TECHNICAL ASPECTS (GeM+)
Section [OVERVIEW:ASPECTES_TÈCNICS] (REL file)

This subsection includes the technical information needed to handle the file, such as the number of columns and rows in a raster file or the name and address of the arc file in the polygon layers in a POL format file.

Due to their special characteristics, GeM+ considers the majority of the keys in this subsection as obligatory.

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Name of the GeM+ entry: File type
Name of the REL file key: FileType

Description and considerations: The type of file containing the information on the geographical objects. Typically the raster and structured vector files are binary and the unstructured vector files are ASCII. MiraMon can also import raster files in ASCII format.

This key corresponds to the "file type" key in the older documentation files used for unstructured rasters and vectors. The key was not used in the older documentation files of structured vectors.

Follows the proposal of: GeM+

Obligatory according to GeM+: Yes

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (contains information about the layer)

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Name of GeM+ entry: Layer size
Name of REL file key: (not stored in the REL file, it is deduced dynamically)

Description and considerations: This entry gives information about the size, in bytes, of the files that make up the layer. It does not consider the size of related tables or thesauruses or possible REL files. Generally a map database is made up of more than one file and for this reason the value of this metadata entry considers the size of two or three principal files in the data base:

The button "i" of GeM+ gives information about which files have been used to calculate the layer size. For example:

It is not possible to change this information since it is always calculated dynamically in a standard way. The user may define a layer size in the entry User size and in the User size description.

Follows the proposal of: GeM+

Obligatory according to GeM+: Calculated dynamically.

Cardinality: 1 Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (Holds information on the layer)

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Name of GeM+ entry: User size
Name of REL file key: MidaUsuari

Description and considerations: This entry allows the user to save a different numerical value from that shown in the Layer size entry. This information is useful as the user often wants to have an approximate idea of the overall size of the disk space taken up by a database taking account of the related files (thesaurus, documentation files, etc), or for storing the size of the compressed layer (*.mmz), etc. It is possible to describe this size in the entry User size description. P>Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: User size description
Name of REL file key: DescMidaUsuari

Description and considerations: This entry allows the user to save a text description of the elements considered when defining the value of the User size entry. Since this entry depends on the User size entry it is not possible to define it unless there is a valid User size. Furthermore, if the User size entry is deleted the description is automatically deleted also.

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Data model
Name of REL file key: (not stored in the REL file, it is deduced dynamically)

Description and considerations: This entry tries to give information about the type of spatial representation used for the layer. There are two broad representation models: vector and raster. The first uses geometric objects (points, lines and polygons) to represent objects or properties of the real world (for example, land use or the positions of buildings, streams, roads, etc.). Raster, on the other hand, is based on a regular grid overlaying the territory, dividing it into equal sections, generally in the form of squares. In this way the properties of the territory are represented by assigning to each of these entities (called raster cells) a numeric value that identifies or quantifies the property. The first model places the emphasis on the objects of the territory and their attributes (mapping and delimiting these) whilst the raster model places the emphasis on the position over the territory (What is found at each location?).

This entry can take the values: "raster", "structured vector" and "unstructured vector". The value of this entry can be deduced as a function of the extension of the graphical file in which it is stored:

In the ISO standard this entry corresponds to the MD_SpatialRepresentation section which refers to the mechanism used to represent the spatial information. This section can be specified with MD_GridSpatialRepresentation or as MD_VectorSpatialRepresentation which correspond to our raster and vector models respectively. In the ISO standard the difference between structured and unstructured vectors is noted in the topologyLevel entry (within the MD_VectorSpatialRepresentation section).

Follows the proposal of: ISO

Obligatory according to ISO: Deduced dynamically.

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of the GeM+ entry: Object type
Name of the REL file key: (It is not saved in the REL file, it is dynamically deduced)

Description and considerations: This key indicates the type of object used to represent space in the data set.

