R3XA Specification

Version : 2024.7.1

Yet another metadata file format whose goal is to provide a data representation scheme compatible with the variety of data types encountered in experimental and computational photomechanics, and to provide a convenient framework for software coupling and data fusion.

General structure

Section	Description
header	Top-level metadata fields (title, description, version, authorship and links).
settings	Experimental setup and specimen metadata.
data_sources	Sensors and processing blocks that produce data.
data_sets	Data containers linked to one or more data sources.

Header

Field	Type	Required	Description
title	string	Yes	Title of the data sets.
description	string	Yes	Description of the data sets.
version	“2024.7.1” (fixed)	Yes	Version of the schema used.
authors	string	Yes	Names, ORCID, IDHAL…
date	string	Yes	Global date of the experiment (YYYY-MM-DD).
repository	string		URL to the repository where the dataset is stored.
documentation	string		URI to the documentation (pdf)
license	string		Public domain, CC-BY, …

Settings

Experimental parameters should be the specimen, patterning technique and machines used (light, testing rig, environmental chamber…). Describe the experimental techniques/apparatus and devices used / light / environment chamber…

Allowed item kinds: Generic | Specimen | Testing Machine | Stereorig

Generic experimental setup (settings/generic)

Generic setup: testing device, environmental chamber, lights…

Field	Type	Required	Description
id	string	Yes	ID of the setting.
kind	“settings/generic” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the setting.
description	string	Yes	Description of the setting.
documentation	string		Path to external documentation/information
associated_data_sources	array[Data source id]		List of datasources linked to this setting

Specimen (settings/specimen)

Specimen.

Field	Type	Required	Description
id	string	Yes	ID of the setting.
kind	“settings/specimen” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the specimen.
description	string	Yes	Description of the specimen.
cad	string		Path to the design of the specimen.
sizes	array[Unit]	Yes	Sizes of the specimen.
patterning_technique	string		Patterning technique used on the specimen.
patterning_feature_size	Unit		Characteristic size of the pattern.

Stereo rig (settings/stereorig)

Multicamera stereo rig.

Field	Type	Required	Description
id	string	Yes	ID of the setting.
kind	“settings/stereorig” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the stereo rig.
description	string	Yes	Description of the stereo rig.
stereo_angle	Unit	Yes	Stereo angle between the camera axes.
calibration_target_type	string		Type of calibration board.
calibration_target_size	array[Unit]		Parameters of the calibration board.
associated_data_sources	array[Data source id]		List of cameras of the rig

Testing machine (settings/testing_machine)

any type of testing machine.

Field	Type	Required	Description
id	string	Yes	ID of the setting.
kind	“settings/testing_machine” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the testing machine.
description	string	Yes	Description of the testing machine.
type	string	Yes	e.g. compression, tensile, torsion, fatigue…
manufacturer	string		Manufacturer, vendor or software editor.
model	string		Model of the source or software version.
documentation	string		filename
capacity	unsigned integer		load capacity
associated_data_sources	array[Data source id]		List of associated sources (extensometers, load cells)

Data Sources

A data source is a procedure or a system that generates a data set. If it is a sensor then its parameters must be specified. If it is an analysis, its parameters are specified along with the input parameters. It also indicates the dimension, the number of components and the unit of the output data.

Allowed item kinds: Generic | Camera | Infrared | Tomograph | Load Cell | Strain Gauge | Point Temperature | Dic Measurement | Mechanical Analysis | Identification | Strain Computation

Generic data source (data_sources/generic)

A data source is a procedure or a system that generates a data set. If it is a sensor then his parameters must be specified. If it is an analysis specifies his parameters are specified along with the input parameters. It also indicates the dimension, the number of components and the unit of the output data.

Field	Type	Required	Description
id	string	Yes	ID of the data source
kind	“data_sources/generic” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the data source.
description	string	Yes	Description of the data source.
input_data_sets	array[Data set id]		Data sets IDs serving as inputs of the source.
output_components	unsigned integer	Yes	Number of components or channels of the ouput data.
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	must be one of: point, curve, surface or volume.
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string	Yes	Manufacturer, vendor or software editor.
model	string	Yes	Model of the source or software version.
documentation	string		Documentation filename, path or URL
uncertainty	Unit		Quantification of data uncertainty.

Visible Camera (data_sources/camera)

Generic camera in visible range.

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/camera” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the camera.
description	string		Description of the camera.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components or channels of the ouput data.
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer name, Brand.
model	string		Camera model.
documentation	string		Documentation filename, path or URL
image_size	array[Unit]	Yes	Size of the image length unit squared.
field_of_view	array[Unit]		Size of the field of view in length unit squared.
image_scale	Unit		Scale of the image in pixels per length unit.
focal_length	Unit		Focal length of the lens in length unit.
lens	string		Lens manufacturer and model names.
filter	string		Filter type, manufacturer and model.
aperture	string		Aperture of the lens, example: f/8
exposure	Unit		Exposure time in time unit.
standoff_distance	Unit		Distance between the camera and the sample.
uncertainty	Unit		Estimation of image noise.

