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Hi Jamie & All, Feb 10, 2007
After my previous reply I thought of an approach that requires only
a good compass (Silva Huntsman or equivalent) and features that can be
located on a map (including the house location) such as highway
intersections, or abrupt bends in highways, provided the visible object
can be seen from these two (preferably three) locations. It is
surprising how precisely compass direction can be measured with a
hand-held compass if you don't hurry.
Just draw the headings, after correction for declination, on a large
scale map. Where the two (preferably three for confidence) lines cross
is the location of the visible object and from map scale calculate
distance. Probably most precise if the two outside sight points and the
target approximate an equilateral triangle.
Don't carry an eversharp in shirt pocket to record the headings !
There is something about the metal at the upper end of an eversharp
(nickel perhaps) that drives my compass crazy. I learned this almost the
hard way when walking several miles cross-country to a small lake.
Fortunately the sun came out briefly several times early on.
Yt, DW
Jamie Simpson wrote:
> Peter
>
> Are you aware of a method of determining distance of a visible object
> other than actually measuring or using a transit?
>
> If I could do that I think I could figure it out mathematically. But
> I don't think it can be done.
>
>
> ----- Original Message ----- From: "Peter Payzant" <pce@accesswave.ca>
> To: <naturens@chebucto.ns.ca>
> Sent: Thursday, February 08, 2007 12:38 PM
> Subject: Re: [NatureNS] Determining Elevation
>
>
>> Hi, Jamie-
>>
>> Elevation measurements from GPS are significantly less accurate than
>> lat-long measurements. This is due in part to the geometry of the
>> situation, and in part due to the fact that the GPS system calculates
>> your distance from the centre of a sphere, and then applies a model
>> of the earth's surface to correct for the earth's radius at your
>> location. There are other sources of error as well.
>>
>> There's lots about this on the net of course. Until you understand
>> the nature of the errors it's probably not a good idea to put too
>> much faith in what the GPS receiver tells you for elevation.
>>
>> If you wanted to get a good result, you could rent a surveyor's level
>> and work your way up to your house from the nearest known accurate
>> elevation.
>>
>> Peter Payzant
>>
>>
>> --
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>> 2/7/2007 3:33 PM
>>
>>
>
>
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