FEI Horizon Calculator

---

Inputs

Observation Height	h= inches feet miles millimeters meters kilometers
Object Distance	o= inches feet miles millimeters meters kilometers as  tangent (level from observer) curve (great circle distance)
Earth Radius	R= inches feet miles millimeters meters kilometers ϕ= latitude°    Refraction( 0 %) *
Image Width	w= px
Horizontal FOV	fov= °

  

---

Help  |  permanant link  🔗

Calculations

value	formula	in	ft	mi	mm	m	km
Horizon† *	d=sqrt(h(h+2×R))	horizon	horizon	horizon	horizon	horizon	horizon
Surveyor Drop†	Dₛ=8"×o²	dropₛ	dropₛ	dropₛ	dropₛ	dropₛ	dropₛ
Drop†	D=R/cos(o/R)-R	drop	drop	drop	drop	drop	drop
Obscured† *	x=sqrt((o-d)²+R²)-R	obscured	obscured	obscured	obscured	obscured	obscured

value	formula	radians	degrees	DMS
Tilt ∠	t=o/R	tilt	tilt	tilt
Dip ∠ *	a=atan(d/R)	dip	dip	dip
Angular Size	α=2*atan(h/o/2)	α	α	α

value	formula	pixels
Sagitta, horizon centered	w*(H*cos(a)-(Z*cos(fov/2)*sin(a))/(2*Z*sin(fov/2))	sag
Sagitta, camera level	w*d/R*tan(fov/4)/2	sag

Requires HTML5 Canvas Support
Bug Report / Discussion Page

NOTES (v0.0.6):
Calculations assume equal elevation terrain, clear line of sight, sane input values.