A question for you surveyors
- Thread starter GrantMO
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patrickg
Veteran Member
Egon, Your statement, "...the size of the building would have to be approaching zero for
the curvature to not have any effect", uses the word A N Y which is an absolute like all or no and makes strict interpretations whereas in Grant's original problem statement, "How big of a building would it take before you started to have to adjust the level to the earth's curvature?", although worded loosely, implies, where does the effect become significant. Of course taken literally, "to have to adjust" could imply, perhaps erroneously, that at some point code compliance or some other legality "kicks in". You don't HAVE to adjust at all even with a 10 mile long building but you better have a robust rebar schedule in the slab or tollerate having the cener of the floor 20 inches below grade.
In actual practice the variations in the surface of a building site are much larger than the effect of the curvature of the earth, even for mile long buildings unless you are building somewhere like the Bonneville salt flats.
Patrick
the curvature to not have any effect", uses the word A N Y which is an absolute like all or no and makes strict interpretations whereas in Grant's original problem statement, "How big of a building would it take before you started to have to adjust the level to the earth's curvature?", although worded loosely, implies, where does the effect become significant. Of course taken literally, "to have to adjust" could imply, perhaps erroneously, that at some point code compliance or some other legality "kicks in". You don't HAVE to adjust at all even with a 10 mile long building but you better have a robust rebar schedule in the slab or tollerate having the cener of the floor 20 inches below grade.
In actual practice the variations in the surface of a building site are much larger than the effect of the curvature of the earth, even for mile long buildings unless you are building somewhere like the Bonneville salt flats.
Patrick
patrickg
Veteran Member
Nah, the floors arent level enough for me.
Egon
Epic Contributor
Patrick:
Every time you move your leveling device, no matter how little, you have adjusted to the curvature of the earth.
Egon
Every time you move your leveling device, no matter how little, you have adjusted to the curvature of the earth.
Egon
MossRoad
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That's why you have to take all of your measurements from the same reference point and hope that your measuring device is accurate to +- 1/4 inch in a mile. Heck, I was impressed when my garage foundation came out to +- 1/4 inch in 32 feet /w3tcompact/icons/laugh.gif. At that rate, if I build a mile long building, I could come out over 40" off at the other end.
patrickg
Veteran Member
Egon,
I don't know how to appropriately respond to your "profound" statement (proof to follow). I thought that gravity being what it was pretty much pointed leveling devices (gravity oriented ones) radially inward toward the center of the earth(better stated, center of gravity), +/- any local anomalies that effect which way is down (or up). If the earth were radially homogenous and a sphere, straight down would always be radially inward. In the real world there are variations in density that curve the gravitational field. Consider the base of a large mountain and how it would "bend" the local "up/down" a bit out of line with normal to the tangent plane.
If you chose to, you could use non gravitationally based instrumentation to determine a plane tangent to the curvature of the earth which would define level at that location. Consider optically based devices with averaging techniques. These would, of course, not do too well in highly irregular terrain. Space based systems supported by orbiting satellites such as the GPS system with its constellation of NAVSTAR
(NAVigation Satellite Timing and Ranging) satellites permit users to determine their position in three
dimensions anywhere on the earth. The third dimension being altitude allows a user to determine the altitude at differing locations and define a flat plane (large slab, runway, whatever), if you choose, without traditional gravity referenced instruments like spirit levels. Once a plane has been defined optical instrumentation such as LASERs and transits (referenced to defined plane not a plumb bob or spirit level) can be used to "work" the site.
Actually your statement, "Every time you move your leveling device, no matter how little, you have adjusted to the
curvature of the earth." is not accurate in the real world where the earth is not a true sphere and its gravitational mass is not homogenous. In fact when you move your "device" you readjust to the "new" local gravity vector's direction which is often not consistent with the local shape (curvature) of the earth.
Thngs often get complicated beyond everyday experience when viewed in detail. Recall the Einstein quote, "everything should be made as simple as possible but no simpler." Oversimplification (at the opposite end of the spectrum from our progression) destroys reality while too much detail can hide the fundamentals. "Aye, there is the rub", with appologies to the knoble bard.
Patrick
P.S. Where do you stand on the issue of the distance travelled as the thickness of the catepillar treads is increased?
I don't know how to appropriately respond to your "profound" statement (proof to follow). I thought that gravity being what it was pretty much pointed leveling devices (gravity oriented ones) radially inward toward the center of the earth(better stated, center of gravity), +/- any local anomalies that effect which way is down (or up). If the earth were radially homogenous and a sphere, straight down would always be radially inward. In the real world there are variations in density that curve the gravitational field. Consider the base of a large mountain and how it would "bend" the local "up/down" a bit out of line with normal to the tangent plane.
If you chose to, you could use non gravitationally based instrumentation to determine a plane tangent to the curvature of the earth which would define level at that location. Consider optically based devices with averaging techniques. These would, of course, not do too well in highly irregular terrain. Space based systems supported by orbiting satellites such as the GPS system with its constellation of NAVSTAR
(NAVigation Satellite Timing and Ranging) satellites permit users to determine their position in three
dimensions anywhere on the earth. The third dimension being altitude allows a user to determine the altitude at differing locations and define a flat plane (large slab, runway, whatever), if you choose, without traditional gravity referenced instruments like spirit levels. Once a plane has been defined optical instrumentation such as LASERs and transits (referenced to defined plane not a plumb bob or spirit level) can be used to "work" the site.
