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A standard for representing georeferenced data sets

Latest Version
Version 2.5
The NMGF standard is freely distributed. Any interested party may download, use, and redistribute the standard, and create programs that read and/or write NMGF files. The standard documentation, however, may not be modified.
ANSI C or C++ compiler to use the NMGF Library
Download NMGF Standard (192 KB)
This ZIP file contains the documentation for the NMGF standard, in both Microsoft Word 7.0 and RTF formats. It also contains the C and C++ source code for the NMGF Library, sample programs that use the library, and sample grid files. See the ReadMe file for additional information.
Download Additional Samples (9 KB)
This ZIP file contains sample programs illustrating how to write Noisemap .grd grid files, .fea feature files, and .top topography files. Noisemap is an airport noise model developed by the United States Air Force. While these files are intended for the developers of Noisemap, other developers may be interested in them, as they provide additional examples of the use of the NMGF Library.
In particular, TOPOSAMP.C provides an excellent example for someone who wants to use the NMGF Library to translate a simple 2-D grid into the NMGF format.
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More Information
Quick-start Guide

What Is NMGF?

NMGF is a standard file format used to store sets of georeferenced data points. These data sets, also know as grids, represent measurable quantities that vary with geographic location. Examples include predicted noise levels around an airport, monthly records of rainfall across a state, and water temperature measurements in a lake.

An NMGF file can contain information about one or more rectangular primary grids of data points. Each primary grid may have an arbitrary location (with respect to each other and the surface of the earth), size, and rotation angle. Where greater resolution is required, a subsection of a primary grid may be specified in greater detail through the use of nested subgrids. A subgrid can itself contain nested subgrids: thus, any desired resolution can be achieved at areas of particular interest. See the NMGF icon at the top of this page for a visual example.

NMGF files can also contain sets of data points with arbitrary locations, stored as lists of X,Y,C triplets.

NMGF is the standard output format for a number of environmental noise models, including the United States Air Force's Noisemap, the United States Federal Aviation Administration's Integrated Noise Model (INM), and the United States Army Construction Engineering Research Laboratories' (CERL) BNoise.

The NMPlot application, available at http://wasmerconsulting.com/nmplot.htm, can read an NMGF file and display the contents in a variety of ways, such as a contour plot and a color gradient plot. NMPlot can also perform various operations on NMGF files, such as adding, subtracting, and merging two files.

Why Was NMGF Developed?

There are currently 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 past, each model defined its own output file format, which resulted in much duplicate effort developing post-processing utilities that performed essentially the same operations. For example, both the USAF and the US FAA independently developed contour plotting utilities for use with their respective noise models.

Therefore, the USAF and the US FAA sponsored the development of a standard grid file format that met the needs of both noise models. This format is known as the Noise Model Grid Format (NMGF).

NMGF: Not Just For Environmental Noise Models

While the NMGF standard was originally designed to support noise models, it is neutral to any particular application domain. A NMGF file 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).

Writing an NMGF File Containing Your Data: A Quick-Start Guide

The NMGF format has two subtypes: a binary version (known as NMBGF) and an ASCII (or text-based) version (known as NMAGF). The two formats contain the same information, but differ in how it is stored in a file.

NMBGF binary files tend to be smaller, and take less time to read and write, but are also more difficult to work with, and are recommended only when efficiency concerns are paramount.

NMAGF ASCII grid files, on the other hand, are designed to be easy to create, and can be viewed and edited using a simple text editor. If you want to convert a data set into the NMGF format with the minimum amount of effort, you should use the NMAGF ASCII subtype. A quick-start tutorial is available on putting your data into the NMAGF format.

The NMGF Library

The NMGF standard package includes a library of C and C++ functions for writing NMGF files. The library consists of the following files:

File Name Description



Implementation of the ANSI C library for writing NMGF files.



Implementation of a C++ class wrapper for the ANSI C library.



An ANSI C program that demonstrates how to use the ANSI C library to write NMAGF and NMBGF files.



The NMAGF and NMBGF files written when sample.c is compiled and run.



A C++ program that demonstrates how to use the C++ library to write NMAGF and NMBGF files.



The NMAGF and NMBGF files written when samplecp.cpp is compiled and run.

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