Infrared Camera (data_sources/infrared)

Generic infrared camera

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/infrared” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the infrared camera.
description	string		comments and additional informations
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of channels of the ouput data
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’.
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer, Brand
model	string		Model
documentation	string		Documentation filename, path or URL
image_size	array[Unit]	Yes	Size of the image length unit squared.
field_of_view	array[Unit]		Size of the field of view in length unit squared.
image_scale	Unit		Scale of the image in pixels per length unit.
focal_length	Unit		Focal length of the lens in lenght unit.
lens	string		Camera lens manufacturer and model names.
filter	string		Filter type, manufacturer and model.
aperture	string		Aperture of the lens.
exposure	Unit		Exposure time in time unit.
standoff_distance	Unit		Standoff distance between the camera and the sample in length unit.
bandwidth	array[Unit]	Yes	Bandwidth [item0, item1]
emissivity	Unit		Emissivity
transmissivity	Unit		Transmissivity
nuc_file	string		Non Uniformity Correction
calibration_file	string		filename
uncertainty	Unit		estimation of image noise.

Tomograph X-Ray (data_sources/tomograph)

Generic tomograph

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/tomograph” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Title of the tomograph.
description	string		Description of the tomograph.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of channels of the ouput data.
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’ for radios or ‘volume’ for scans.
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer, vendor or software editor.
model	string		Model or software version.
documentation	string		Documentation filename, path or URL
image_size	array[Unit]	Yes	Size of the image pixels.
field_of_view	array[Unit]		Size of the field of view in length unit.
image_scale	Unit		Scale of the image in pixels per length unit.
source	string	Yes	Source characteristics.
voltage	Unit		Used voltage.
current	Unit		electric current.
detector	string		electric current.
scan_duration	Unit		Scan duration
target	string		reflexion target.
tube_to_detector_distance	Unit		Distance between the tube and the detector.
source_to_object_distance	Unit		Distance between the source and the object.
number_of_projections	unsigned integer		number of radiographs.
angular_amplitude	Unit		amplitude in degree, example: 360
aquisition_param_file	string		filename
reconstruction_param_file	string		filename
uncertainty	Unit		estimation of image noise or artifacts.

Load Cell (data_sources/load_cell)

Load cell, Force cell

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/load_cell” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Load cell name
description	string		Description of the load cell
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components of the ouput data, example 1 for single axis or 6 for 6-axis sensors
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘point’
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer, vendor, brand.
model	string		Model.
documentation	string		Documentation filename, path or URL
type	string		(e.g. wheatstone, piezzo-electric, FSR).
capacity	Unit	Yes	Capacity of the load cell / Force range.
uncertainty	Unit		Quantification of data uncertainty.

Strain Gauge (data_sources/strain_gauge)

Strain gauge, Rosette, Extensometer…

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/strain_gauge” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Strain gauge name
description	string		Description of the load cell
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components of the ouput data, example: 1 or 3 for rosette.
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘point’
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer, Vendor or brand.
model	string		Model.
documentation	string		Documentation filename, path or URL
length	Unit	Yes	Gauge or measuring length
uncertainty	Unit		Uncertainty or resolution of strain.

Point Temperature (data_sources/point_temperature)

thermocouples, Resistance Temperature Detectors (RTDs), thermistor, pyrometer…

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/point_temperature” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Thermometer name
description	string		Description of thermometer
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components of the ouput data, should be 1
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘point’
output_units	array[Unit]	Yes	Unit of the output data.
manufacturer	string		Manufacturer, vendor or software editor.
model	string		Model or software version.
documentation	string		Documentation filename, path or URL
range	array[Unit]	Yes	Temperature range [item0, item1]
emissivity	Unit		Pyrometer emissivity
uncertainty	Unit		uncertainty or resolution.

Digital Image Correlation measurement (data_sources/dic_measurement)

DIC, DVC, Stereo DIC

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/dic_measurement” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Name of the DIC measurement.
description	string		Description of the DIC measurement.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’ for DIC or ‘volume’ for DVC
output_units	array[Unit]	Yes	examples: pixels, voxels, length unit…
manufacturer	string		Software editor.
model	string		Software version.
documentation	string		Documentation filename, path or URL
subset_size	array[Unit]		Size of the subset length unit squared.
step_size	Unit		distance between two adjacent subsets
mesh	string		Finite Element or BSpline mesh: filename or specimen setting id
image_filtering	string		Type of filter and kernel
interpolant	string		Subpixel interpolation: linear, cubic spline
matching_criterion	string	Yes	ZNSSD, ZNCC or other …
shape_function	string		affine, quadratic, linear triangles TRI3 …
camera_model	string		no, pinhole, distortions modes…
camera_parameters	string		filename or list of parameters
regularization_type	string		strong/weak + type: gradient, elastic…
regularisation_length	Unit		length or weight
uncertainty	Unit		e.g. uncertainty on the output field

