Overview
The GIS configuration controls the following aspects of the network display:
· specifies the datum and projection of the site coordinates. All site coordinates must be referenced to the specified datum
· primary and secondary terrain database definition
· clutter 1 and clutter 2 database definition
· backdrop imagery definition
· vector data definition.
The GIS configuration is saved in a file with the suffix p5g. Furthermore, the full path of this GIS file name is saved in the network display gr5 file. When a network gr5 file is loaded, the corresponding GIS file is automatically loaded at the same time
On a new project, any existing GIS p5g file can be loaded. The GIS configuration can be set to load a default p5g file on start-up. Wen a network gr5 file is opened the GIS configuration will be reset to the p5g file specified in the network.
The GIS configuration in the PL50L (standalone) program includes its own GIS configuration. Backdrop imagery and and vector data are not defined in this application. The same p5g files are used with both the PL50 and the PL50L application. In the PL50L (standalone) program the datum and projection will be reset to thedatum and projection defined in the pl5 file when it is loaded.
Select Configure - Set GIS configuration to access the GIS setup dialog. Note that this dialog has a files menu. The setup is organized in the following tabs: site coordinates, primary DEM, secondary DEM, Clutter 1, Clutter 2, backdrop imagery and vector data. In the PL50L standalone application, the last two tabs are not shown.
Datum - projection definition
The ideal GIS configuration occurs when all of the GIS components (sites DEM, clutter, backdrop imagery and vector data) are referenced to the same datum - projection. This is the situation in Planet data sets; however in many cases the available data in the GIS components may be in a different datum - projection. A typical example would be NED data in NAD83 (latitude-longitude) and orthophoto
imagery referenced to state plane coordinates. To deal with this situation each of the GIS tabs has its own datum - projection setting.
These are organized alphabetically in terms of a general projection category and the specific projection. 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. On other projections, such as the Universal Transverse Mercator projection, the user must set the datum.
A special projection category is the Geographic projection. This means that the coordinates are in latitude and longitude only. A rectangular projections is not used. The user must set the datum in this case.
Note that the geographic coordinates latitude and longitude are always present. Distance and azimuth calculations use latitude and longitude. Path profiles are created by calculating the points along the path which follow a great circle are between sites. Using the special geographic projection, it is possible to have only the latitude and longitude. If any other projection is specified, both the latitude - longitude and the projected coordinates are specified.
Some projections categories are classed as fixed or variable. These are
· Australian map grid AGD 66 fixed zone or variable zone
· Australian map grid AGD 84 fixed zone or variable zone
· Map grid of Australia MGA 94 fixed zone or variable zone
· Universal transverse Mercator (UTM) fixed zone or variable zone
· Gauss confrom - South Africa - fixed meridian or variable meridian
Geographic data can be specified in either latitude- longitude or in projected coordinates. If a variable zone is selected, in a UTM projection, then the following operation will be in effect:
· If latitude - longitude are entered, the corresponding easting, northing and UTM zone will be calculated.
· To enter the projected coordinates, the easting northing and the UTM zone must be entered to calculate the corresponding latitude
If a fixed zone is selected, in a UTM projection, then specific zone must be specified. The following operation will be in effect:
· If latitude - longitude are entered, the corresponding easting, northing for the specified UTM zone will be calculated.
· To enter the projected coordinates, only the easting and northing must be entered to calculate the corresponding latitude. The fixed zone specified
The use of variable zone definitions in terrain elevation and clutter databases has other implications which are described in these specific sections.
A datum includes the parameters to transform coordinates to and from the WGS84 datum. On regional datums which cover a large geographic area, the datum can include a number of regions with specific transformation parameters for that region. In these case the user must also set the specific region.
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