Way OT: Elevation survey with Transit Rod

allischalmers6 · Oct 21, 2014

I have been studying how to measure and read elevation using a transit and rod. Since I enjoy learning new things I was wondering how the curvature of the earth effects elevation readings and if there is an equation to facture into compensate for the curvature. Thanks.

Russ from MN · Oct 21, 2014

I just Googled it, and it's about 8 inches per mile, And I think you would have to factor that in to be accurate.
Along that topic, the minster told us in church Sun. that the nnalert knew that the earth was round way before the Christians! I have heard that some of the ancient architecture is built to the curve, I wonder if they used a hand level to set each stone, that would do that.

allischalmers6 · Oct 21, 2014

So I would subtract 8 inches per mile? I kinda figured somehow the transit-level would somehow naturally work around the curvature.

Dr. Walt · Oct 21, 2014

Jim Phelps · Oct 21, 2014

That is not really true, people knew the earth was round way before nnalert came along. The ancient Egyptians and later the Ancient Greeks had already proved that to be a fact.

JMOR · Oct 21, 2014

Don't think you need to "factor" in anything! You look along a straight horizontal line of sight with your transit & out there at your rod, you take a reading. That reading is the elevation of that point relative to your horizontal line of sight, including earth's curvature, valley, hill or whatever.

Dell (WA) · Oct 21, 2014

AC6........my Dad was a professional surveyor and occasionally, he'd "hire" me to be his "rod-man".

While most transits use an 8-power scope, occasionally they have a 12-power scope. Everytime he took a reading, the damm plumb-bob would start swinging in the wind. He'd haffta "swing" the transit 180-deg to make certain the transit was LEVEL. Hardest part of me being a rod-man was keeping the rod "STEADY". Most distances were 1/4-mile (660-ft) or less. Man, I HATED draggin' that metal chain 'cuz it was 8-links. (12-ft to link) And iff'n yer eyeballs are good enuff to read 8-inches in 1-mile, better hang a plumb-bob from yer pecker and hire out as a surveyor.......the hung Dell

BTW.......they do include curvature of the earth in land or property surveys; you just gotta read the neats and bounds. They are referenced to USGS "corners" (round BRASS spots) set in the ground

Meangreen · Oct 21, 2014

Depends. If you were measuring distance with a steel tape/chain then there is an equation you have to calculate based on temperature to determine stretch/shrinkage of the metal.

When shooting elevation with a transit & rod, you rock the rod to figure out the mean reading and then calculate elevation from that. Curvature of the earth wouldn't be an issue because you cannot accurately read a rod from that far of a distance.

Now days the transit and rod is used on lots, but not large surveys. You would use a total station that shoots a laser beam at a prism to shoot distance & elevation in one shot. Some of the units are robotic and the total station sits over a bench mark and one guy can walk around take all the shots he needs by himself. I believe the won't shoot more than 1/4 mile because accuracy is reduced the farther out from the base you are.

Other method is GPS, but that can be temperamental at times and it is used when you need to be a great distance from the base point since the GPS receiver with the man doesn't need a direct line of site to the base unit like the other methods mentioned.

EricInSEI · Oct 21, 2014

The Romans not only knew the earth was round, they knew how big the earth was and how far away the moon was. Mostly with basic geometry. Sailing ships disappear as they sail toward the horizon because of the earths curvature.

I would question your minister's credentials, he doesn't sound very educated.

mEl · Oct 21, 2014

Isaiah 40:22-----It is he that sitteth on the circle of the earth and the inhabitants thereof are as grasshoppers--------------KJV Bible written well over 2000 yrs ago.