In the case of structured vector layers or images, this key is not saved in the REL since it can be deduced from the letter before the extension of the REL file name: T for points, N for nodes, A for arcs, P for polygons, and I for rasters (images, etc; the cases I.rel and J.rel correspond to the same object type: raster cell).

In the case of unstructured vectors this information is known from the "object type :" key in the older documentation file DVC (version 4 does not allow metadata files that substitute this type of file).

For vectors, in the ISO standard this entry corresponds to the geometricObjectsType entry in the MD_GeometricObjects section that depends on the MD_VectorSpatialRepresentation section.

Follows the proposal of: ISO

Obligatory according to ISO: It is dynamically deduced

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (contains information about the layer)

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Name of GeM+ entry: Number of objects (or Number of cells)
Name of REL file key: (not stored in the REL file, it is deduced dynamically)

Description and considerations: This entry gives information about the number of objects used by the layer to represent reality.

In the case of vectors its value can be known by dynamically consulting the database file. In the case of rasters this number is obtained by multiplying the number of rows by the number of columns and the user is shown the "Number of cells".

For vector this entry corresponds to the geometricObjectCount entry in the MD_GeometricObjects section which depends on the MD_VectorSpatialRepresentation section of the ISO standard.

For rasters, the ISO standard allows the properties of each dimension of the raster (typically 2-D: x and y) to be documented, one of which is the entry dimensionSize which corresponds to the number of elements along this axis, that is the number of columns or rows (for the x and y directions respectively).

Follows the proposal of: ISO

Obligatory according to ISO: Deduced dynamically.

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Disk Location
Name of REL file key: (not stored in the REL file, it is deduced dynamically)

Description and considerations: This entry tries to give information about the location on the disk of the layer. This information is obtained directly from the system and for this reason it is deduced dynamically and is not stored in the REL file.

It is possible to document other alternative locations (for example, back up copies, user copies, etc.)

Follows the proposal of: GeM+

Obligatory according to GeM+: Deduced dynamically.

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Alternative location
Name of REL file key: UbicacioAlternativa (see the key in case of raster and vector)

Description and considerations: This entry allows the user to save other alternative locations (for example, back-up copies, user copies, etc.).

It is necessary to distinguish between existing but empty alternative locations and non-existent alternative locations. This difference is made by selecting or not the option "alternative location". If the option is selected the alternative location will be saved in the metadata. If the option is unselected the alternative location is deleted.

In the case of a multiband layer a different value of this key can be documented, for each band, that is different from the general value (see the section Thematic Information ). For this reason in GeM+ (when dealing with multiband layers) there is a radial button that allows either the general data or the data on the selected band to be displayed (the selection of the band is made using a pull-down menu or the forward and back buttons located in the upper part of GeM+).

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Alphanumeric database
Name of REL file key: (not stored in the REL file, it is deduced dynamically)

Description and considerations: The alphanumeric database, that is the database containing the attributes of structured vector data (it is only found with this data format), has the same name and location as the graphical database of the cartographic data, but with an additional letter to indicate the type of object and the extension DBF. This information is obtained directly from the system and for this reason it is deduced dynamically and is not stored in the REL file.

It is possible to document other alternative alphanumeric databases (for example, associated thesaurus, tables in other formats, etc.)

Follows the proposal of: GeM+

Obligatory according to GeM+: Deduced dynamically.

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Alternative alphanumeric database
Name of REL file key: BaseAlternativa (see the key in case of raster and vector)

Description and considerations: This entry allows the user to save other alternative alphanumeric databases (for example, associated thesaurus, tables in other formats, etc.).

It is necessary to distinguish between existing but empty alternative databases and non-existent alternative databases. This difference is made by selecting or not the option "alternative alphanumeric database". If the option is selected the alternative database will be saved in the metadata. If the option is unselected this text is deleted.

In the case of a multiband layer a different value of this key can be documented, for each band, that is different from the general value (see the section Thematic Information). For this reason in GeM+ (when dealing with multiband layers) there is a radial button that allows either the general data or the data on the selected band to be displayed (the selection of the band is made using a pull-down menu or the forward and back buttons located in the upper part of GeM+).

