7.2 Calculating Visible Area Map (2)

(1) Preparation of Elevation Data

Prepare the elevation data covering the area for the visible area map.
The map must cover from the mountain in the center to the end of the area to be calculated. If some areas between are not covered by the map these parts are treated as the see. This may cause wrong visibility which should be invisible in the reality.
The digital map 250m grid (Elevation) of the Geographic Survey Institute Japan provides enough quality for the normal use. For more precise calculation 50m grid provides more detail calculation result but needs much time.
Further maps are also available for example; USGS 30 arc second demdcw, Free digital map (250m/1km) which are contained in the FYAMAP CD-ROM. These maps provide wide areas but with less quality.
(2) Preparation for Calculation
If you calculate for a mountain with known name Place Name Database will help you.
The setup for the calculation will be done only by giving the name of the mountain. For the displaying of the calculated visible area map the names will also be shown.

It is also possible to calculate for the point on the map pointed by the mouse.
Click the right mouse button on the point and select [Visible Area Map] - [Center]. If there is a place name available put the mouse pointer on it so that it is focused on. Then click the right mouse button. This enables you an exact placement of the center based on the place name data.

(3) Calculation Setting
Select [Tools] - [Visible Area Map] - [Calculation Option].
Input the name, the position, and the altitude of the mountain to be calculated as the center. When you use the mouse for (2) you do not have to enter these values.
If the place name data base is opened specify the name of the mountain from the list box on the left side. This enables an automatic input of the position of the mountain.
Type the first character on the list box. The list is scrolled automatically till the mountain with this first character appears.

Then specify the area to be calculated in km.

At last the quality has to be specified. Please refer to (4) of the last page for detail about the quality. If you calculate only a part of the map the quality has to be specified here.

After these settings click Ok button.

(4) Calculate for only specified area
To calculate for the only specified area select the area with mouse.
Put the mouse pointer on the top left corner of the area to be calculated on the map then click the right mouse button. Select [Visible Area Map] - [Region] then click the right mouse button on the bottom right corner of the area to be calculated on the map.
Then you will ba asked about the quality of the calculation, enter the values
When the visibility data file is open and even there is a prt already calculated this part will be calculated again.
(5) Stop Calculation
To stop the calculation select [Tools] - [Visible Area Map] - [Stop/Pause Calculating].
When the calculation is broken the visible area map for the area already calculated will be displayed.
(6) Save Calculation Result
The calculated result can be saved as a "Visibility File".
Select [File] - [Save] - [Visible Area Map (VAM)].
Enter file name (normally it has .VAM extension).
Data file which contents "Visibility Data" has .VAM extension.

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