3. YAML input data format for `gama-local`

YAML is a human-readable data-serialization language. It is commonly used for configuration files and in applications where data is being stored or transmitted. YAML targets many of the same communications applications as Extensible Markup Language but has a minimal syntax which intentionally differs from SGML. Wikipedia

In version 2.12 YAML support was added for gama-local as an alternative to the existing XML input format. The YAML support is limited only to conversion program gama-local-yaml2gkf but it may be fully integrated in gama-local program later.

In GNU Gama YAML documents are based on four main nodes

   defaults:

   description:

   points:

   observations:

Where defaults and description are optional and points and observations are mandatory and each can be used only once. The order of the nodes is arbitrary.

Lets start with a full example

   defaults:
     sigma-apr : 5
     conf-pr:    0.95

   description: >-
     Example: a simple network

   points:
     - id:  1783
       y:   453500.000
       x:   104500.000
       adj: xy

     - id:  2044
       y:   461000.000
       x:   101000.000
       fix: xy

   observations:
     - from: 1783
       obs:
         - type:  direction
           to:    776
           val:   29.51661
           stdev: 2.0

         - type:  direction
           to:    351
           val:   94.22790
           stdev: 2.0

     - from: 351
       obs:
         - type:  direction
           to:    2044
           val:   170.48370
           stdev: 2.0

         - type:  distance
           to:    1783
           val:   5522.668
           stdev: 10.0

     - from: 462
       obs:
         - type:  direction
           to:    2505
           val:   299.99973
           stdev: 2.0

The description node is clearly the simplest one, it just describes a simple text attached to the data. But still there may be a catch. If the description contains colon (:), it might confuse the YAML parser because it would be interpreted as a syntax construction. To escape colon(s) in the description node we use >- to prevent colons to be interpreted as a syntax construction. Always using >- with description is a safe bet.

The data structure of the YAML document is defined by indentation, this principle was inspired by Python programming language, where indentation is very important; Python uses indentation to indicate a block of code.

Practically all attribute names used in out YAML format are the same as in XML data format.

Lets have a look on some more examples. Within observations: section we can define height differerence (another kind of a measurement).

   observations:

     - height-differences:
         - dh:
             from: A
             to  : B
             val : 25.42
             dist: 18.1     # distance in km
         - dh:
             from: B
             to:   C
             val:  10.34
             dist:  9.4

Two remaining observation types are vectors and coordinates.

   observations:
     - vectors:
       - vec:
           from: A
           to: S
           dx: 60.0070
           dy: 35.0053
           dz: 54.9953
       - vec:
           from: B
           to: S
           dx: -39.9974
           dy: 34.9928
           dz: 54.9976

and

   observations:
     - coordinates:
       - id: 403
         x: 1054612.59853
         y: 644373.60446
       - id: 407
         x: 1054821.17131
         y: 644025.97479

   ....

       - cov-mat:
           dim: 20
           band: 19
           upper-part:
             6.7589719e+01 1.8437742e+01 1.3176856e+01 ...

Typically any observation set can define its covariance matrix.

You may wish to compare YAML and XML data files available from Gama tests suite in tests/gama-local/input directory (files *.gkf and *.yaml).

The gama-local input xml data can be formally validated against the XSD definition. Unfortunatelly there is no formal definition of YAML input. Within the testing suite of GNU Gama project we have a test that validates all available YAML files converted to XML by the formal XSD definition, see the test xmllint-gama-local-yaml2gkf.

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3.1 YAML support

GNU Gama YAML input format is dependent on C++ YAML-CPP library written by Jesse Beder https://yaml.org/. With the Gama primary build system (autotools) you need to install the library at your system, for example on Debian like systems it is libyaml-cpp-dev package.

A different solution is used in the alternative Gama cmake based build, where the source codes are expected to be available from the lib directory. Change to "GNU Gama sources"/lib and clone the git repository.

   cd "GNU Gama sources"/lib
   git clone https://github.com/jbeder/yaml-cpp