Actually your statement, "Every time you move your leveling device, no matter how little, you have adjusted to the
curvature of the earth." is not accurate in the real world where the earth is not a true sphere and its gravitational mass is not homogenous. In fact when you move your "device" you readjust to the "new" local gravity vector's direction which is often not consistent with the local shape (curvature) of the earth.
Thngs often get complicated beyond everyday experience when viewed in detail. Recall the Einstein quote, "everything should be made as simple as possible but no simpler." Oversimplification (at the opposite end of the spectrum from our progression) destroys reality while too much detail can hide the fundamentals. "Aye, there is the rub", with appologies to the knoble bard.
Patrick
P.S. Where do you stand on the issue of the distance travelled as the thickness of the catepillar treads is increased?
Egon
Epic Contributor
MossRoad:
Them +/- just naturally cancell each other out and you end up right on.
Wish I could get a foundation that close.
Egon
Them +/- just naturally cancell each other out and you end up right on.
Wish I could get a foundation that close.
Egon
Egon
Epic Contributor
Patrick:
Yes mass does attract mass but then there is also an issue of what has mass and what can be bent and by how much and how does speed affect all this.
There are an infinite number of radii from the center of earths mass to the surface.
Will a person standing at the end of a three mile runway defined as level from orbiting devices be completly visible to another person at the other end of the runway?
As for those cat threads; if they are getting thicker its probably going to go faster or be standing still as its picking up good sticky clay and sitting in place spinning in it's tracks.
Egon
Yes mass does attract mass but then there is also an issue of what has mass and what can be bent and by how much and how does speed affect all this.
There are an infinite number of radii from the center of earths mass to the surface.
Will a person standing at the end of a three mile runway defined as level from orbiting devices be completly visible to another person at the other end of the runway?
As for those cat threads; if they are getting thicker its probably going to go faster or be standing still as its picking up good sticky clay and sitting in place spinning in it's tracks.
Egon
patrickg
Veteran Member
Egon, I'll number its parts and comment on your post, "by the numbers."
1. Yes mass does attract mass but then there is also an issue of what has mass and what
can be bent and by how much and how does speed affect all this.
2 There are an infinite number of radii from the center of earths mass to the surface.
3. Will a person standing at the end of a three mile runway defined as level from orbiting
devices be completly visible to another person at the other end of the runway?
4. As for those cat threads; if they are getting thicker its probably going to go faster or be
standing still as its picking up good sticky clay and sitting in place spinning in it's tracks
1. Most surveyors I have seen aren't going fast enough while working to make either the general or special theories of relativity needed, much less the Grand Unified Theory of everything.
2. Yeah, so?
3. For most practical purposes yes. Wanna get real picky, then no, unless the other person turns around, his "other" side is not visible as of course internal organs etc are probably not visible. Depends on what you mean by "visible". I hate it when I sound Clintonian!!!!!! ARGHHHHHHH!!!!!!!!!! At least you could see where the pavement met his shoes (feet or ???) and continuously up to his head and beyond except for any mirage type phenomena due to heating of the air in contact with the runway which might obscure a clear view of his lower portions.
4. Thanks for agreeing with my preciously strongly defended position (less the stuck in the mud part.
Patrick (looking for a vortex pump requiring no more than 39 HP and suitable for 3PH mounting and PTO driving, albeit with a step up belting arrangement to get in the 2000 to 4000 RPM range (whatever speed draws no more than 39 HP)
1. Yes mass does attract mass but then there is also an issue of what has mass and what
can be bent and by how much and how does speed affect all this.
2 There are an infinite number of radii from the center of earths mass to the surface.
3. Will a person standing at the end of a three mile runway defined as level from orbiting
devices be completly visible to another person at the other end of the runway?
4. As for those cat threads; if they are getting thicker its probably going to go faster or be
standing still as its picking up good sticky clay and sitting in place spinning in it's tracks
1. Most surveyors I have seen aren't going fast enough while working to make either the general or special theories of relativity needed, much less the Grand Unified Theory of everything.
2. Yeah, so?
3. For most practical purposes yes. Wanna get real picky, then no, unless the other person turns around, his "other" side is not visible as of course internal organs etc are probably not visible. Depends on what you mean by "visible". I hate it when I sound Clintonian!!!!!! ARGHHHHHHH!!!!!!!!!! At least you could see where the pavement met his shoes (feet or ???) and continuously up to his head and beyond except for any mirage type phenomena due to heating of the air in contact with the runway which might obscure a clear view of his lower portions.
4. Thanks for agreeing with my preciously strongly defended position (less the stuck in the mud part.
Patrick (looking for a vortex pump requiring no more than 39 HP and suitable for 3PH mounting and PTO driving, albeit with a step up belting arrangement to get in the 2000 to 4000 RPM range (whatever speed draws no more than 39 HP)
Will
Gold Member
Here is an accurate way to approximate this sort of thing:x = height above earth's surface (measured in feet)y = distance to horizon (measured in miles) as seen from a point at height x above the earth's surfacey = square root(3x/2)So a 6' tall man can see points on the earth's surface up to square root (18/2) = 3 miles. Conversely, a laser beam tangent to the earth will be 6' off the ground after 3 miles.It's unusual to have a formula where you stick in one unit (feet) and get out another unit (miles). The thing that makes it work is that the earth's radius in miles (3960) is exactly 3/4 of the number of feet in a mile.