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of the GeM+ entry: Comments
Name of the REL file key: comment#

Description and considerations: All the sections could allow comments using comment# keys but in this version of GeM+ this is only included in this section. The comments of the older documentation files are stored in this section by default.

In the case of automatically generated multi-band layers only the comments from the first band forming the layer are taken from the older documentation file and stored by GeM+.

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: N

Key type: C

AppliesToLayer: Yes
AppliesToSeries: Yes

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Name of the GeM+ entry: Columns
Name of the key in the REL file: columns

Description and considerations: The number of columns in the image. This key only applies to raster files in IMG format. Changing the value may make it impossible to display the layer. The key corresponds to the "columns" entry in the older documentation files.

The JPEG, JPEG2000 or MrSID raster files store this information in the headers of the binary files so the information is shown in GeM+ but it cannot be modified or saved in the REL file.

In the case of a multi-band layer it is possible to document a specific value for this key for each layer different from the general value (see the Thematic Information section). This is why there is a radial button in GeM+ (when dealing with a multi-band layer) that allows either the general data or the data on the selected band to be displayed (this choice is made using the pull-down menu or the forward and back buttons in the upper part of the GeM+).

To avoid incoherent values between the different GeM+ keys and to maintain the implicit relationship between the number of columns, the number of rows, the cell size (in both X and Y directions) and the extents of the layer, it is not possible to directly change the value of this key. In order to change it the option "Change..." must be selected. This opens a dialog box for modifying all these parameters in a coherent way (Changes in the colums,rows, cell size and extents).

This entry is equivalent to the dimensionSize in the ISO standard, where it is defined as the number of elements along an axis (or dimension), that is, the number of columns (for the x dimension).

Follows the proposal of: the FGDC

Obligatory according to the FGDC: Yes

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No

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Name of the GeM+ entry: Rows
Name of the key in the REL file: rows

Description and considerations: The number of rows in the image. This key only applies to raster files in IMG format. Changing the value may make it impossible to display the layer. The key corresponds to the "rows" entry in the older documentation files.

The JPEG, JPEG2000 or MrSID raster files store this information in the headers of the binary files so the information is shown in GeM+ but it cannot be modified or saved in the REL file.

In the case of a multi-band layer it is possible to document a specific value for this key for each layer different from the general value (see the Thematic Information section). This is why there is a radial button in GeM+ (when dealing with a multi-band layer) that allows either the general data or the data on the selected band to be displayed (this choice is made using the pull-down menu or the forward and back buttons in the upper part of the GeM+).

To avoid incoherent values between the different GeM+ keys and to maintain the implicit relationship between the number of columns, the number of rows, the cell size (in both X and Y directions) and the extents of the layer, it is not possible to directly change the value of this key. In order to change it the option "Change..." must be selected. This opens a dialog box for modifying all these parameters in a coherent way (Changes in the colums,rows, cell size and extents).

This entry is equivalent to the dimensionSize in the ISO standard, where it is defined as the number of elements along an axis (or dimension), that is, the number of rows (for the y dimension).

Follows the proposal of: the FGDC

Obligatory according to the FGDC: Yes

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No

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Name of GeM+ entry: Platform and instrument information
Name of the REL file key: OVERVIEW:ASPECTES_TECNICS:PLAT_INSTR_INFO

Description and considerations: The information about the platform and the instrument is made up of a set of metadata entries grouped together in an independent box of the Manager and a section of the REL file. This set of entries only applies to raster images containing photos, satellite images, etc. The descriptions of the different entries that form this section are found grouped in the Platform and instrument information section.

Follows the proposal of: FGDC

Obligatory according to the FDGC: Yes

Cardinality: 1

Key type: composite

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: JPEG Quality
Name of REL file key: QualitatJPEG

Description and considerations: The JPEG image format (implementation IJPEG) is a high compression format that presents some degradation: the values of the decompressed image are close to the original image but are not always the same. This key only applies to raster files in JPEG format.