Mel

Janicholson · Oct 21, 2014

Every station point is leveled to local gravity. Thus if a siting was a mile away (not seriously) the center of the line of site would be closer to the ground than the ends, but the elevation at each end would measure the same (assumes a billiard ball landscape) The highest spot in Indiana is in a field that is as flat as can be sensed by a person standing there. Jim

thurlow · Oct 21, 2014

Actually, it was written about 400 years ago.

bjb in TX from Ne · Oct 21, 2014

It actually has been worked out. If i recall from my survey course in Nebraska, the base unit is 36 sections (6 miles x 6 mile). One of the section (lower right maybe?) is actually not square and not a full 640 acres. This is where the error in the curvature of the earth has been accounted. If you find the USGS survey maps of the US (probably in a depository library) then you can find the main parallels and see the one section in every 6x6 section square is somewhat trapezoidal spaced.

sourgum · Oct 21, 2014

We were taught that many people thought Columbus would never be seen again and many sailors would not go with him because most people thought the world was flat at that time and he would sail off the edge and be gone. When he returned to Spain people realized the world might be round. That was only 522 yrs ago.

dpendzic · Oct 21, 2014

in my 40 years of civil engineering and designing and building bridges we never compensated for the earth curvature in our readings---how ever with modern day high power levels that can shoot a line a very long distance I believe they do--but the adjustment is well within the standard % of error.
so really insignificant

gene bender · Oct 21, 2014

1/4 mile is 1320ft

mEl · Oct 21, 2014

Thurlow, the KJV, I'll give you that but that was just a translation from ancient manuscripts, but I know what you mean.

MarkB_MI · Oct 21, 2014

I used to help my dad survey terraces, often over half a mile or more. He had a very good Leitz autolevel, and over those distances it's quite difficult to accurately read elevation even with a high quality instrument. Curvature of the earth? Forget about it.

IH2444 · Oct 21, 2014

There is more land on property surveys than available geographically. Property is surveyed in surface area. If there are hills and such then the total area sold as plots in a hilly area exceed the geographical area.

Frankmn · Oct 21, 2014

I think I remember from a history of architecture course that the Parthenon is constructed to compensate for the curvature of the earth.

Dell (WA) · Oct 22, 2014

shoot.....I knew that (frown).......Dell

Bret4207 · Oct 22, 2014

(quoted from post at 18:31:22 10/21/14) Actually, it was written about 400 years ago.

The earliest copies of Isaiah date from at least 100BC.

Knowledge is often lost and then "rediscovered". There is an ancient map from before the time of Christ that shows the land mass of Antarctica. That means mot only did people know and then forget an entire continent was there but that it wasn't ice covered when the map was made. There are still new species of plant and aninal being discovered today and quite a few "extinct" species that seem to turn up on regular basis.

Mans arrogance and hubris keep us repeating the same mistakes over and over.

showcrop · Oct 22, 2014

(quoted from post at 14:31:22 10/21/14) Actually, it was written about 400 years ago.

Semantics. If you want to call translating writing.

Leroy · Oct 22, 2014

And where would that higest point be. What part of the state. Here in Ohio the highest point is located just a bit southeast of Bellefontaine and that is in what could be called west central part of the state and in an area of farm ground, notin the montains like would be thought. I live about 40 mile east of Indiana.

qwertyell · Oct 23, 2014

Don't even bother! The "level" on your transit takes care of that for you. In actual happenings, if your concrete floor is level on one side and you move 20 feet to the other side and level it there then the two surfaces will not be parallel. The level will be tangent to the earth on the one side and tangent to the earth on the other side.... both sides perpendicular to lines that are not parallel to each other as they converge at the center of the earth. Think of it this way. Check your level where you're located and then in your mind go 1/4 the way around the earth and check it again. It will be 90 degrees from the plane you held it at on your first check. Go half way around the earth and the level will be parallel but will be rotated 180 degrees from it's first check. BUT, still level. All I can say is, "Thank God for gravity. It seems to work very well!"

Way OT: Elevation survey with Transit Rod

Member

Well-known Member

Member

Well-known Member

Member

Well-known Member

Well-known Member

Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Member

Similar threads