In addition to the shape data, there are three types of variables in MorphoJ. These are identifiers of observations, classifiers that provide information about group membership, and covariates that are continuous external data.
Each landmark configuration has an identifier, a sequence of characters that serves to identify the specimen. For instance, a species name such as "Homo sapiens", a sequence of coded information such as "C001V3mli2r1", or a combination of both as in "Homo sapiens f057s".
MorphoJ obtains identifiers with the coordinate data when these are imported initially, and passes them along with the data during analyses. There are tools for extracting information from the identifiers or otherwise manipulating them.
If a text file is used for importing data, the identifier needs to be the first entry of the line representing a specimen.
Identifiers can contain any characters except tab stops, commas, or semicolons . Most notably, identifiers can include spaces (as in "Homo sapiens") or various special characters (%, &, @ etc.). More restrictive conditions apply when importing data from sources other than text files.
It is helpful if the identifiers in a dataset are unique, although there is no absolute requirement for this. Particularly, if the user intends to link datasets, the identifiers should be unique in each dataset and agree between datasets because the identifiers are used as the criterion to match corresponding observations.
Classifiers provide information about properties of the observations, such as the sex, juvenile or adult, origin, habitat, patient or control, or any other categorical criterion that may be used for defining the membership of groups of observations.
Like identifiers, classifiers are arbitrary sequences of letters, numbers, or special characters. Therefore, there is no need to code information as numbers. For instance, males and females can be coded as "f" and "m" rather than as "1" and "2", which may reduce the chance of mixing up the codes.
If the identifiers consist of coded information, classifiers can be extracted from the identifiers. Alternatively, they can be imported from a text file.
Classifiers can be used to define group membership for analyses such as canonical variate analysis, or they can be used to subdivide data sets or for averaging observations.
Covariates are variables providing quantitative information about the specimens. Typical covariates are body mass, age, year of birth, percentage of leaves in the diet, or any other quantity that an investigator may want to relate to the morphological information.
Note that centroid size of the configurations is computed by MorphoJ and is usually not treated as a covariate.
Covariates are imported into MorphoJ from text files.