This metadata entry saves the inforamtion about the quality of the image (that has been degraded) with respect to the original. The quality of the compression should be given as a percentage. Low values indicate poor quality but high compression. For more information consult the application help JPEGIMG.

Follows the proposal of: GeM+

Obligatory according to GeM+: Yes

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (holds information on the Layer)

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Name of GeM+ entry: Scanning resolution (DPI)
Name of REL file key: ResolucioEscanneig_DPI and ResolucioEscanneig_Y_DPI

Description and considerations: The resolution used to scan a paper document, such as a printed map or a photograph (analogue aerial photography). Although according to the international system of units (SI) it is recommended to express this in pixels per centimetre (ppcm) or in pixels per milimetre (ppmm) it is usually expressed in dots per inch (dpi) also called pixels per inch (ppi), and it is in these units that they are stored in the .REL file. To convert from dpi to ppcm divide by 2.54 and to convert from dpi to ppmm divide by 25.4.

The scanning resolution may differ in the X and Y directions so the GeM+ has two keys "Scanner Resolution in X" and "Scanner Resolution in Y" which are stored in two separate keys, if necessary, in the REL.

In the case of a multiband layer it is possible to document, for each band, a different value of this key from the general value (see the section on Thematic Information). It is for this reason that there is a radial button in the GeM+ (for multiband layers) that allows the display of general data or data for the selected band. (This selection is made using the pulldown lists or the forward and back buttons located in the upper part of GeM+).

In photogrammetric scanners the scanning resolution is sometimes given in micrometers per pixel instead of dpi. To convert from micrometers (µm) per pixel to dpi, divide 25400 by the number of microns per pixel. (For example, an image scanned at 12 µm/pixel corresponds to 2117 dpi).

Note: Micrometers per pixel are also sometimes refers to as "microns", or by using the Greek letter "µ". These denominations are contrary to the SI specification so it is better to always use "µm/pixel".

Photographs obtained using a digital metric camera can also use this term. In this case the scanner resolution in X can be calculated by dividing the number of columns of the image by the width of the CCD camera expressed in inches (consult the technical specifications of the camera) and similarly for the Y resolution.

JPEG raster format files contain this information in the binary file header so this is shown in GeM+ but cannot be modified in the .REL file.

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (contains information on the Layer)

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Name of the GeM+ entry: N. of cycles
Name of the REL file key: (it is not saved in the REL file, it is dynamically deduced)

Description and considerations: Number of cycles. This key only applies ot arc files (in ARC format) that have been cycled to generate polygon files (in POL format).

The key corresponds to the "Nr Ciclats" entry in the older documentation files. Although this information is given by GeM+ it is not stored in the REL file, rather it is calculated from the maximum value of the cycled key.

Follows the proposal of: GeM+

Obligatory according to GeM+: It is dynamically deduced

Cardinality: 1

Key type: N

AppliesToLayer: Yes
AppliesToSeries: No (includes information on the layer)

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Name of the GeM+ entry: Cycles
Name of the REL file key: ciclat#

Description and considerations: The name and address of the polygon file or files cycled over the vector arcs. In GeM+ the absolute address is saved whereas the REL file stores the relative address. This key only applies ot arc files (in ARC format) that have been cycled to generate polygon files (in POL format). It corresponds to the key with the same name in the older documentation files.

Follows the proposal of: GeM+

Obligatory according to GeM+: No

Cardinality: N

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (contains information about the layer)

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Name of the GeM+ entry: Arc Source
Name of the REL file key: ArcSource

Description and considerations: The name and address of the arc file (in ARC format) over which the polygons (in a POL format file) have been cycled. In GeM+ the absolute address is saved whereas the REL file stores the relative address. This key only applies to polygon files in POL format. It corresponds to the key with the same name in the older documentation files.

Follows the proposal of: GeM+

Obligatory according to GeM+: Yes

Cardinality: 1

Key type: C

AppliesToLayer: Yes
AppliesToSeries: No (contains information about the layer)

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