NxLib API > HowTo's > Basic Camera Operations > Reading/Writing Camera Parameter Files

This example shows how to open a camera, apply a saved parameter set from a json parameter file saved from NxView and modify single parameters thereafter.

Format of JSON parameter files

A parameter file is a text file and contains the complete camera tree structure with all node names and values in JSON format. When saving parameter files from NxView you can choose to save the tree below two different nodes:

•the subtree Parameters of the Camera node (see picture, red frame), or

•the entire Camera node (see picture, blue frame), which includes the Parameters subtree, but additionally all other information like the camera calibration, model name, serial number, etc.

Parameter-Subtrees

Depending on the content of the parameter file you have different options how to restore the parameters onto an open camera:

•Full Camera node in json file

oOverwrite the entire Camera node of you opened camera with the JSON content of the parameter file:
This will restore all camera settings in the Parameters subnode, but will also apply the calibration data from the Calibration subnode of the parameter file onto the Calibration node of the opened camera. Make sure to not overwrite the calibration with a calibration of a different camera.

oExtract the Parameters subtree from the file and overwrite only the camera's Parameters subtree with this. The extraction is easily done by saving the entire JSON content of the file into a temporary NxLib tree item. The camera will then keep its calibration and adopt all other settings from the file.

•Only Parameters subtree in json file

oHere you can directly overwrite the camera's Parameters node with the content of the file. The camera will keep its calibration and adopt all other settings from the file.

Code Examples

Open camera and read parameter file

NxLibItem root; // References the tree's root item at path "/"

//replace "1234" with your camera's serial number:
NxLibItem camera = root[itmCameras][itmBySerialNo]["1234"]; // References the camera's item at path "/Cameras/BySerialNo/1234"

// Call the Open command to open the camera
NxLibCommand open(cmdOpen); // Note: the variable name 'open' does not matter; the constant 'cmdOpen'
                            // specifies the name of the command to be executed when '.execute()' is called
                            // on the object.
// Set parameters for the command
open.parameters()[itmCameras] = "1234"; // Insert the serial number of the camera to be opened into the Cameras parameter of Open
open.execute();

// At this point the parameter tree under /Cameras/BySerialNo/1234/Parameters contains the default values for all settings.

// Assume we saved a file 'params.json' from NxView that we now want to load
// First we read the json file as normal text file into a string variable

std::ifstream file("params.json");
if (file.is_open() && file.rdbuf()) {
   // You can use the std::stringstream class to read a textfile:
   std::stringstream buffer;
   buffer << file.rdbuf();
   std::string const& fileContent = buffer.str();

   // We now have the entire json representation of the parameter set
   // in the string variable 'fileContent'

   // In order to detect if the file contains the parameters only, or the entire camera node we simply write it into
   // a temporary NxLib node "/tmp" and check if it contains a subitem 'Parameters'; if it does, we only use this
   // subitem to rewrite the camera's parameter tree, otherwise we assume that the file contained the parameter subtree only

   NxLibItem tmp("/tmp");
   tmp.setJson(fileContent); // Parse json file content into temporary item
   if (tmp[itmParameters].exists()) {
      // Looks like we had a file containing the full camera node; let's just use the parameters subtree to overwrite
      // the camera's parameter subtree
      camera[itmParameters].setJson(tmp[itmParameters].asJson(), true); // writeableNodesOnly = true silently skips
                                                                        // read-only nodes instead of failing when
                                                                        // encountering a read-only node
   } else {
      // It seems that our file only contained the parameters node, because we don't have Parameters as a subnode;
      // We then use the entire content of the temporary node to rewrite the camera's parameters node
      camera[itmParameters].setJson(tmp.asJson(), true); // with writebleNodesOnly = true, see comment above
   }
} else {
   // File could not be read
   ...
}

* References the tree's root item at path "/"
open_framegrabber ('Ensenso-NxLib', 0, 0, 0, 0, 0, 0, 'default', 0, 'Raw', -1, 'false', 'Item', '/', 0, 0, RootHandle)

* Open the camera and reference the camera's item at path "/Cameras/BySerialNo/1234"
* replace "1234" with your camera's serial number
open_framegrabber ('Ensenso-NxLib', 0, 0, 0, 0, 0, 0, 'default', 0, 'Raw', -1, 'false', 'Stereo', '1234', 0, 0, CameraHandle)

* At this point the parameter tree under /Cameras/BySerialNo/1234/Parameters contains the default values for all settings.

* Assume we saved a file 'params.json' from NxView that we now want to load
* First we read the json file as normal text file into a string variable
get_framegrabber_param (RootHandle, 'file://C:/MyJsonFiles/params.json', FileContent)

* We now have the entire json representation of the parameter set in the string variable 'fileContent'

* In order to detect if the file contains the parameters only, or the entire camera node we simply write it into
* a temporary NxLib node "/tmp" and check if it contains a subitem 'Parameters'; if it does, we only use this
* subitem to rewrite the camera's parameter tree, otherwise we assume that the file contained the parameter subtree only

set_framegrabber_param (RootHandle, 'tmp', ['apply', FileContent])
get_framegrabber_param (RootHandle, 'type:tmp/Parameters', ItemType)
if (ItemType == 'Object')
    * Looks like we had a file containing the full camera node; let's just use the parameters subtree to overwrite
    * the camera's parameter subtree
    get_framegrabber_param (RootHandle, 'tmp/Parameters', ParameterSubItem)
    set_framegrabber_param (CameraHandle, 'Parameters' , ['apply', ParameterSubItem])
else
    * It seems that our file only contained the parameters node, because we don't have Parameters as a subnode;
    * We then use the entire content of the temporary node to rewrite the camera's parameters node
    set_framegrabber_param (CameraHandle, 'Parameters' , ['apply', FileContent])
endif

Write parameter file

As explained above there are two options to write the settings file, one containing the entire camera node, and one containing only the parameters subtree. In the example the constant 'StoreEntireCameraNode' switches between these two options.