MEGS_Log uses schemas to define the order and type
of fields present within some borehole file formats.
Schemas are named and defined using the
MEGS_Log config file or the
Schema Editor. You can also use
the schema editor to import schemas from Prolog 4.x files.
Schemas supplied with MEGS_Log
The config file installed with MEGS_Log contains a number of example
schemas:
Prolog21: A schema suitable for use with
version 2.1 Prolog format files. Schemas for use with Prolog 2.1 format
files always have 25 fields.
Prolog3: A schema suitable for use with a
version 3 Prolog format files with 43 fields in Prolog.
PL3Example: Another schema suitable for use
with a version 3 Prolog format file, specifically the example Prolog file
supplied with MEGS_Log.
CSVExample: A schema suitable for use with
the example CSV format file supplied with MEGS_Log.
Fields
Each field in a schema has a type that determines how MEGS_Log should process
the data for that field. Some fields types are only relevant for unit
properties, while other field types are relevant for bot units and element
properties.
Bottom: The field contains the depth of the
bottom of a unit.
Percentage: The field contains the proportion
(as a percentage) of a unit occupied by an element.
Rocktype: The field contains the rocktype
of an element.
Sample: The field contains the sample
number for a unit.
Ply: The field contains the ply name for
a unit.
String: The field contains a descriptive
string for a unit or element.
Real: The field contains a descriptive
number (that can include fractional values) for a unit or element.
Integer: The field contains a descriptive
whole number for a unit or element.
Thickness: The field contains the true
thickness of a unit. The true thickness is the difference between
the top and bottom depths of a unit.
Recovered: The field contains the
recovered thickness of a unit - the thickness of the unit
based on inspection of core (or similar) from the hole. Recovered
thickness is generally less than true thickness due to core loss.
Seam: The field contains the seam name
for a unit.
Top: The field contains the top depth
of a unit.
A schema that is valid for use by MEGS_Log must contain at least:
A rocktype field
(so MEGS_Log knows how to draw each unit or element).
Either a bottom or
thickness field (so MEGS_Log knows where the
bottom of each unit is).
Schemas that are not valid are ignored by MEGS_Log.
A schema may over-specify the depth to the bottom of each unit,
for example by including both bottom
and top fields. In this case
MEGS_Log will check the over-specified information when loading
a borehole and report errors if the values in the fields do not
reconcile (for example, if the bottom
of a unit is not the same depth as the top
of the underlying unit).
If you want to use MEGS_Log to label units with seam names, or seam
and ply names, then the schema for the borehole must have
seam, or seam
and ply fields.
Similarly, if you want to use MEGS_Log to label units with sample
numbers, then the schema for the borehole must have a
sample field.
Schemas and Prolog
When working with Prolog files there are some additional restrictions
on schemas:
Schemas intended for use on Prolog version 2.1 or 3 format files
(but not Prolog 4.x) must have two more spare fields at the end of the
schema than otherwise expected given the number of fields required by
Prolog. These additional fields simply correspond to end of record
markers in the Prolog file, and are not available for data.
Schemas for use with Prolog 2.1 need a total of 25 fields (including
the extra STRING fields at the end of the schema). The number of fields
for a schema intended to be used with a Prolog 3 or Prolog 4.x file can
vary.
For all Prolog versions supported by MEGS_Log, the first three fields
in the schema must be the ROCKTYPE field, followed by the PERCENTAGE field,
followed by the SEAM field (if you intend to use MEGS_Log to assign seams
and/or plies to units).
The last three fields in the schema (apart from the separator fields
in the case of schemas intended for use with Prolog 2.1 or Prolog 3)
must be the RECOVERED field, followed by the THICKNESS field, followed
by the BOTTOM field.