Mechanical analysis (data_sources/mechanical_analysis)

numerical simulation of a mechanical model

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/mechanical_analysis” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Name of the data analysis.
description	string		Description of the mechanical model.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’ for 2D or ‘volume’ for 3D
output_units	array[Unit]	Yes	examples: %, microdefs…
manufacturer	string	Yes	Software name.
model	string		Software version.
documentation	string		Documentation filename, path or URL
parameters	array[Unit]		constitutive, geometric, loading or numerical parameters
uncertainty	Unit		estimation of numerical errors

Parameter identification (data_sources/identification)

inverse problem or model updating

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/identification” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Name of the inverse analysis.
description	string		Description of the identification method and parameters used.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’ for 2D or ‘volume’ for 3D
output_units	array[Unit]	Yes	examples: %, microdefs…
manufacturer	string		Software name.
model	string		Software version.
documentation	string		Documentation filename, path or URL
parameters	array[Unit]		constitutive, geometric, loading or numerical parameters
uncertainty	Unit		estimation of identification uncertainty

Computing strains from displacement field (data_sources/strain_computation)

Post-processing measured of simulated displacement fields to compute strains

Field	Type	Required	Description
id	string	Yes	ID of the data source.
kind	“data_sources/strain_computation” (fixed)	Yes	Only required for specs implementation purposes.
title	string		Name of the data analysis.
description	string		Additional description of the way strains are computed from displacements.
input_data_sets	array[Data set id]		Data sets IDs serving as an input to the source.
output_components	unsigned integer	Yes	Number of components
output_dimension	“point” | “curve” | “surface” | “volume”	Yes	should be ‘surface’ for 2D or ‘volume’ for 3D
output_units	array[Unit]	Yes	examples: %, microdefs…
manufacturer	string		Software name.
model	string		Software version.
documentation	string		Documentation filename, path or URL
virtual_strain_gauge_size	Unit	Yes
displacement_filtering	string		Type of filter and kernel
strain_filtering	string		Type of filter and kernel
uncertainty	Unit		estimation of uncertainty on the output

Data Sets

A data set gives the organisation of the measured or generated data and time resolution.

Allowed item kinds: Generic | File | List

Generic data set (data_sets/generic)

Description of the data set.

Field	Type	Required	Description
id	string	Yes	ID of the data set.
kind	“data_sets/generic” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the data set.
description	string	Yes	Description of the data set.
file_type	string	Yes	MIME type of the file.
path	string	Yes	Relative path to the data file.
data_sources	array[Data source id]	Yes	List of IDs of the data sources.

Data set (single file) (data_sets/file)

When all the timestamps and data is stored in a single tablular like file (like csv or txt). If the timestamps and data are in two separate files they should be in the same folder.

Field	Type	Required	Description
id	string	Yes	ID of the data set.
kind	“data_sets/file” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the data set.
description	string	Yes	Description of the data set.
folder	string		Relative path to the folder containing the timestamps and data file(s).
data_sources	array[Data source id]	Yes	List of IDs of the data sources.
time_reference	number	Yes	Time serving as a reference to the whole data set.
keywords	array[string]		List of keywords.
timestamps	Data set file	Yes	Path and range to the timestamps file
data	Data set file	Yes	Path and range to the data file

Data set (list of files) (data_sets/list)

When all the data is stored in separated files (like a list of images). They should all be in the same folder.

Field	Type	Required	Description
id	string	Yes	ID of the data set.
kind	“data_sets/list” (fixed)	Yes	Only required for specs implementation purposes.
title	string	Yes	Title of the data set.
description	string	Yes	Description of the data set.
path	string		Relative path to the data folder.
file_type	string	Yes	MIME type of the data files.
data_sources	array[Data source id]	Yes	List if IDs of the data sources.
time_reference	Unit	Yes	Time serving as a reference to the whole data set.
keywords	array[string]		List of keywords.
timestamps	array[number]	Yes	List of the timestamps.
data	array[string]	Yes	List of the data files.

Appendix — Common Types

Setting id

ID of a setting.

Property	Value
type	string

Data set id

ID of a data set.

Property	Value
type	string

Data source id

ID of a data source.

Property	Value
type	string

Data set file

Field	Type	Required	Description
filename	string	Yes
file_type	string		MIME type of the file.
delimiter	string
data_range	string
kind	“data_set_file” (fixed)	Yes	Only required for specs implementation purposes

Unit

Field	Type	Required	Description
title	string		Title of the unit.
value	number		Numerical value.
unit	string	Yes	Sign of the unit.
scale	number		Factor with respect to the standard system
kind	“unit” (fixed)	Yes	Only required for specs implementation purposes

unsigned integer

Unsigned int

Property	Value
type	integer