Pitney Bowes MapInfo Vertical Mapper - Manual (Page 136)

The Point-to-Point Visibility Function
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Vertical Mapper 3.7
The Grid list enables you to select the appropriate open grid file for analysis if such selection is not
made in the Grid Manager.
The Viewing Parameters section enables you to control the intervisibility calculation for each
endpoint of the line.
You can enter x- and y-coordinates as well as an offset height above the surface at both the Looking
From and the Looking To viewpoint positions. This section enables you to add a value to the From
point that represents, for example, the height of a transmission tower. Similarly, a height value may
be added to the To site that represents, for example, the height of a receiver.
If you are trying to measure line of sight from a transmitting antenna to a receiving car antenna, you
may want to add a value of 120 metres to the From point to represent the height of the transmission
tower, and add 1.5 metres to the To point to represent the approximate the height of the car antenna
above the surface of the ground.
The Earth Curvature Model list enables you to choose an earth curvature model. Earth curvature
must be taken into account for most line of sight calculations. You can select one of the following
models:
Normal Earth Curvature calculated using an oblate spheroid model.
4/3 Earth Curvature allows radio frequency engineers to model the slight curvature of a radio
wave as it travels over the earth’s surface due to diffraction effects.
No Earth Curvature ignores earth curvature
The Number of Samples box enables you to control the number of points along the line of sight
from which the intervisibility calculation is made and, therefore, the number of points that will be
plotted in the line of sight graph.
A value of 100 is considered appropriate for most calculations; however, the greater this value, the
more detail is added to the graphed profile.
The Create Results Table check box enables you to save all of the graphed information to a
MapInfo table, which can be viewed in a Browser window.
The resulting table contains five columns with the following information.
• The Distance value is the distance measured from the viewing location to the sample location.
The sample location is the location along the viewing line where the grid was analysed. By
default this line is sampled 100 times. However, it can be modified in the Point-to-Point dialog
box.
• The Viewable Elevation value is the elevation at the sampled location that can be seen from the
viewing point. All values are based on the “no earth curvature” model, and they are not displayed
in the graph window.