Using information from the CASUALTY
There are times that the casualty cannot give an exact location, but can give a bearing from where it is to a recognised point.
Most often, the bearing will be given as a magnetic bearing from a compass, but it is vital that we find out what device the bearing was taken on.
As with the LKP using bearings from an observer(s), we can calculate an estimated position from
•one bearing and a distance to one point
•two or three bearings to two or three points
One point
This will give the least accurate LKP because the casualty will have to estimate the distance from where they are to the point, but it WILL give a rough idea.
•A : This allows the user to tell SearchWell how many points will be used
•B : This indicates whether the bearings are True or Magnetic .... if there are more than one points and there are different bearing types (True and Magnetic) then the bearings must
be converted to either True or Magnetic before entering the value.
When Magnetic is selected, the Magnetic variation for the default station will be displayed. Either the station can be changed or the variation can be changed as necessary.
•C : If the point is found in the Points Table, it is quicker to use a filter to select out just those points that have the filter value in their name. When using this, type the word you require and then PRESS ENTER
•D : This has the list of Points from the Points table. If a filter has been used, it will show the filtered points.
When you click on a point here, the coordinates of the point will be displayed in the Coordinates box.
•E : This is where the user can type coordinates if the position is not taken from the Points table, or, if it is taken from the Points table the coordinates of the point will display here
•F : The bearing in degrees from the casualty to the point. The bearing must be the same as that specified in "B" .... if Magnetic is selected, the given bearing must be Magnetic
•G : This only displays if One point is selected in "A" .... if more than one point is going to be given the distance box is hidden. The input must be distance from the casualty to the point in nautical miles.
•H : Click on this CALCULATE button to perform the calculation once all the input information has been given
•I : Click on this CLEAR button to clear the screen and any previous calculation results
•J : Clicking on this HELP button will display a box with the help information for the screen
•K : The coordinates of the calculated LKP. These are shown in the formats Decimal Degrees, Degrees and Decimal Minutes, Degrees Minutes and Seconds
•L : This block gives information about the Point
oDistance to the casualty from the point in nautical miles
oBearing from the point to the casualty. This will be close to the reciprocal of the bearing given to us by the casualty - if the casualty sees the point on a true bearing of 90°, then the bearing from the point to the casualty will be 90° + 180° = 270°. As there will be a margin of error, when there is more than one point, the bearing from the point to the casualty is unlikely to be exactly 180° different.
•M : GPX button which, when clicked, will create a waypoint of the LKP position that can be sent to the rescue vessel so that they can easily navigate to the LKP
•N : User Manual - clicking on this button will take you to the LKP section of the user manual which is stored on the internet
•O : Google Earth button which opens Google Earth when clicked
•P : Exit button - clicking on this button will close the LKP form. It is important to note that all the information displayed on the form will be lost
Two points
The form for when the casualty can give us the bearing to 2 points -
When the Two points button is selected, space for two inputs is displayed and the input for distance is removed
The LKP is taken as the point at which the two lines cross.
Three points
If the user selects 3 points the form will display as follows -
You can see that there is input space for three different callers, and the display shows information about all three callers.
The calculation
This time the three lines intersect each other forming a triangle called a "cocked hat". The coordinates in the centre of the triangle are taken as the LKP coordinates
This will tend to be the most accurate calculated LKP.
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