3/29/2024 0 Comments Edit oddysey bin fileTo control the distortion inherent in a rectangular projection, limits are set on the valid area of projection. The D and P buttons show the specific datum and projection parameters. On other projections, such as the Universal Transverse Mercator projection, the user must explicitly set the datum. If the datum contains multiple regions, the user must set the region. Many projections such as the British National Grid or the Swiss National System are unique and when one of these categories are selected, the corresponding datum will be automatically set. The projections are loosely organized alphabetically. In other words there are no rectangular x, y values. In the Pathloss program, the projection category “Geographic” means latitude and longitude. The rectangular format is required to display geographic information on a flat surface. Therefore, in the case of local datums, the user needs to specify the specific region for the datum.Ī projection converts coordinates between spherical (geographic latitude and longitude) values and rectangular x, y values. Each region has its own transformation parameters. In order to improve the transformation accuracy, the overall area of the datum may be divided up into smaller regions. Parameters to transform coordinates between this datum and the WGS 1984 datum.These are used in the great circle arc distance calculations. The datum definition contains the following information: Several examples of these errors are given in the table below. The errors between coordinates expressed in different geocentric datums (e.g NAD83 and WGS84) are not significant however, serious positional errors can occur if the coordinates belonging to a local datum are used in a geocentric datum or vice versa. For example, the reference point for the North American datum of 1927 (NAD27) is a triangulation station at Meades Ranch in Kansas. The reference point for a local datum will be some monument in the area. The reference point for geocentric datums is the mass center of the earth. Basically there are two types of datums: local or geodetic and geocentric. Conversely, the same location in different datums will have different coordinates. The same coordinates in different datums will point to different locations. DatumĪ datum is a horizontal reference used to specify latitude and longitude coordinates. The following paragraphs provide a brief description of these terms as they are used in the Pathloss program. In other cases, the user must set these parameters and therefore, an understanding of these terms is necessary. For example, when an SRTM digital elevation model is selected, the datum is set to WGS84 and the projection to geographic. Some of these will be automatically set by the program. Datum and Projection DefinitionĮach of the tabs in the GIS setup include a datum and projection definition. When the network display file is loaded, the associated p6g file will be automatically loaded. The network display file (gr5 file) includes the full path name of the p6g file. The file name should reflect the geographic area and possibly the specific data formats used in the file. Click the GIS files button to access the files menu. The GIS settings are saved in a file with the suffix *.p6g. The setup procedure is organized in seven tabs. Backdrop imagery - (Ortho photos, Scanned imagery, Maps).Terrain clutter database to add clutter to terrain profiles and for clutter backdrops.Digital elevation models (DEM) for terrain profile generation and elevation backdrops.This dialog defines the following components of the Pathloss program’s geographic information settings: Select the Configure-Set System-GIS Setup Dialog from the menu. These datasets are labeled LEGACY, and the user should consider using more current higher resolution datasets. Some data sources are no longer available but have been included in the documentation for users wanting to work with these legacy datasets. The scope of this help section is to guide the user in setting up a manual GIS Configuration. Pathloss 6 has many new features for managing terrain data automatically, but there may be cases where users are working with terrain data outside of the automatic sources.
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