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----------- START REFRACTION ----------------------
local get_refraction = function(obs, refObj)
--[[ Calculate the adjustment in altitude of a body due to atmosphric
refraction. This value varies over altitude, pressure and temperature.
Note: Default values for pressure and temperature are 1010 mBar and 10C
local my_atm_press = 980; -- mBar (user define parameter)
local my_temp = 20; -- degree Celsius (user define parameter)
R = 1.0 / math.tan(math.rad(elev + (7.31 / (elev + 4.4))));
R = R - (0.06 * math.sin (math.rad (14.7 * (R / 60.0) + 13.0)));
-- take into account of atm press and temp
R = R * ((1010 / my_atm_press) * (283.15 / (273.15 + my_temp)));
-- convert from arcminutes to degrees
R = math.abs(R/60.0);
-- no refraction when the elevation is less of zero
if elev < 0 then R = 0.000 end
-- Citation and code port from LIBNOVA, C++ astronomical library (SOURCEFORGE.net)
----------- END REFRACTION ------------------------
The code is a function called when the longlatBox is drawn and displayed with a new textlayout label. The refraction's value will be zero for elevations less than zero. Refraction behave (based on custom location's pressure and temperature) from a maximum for low bodies' elevations to a minimum for high bodies' elevations. Such value is added to the true elevation.
If someone wish to test the code, a zip with the improved compassBox.lua is here
Notice that I've put the labels in such a position, but nonetheless it can be as is it in the default file. Just fit the refraction's text string for you needs.