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Wasmer Consulting NMPlot User's Guide Introduction to the Noise Model Grid Format
The Noise Model Grid Format (NMGF) is a well-documented standard way of representing a grid and its auxiliary information.
Internally, NMPlot processes all grids using NMGF, as shown in the Details pane of the Grid Document window.
The NMGF standard includes a format for storing grids in files. Many third-party applications communicate with NMPlot using NMGF grid files. Writing a NMGF file is the easiest ways to import third-party data into NMPlot. For a quick-start guide to creating NMGF files for this purpose, see Quick-Start Guide to Importing Data into NMPlot.
This appendix provides an overview of the NMGF standard. Complete documentation is available from the NMGF web page, http://www.wasmerconsulting.com/nmgf.htm.
There are a number of computer models in use that calculate the noise impacts of installations, such as airports and railroads, upon the surrounding community. Examples of such models include the United States Air Force's (USAF) NOISEMAP and the United States Federal Aviation Administration's (US FAA) Integrated Noise Model (INM).
In the early 1990's, each model defined its own output file format. This resulted in duplicate effort developing post-processing utilities that performed essentially the same tasks. For example, both the USAF and the US FAA independently developed contour plotting utilities for use with their respective noise models.
To promote the development of shared post-processing utilities, the USAF and the US FAA sponsored the development of a standard grid file format that met the needs of both models. This format is known as the Noise Model Grid Format (NMGF). Version 1.0 of this format was released in September 1993.
While NMGF was originally developed to support noise models, it is neutral to any particular application domain. A NMGF grid can just as easily contain data from other types of models (for example, air pollution models) or from sources other than computer models (for example, measured data).
Data is stored in the NMGF format as a list of sections. There are more than 30 types of sections, each with a specific purpose. For example, a CART section defines a coordinate system used to specify geographic locations in a grid.
Section types are defined that specify data points (both on rectangular grids and as lists of location-value pairs), information about data points (the physical units, the range of valid data point values, etc.), geographic annotations (for example, the locations of roads and buildings), and bookkeeping information (where the data came from, who created the data, etc.).
The NMGF data structure is hierarchical. That is, sections can have subsections, called child sections. A child section specifies an attributes of its parent section.
As an example, consider the ZCRD section, which specifies an altitude or height. A ZCRD section by itself is meaningless: you do not know what the altitude refers to. The ZCRD section is always used as a child of the section it refers to.
Consider the PNTS section, which specifies information about a point geographic feature (for example, the location of a house). This section has several required parameters, such as the geographic coordinates of the point. The altitude of the point is not a required parameter. However, the ZCRD section can optionally appear as a child of the PNTS section to specify the altitude of the point.
This NMGF section defines a geographic coordinate system used to specify locations in the grid. If a grid does not contain a CART or UTMC section, longitude and latitude are assumed.
CART - Define a local flat-Earth Cartesian coordinate system for specifying geographic coordinates
UTMC - Define a Universal Transverse Mecator (UTM) coordinate system for specifying geographic coordinates
These NMGF sections specify information about the data points in a grid.
DAPY - Specify the grid's defined area polygon: i.e., the geographic area where data is known. See Defined Area Polygon.
DPAL - Specify a group of data points as a list of location-value pairs.
GRID - Specify a group of data point arranged on a regular rectangular grid
GTSH - Specify the range of data point values that is considered valid
MTRC - Specify what is being measured by the data points, and what units of measurement are used
SUBG - Specify a nested subgrid: i.e., a set of data points that doubles the resolution of a portion of a grid
These NMGF sections specify map data stored in a grid.
AREM - Define a geographic feature consisting of one or more closed polygons
ARES - Define a geographic feature consisting of a single closed polygon
BKMP - Define information about a background map that is stored in an external file
LINC - Define a geographic feature consisting of a series of (possibly non-contiguous) lines and arcs, described by a series of commands that move a hypothetical cursor
LINM - Define a geographic feature consisting of one or more continuous lines
LINS - Define a geographic feature consisting of a single continuous line
PNTM - Define a geographic feature consisting of one or more points
PNTS - Define a geographic feature consisting of a single point
This NMGF section is used to record the creation and modification history of a grid.
SORC - Specify audit trail information about a grid: how, why, when, where, and by whom it was created
These NMGF sections allow predefined optional attributes to be specified. They are used only as child sections.
DATE - Specify a date
DESL - Specify a detailed multiple-line description of an object
DESS - Specify the proper name or a short one-line description of an object
HEAD - Specify the direction (i.e., the heading) of an object
PERS - Specify information about a person: name, telephone number, etc.
PROG - Specify the name and version of a computer program
TIME - Specify a time
WARN - Specify a problem or limitation of the data in a NMGF grid
ZCRD - Specify the height or altitude of an object
These NMGF sections allow grids to store information that was not anticipated by the designers of the NMGF format: arbitrary attributes can be specified as name-value pairs. These sections are used only as child sections.
ATRC - Specify a coordinate as an arbitrary attribute of a NMGF section
ATRF - Specify a floating point number as an arbitrary attribute of a NMGF section
ATRI - Specify an integer as an arbitrary attribute of a NMGF section
ATRS - Specify text as an arbitrary attribute of a NMGF section
ATRT - Specify a table of information as an attribute of a NMGF section
These NMGF sections control the processing of a NMGF grid when it is stored in a file.
ENDF - Mark the end of a NMGF grid file
TITL - Mark the beginning of a NMGF grid file, and specify the NMGF version number
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