several function calls architected as described below. Please refer to source code available in the [AxsunOCTCapture Function Reference ](https://downloads.axsun.com/public/software/EthernetDAQ/AxsunOCTCaptureAPI_manual/index.html)for several basic API integration example programs that highlight the main functionality in the library. * The Capture API is a "plain-old" ANSI C interface which can be directly called from applications coded in native **C or C++**. * **LabVIEW** integration can be achieved using the [Call Library Function Node](http://zone.ni.com/reference/en-XX/help/371361R-01/glang/call_library_function/). * **C#/.NET Framework** integration can be achieved using P/Invoke and the `DllImport` attribute discussed [here](https://docs.microsoft.com/en-us/cpp/dotnet/using-explicit-pinvoke-in-cpp-dllimport-attribute?view=vs-2017). * **Python** integration can be achieved using the [ctypes library](https://docs.python.org/3/library/ctypes.html). ### Starting a Capture Session Starting a Capture session allocates library resources, including the **Main Image Buffer** – the RAM location into which streamed data will be buffered for subsequent retrieval by the user. The Main Image Buffer size should be allocated based on the expected length of a [Burst Record operation](/axsun-knowledge-base/ref-manual/gigabit-ethernet-daq-board/basic-operation.md#live-imaging-burst-record). It is a circular buffer, so allocating too small will limit the length of a Burst Record operation before overflow, and allocating too large will unnecessarily reserve RAM which could be used by other processes. To start a Capture session, call `axStartSession(...)` with a `capacity_MB` argument as the desired number of MB to reserve for the Main Image Buffer. ### Selecting a Capture Interface Once the Capture session is started, select a capture interface (PCIe or Gigabit Ethernet) for acquiring data from an Axsun DAQ using `axSelectInterface(...)`. This step can be skipped if the session involves only loading saved data files from disk rather than capturing new image data from a DAQ. ### Querying Buffer Information At any time following the start of a Capture session and preferably in a loop which executes regularly during image collection, query the current status of the Main Image Buffer using `axGetStatus(...)`. This provides the active state of data streaming (i.e. is the DAQ currently transmitting images or is it idle?), the number of images captured since last reset, and other parameters. ### Retrieving Image Info and Image Data Following the capture of data into the Main Image Buffer and contained in a loop which executes repeatedly during live image display or during playback of previously recorded images, use the `axGetImageInfo(...)` and `axRequestImage(...)` functions to copy image data from the Main Image Buffer into user memory for subsequent interaction as desired. Alternatively, an event-driven approach is available to asynchronously respond to new images via a callback rather than the traditional polling approach. ### Getting Info and Error Messages Use `axGetMessage(...)` to learn additional information about the session status and `axGetErrorString(...)` to describe the source of potential error codes returned from AxsunOCTCapture function calls. ### Stopping a Capture Session Call `axStopSession(...)` to release interfaces and free resources that were initially allocated when the Capture session was started. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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