NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Correction factors for eye distortion
From: Bill B
Date: 2006 Jul 19, 19:16 -0500
Testing is still in the works, but let's get back to the original question:
"More to the point, is there some way to mathematically null out the eyeball
problem... using a sphere (sun or moon) and a natural (flat
line) horizon with my left eye?"
Let's set up a hypothetical situation.
Sun SD 15.8', diameter 31.6', 4SD 63.2'
IE from horizon 0.0'
----------------------------
Horizontal Readings
Reading on the arc 31.3'
Off the arc 31.5' (60 - 28.5 direct reading)
IE from horizontal observations of sun, 0.1 off the arc
Observed 4SD 62.8'
---------------------------------
Vertical readings
Reading on the arc 32.0'
Reading off the arc 31.8' (60 - 28.2 direct reading)
IE from vertical observations of sun, 0.1 on the arc
Observed 4 SD 63.8'
-----------------------------------------
Regarding a correction factor for IE determined from horizontal sun
observations, it appears simple.
Correction factor = horizon IC - horizontal sun IC
Correcting to natural horizon IC: Sun IC - correction factor = horizon IC.
Correcting for the vertical distortion seems a bit more problematic. If the
on-the-arc reading is 0.4 over ideal, one might say that represents the
cumulative overage from two images, so divide it by two for one image
tangent to a linear image.
That assumes the distortion is symmetrical. In my case the left eye
distortion looks more like an egg tilted 10d clockwise, with the pointy end
up. Who is to say, without a medical or academic doctorate and sophisticated
at his/her disposal, that most (or all) of the distortion does not occur on
the upper or lower limb?
What, other than the old-bold empiricist approach, averaging a ton of
observation averages, can I do to determine a personal correction factor?
Personal error (bias) is often spoken of in cel nav texts as well as
helmsman bias in other texts, but no method is given to determine the bias.
Bill
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From: Bill B
Date: 2006 Jul 19, 19:16 -0500
Testing is still in the works, but let's get back to the original question:
"More to the point, is there some way to mathematically null out the eyeball
problem... using a sphere (sun or moon) and a natural (flat
line) horizon with my left eye?"
Let's set up a hypothetical situation.
Sun SD 15.8', diameter 31.6', 4SD 63.2'
IE from horizon 0.0'
----------------------------
Horizontal Readings
Reading on the arc 31.3'
Off the arc 31.5' (60 - 28.5 direct reading)
IE from horizontal observations of sun, 0.1 off the arc
Observed 4SD 62.8'
---------------------------------
Vertical readings
Reading on the arc 32.0'
Reading off the arc 31.8' (60 - 28.2 direct reading)
IE from vertical observations of sun, 0.1 on the arc
Observed 4 SD 63.8'
-----------------------------------------
Regarding a correction factor for IE determined from horizontal sun
observations, it appears simple.
Correction factor = horizon IC - horizontal sun IC
Correcting to natural horizon IC: Sun IC - correction factor = horizon IC.
Correcting for the vertical distortion seems a bit more problematic. If the
on-the-arc reading is 0.4 over ideal, one might say that represents the
cumulative overage from two images, so divide it by two for one image
tangent to a linear image.
That assumes the distortion is symmetrical. In my case the left eye
distortion looks more like an egg tilted 10d clockwise, with the pointy end
up. Who is to say, without a medical or academic doctorate and sophisticated
at his/her disposal, that most (or all) of the distortion does not occur on
the upper or lower limb?
What, other than the old-bold empiricist approach, averaging a ton of
observation averages, can I do to determine a personal correction factor?
Personal error (bias) is often spoken of in cel nav texts as well as
helmsman bias in other texts, but no method is given to determine the bias.
Bill
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---
