studiot

Here is an worked example of pure simplicity and accuracy for the Institute of Structural Engineers levelling in a similar situation. Please read the sections in the order 1,2,3 I have labelled on the left hand margin as I have cobbled together from several pages.

"PS I am only posting in Philosophy because I fear my question may be too insubstantial for the Relativity Forum where I intended to put it" Good question and good place to put it since philosophy is the place for garbled thought processes. But it is not a stupid question so +1 In particular "Are Motion and Time joined at the hip?" No they are not. It is possible to separate them. But I don't think you were expecting this sort of answer. The wave equation is officially an equation of motion - wave motion. There are two forms of solution to the wave equation, called travelling waves and stationary waves. For travelling waves distance and time are indeed joined at the hip. But for stationary waves they have been separated and solutions which contains only distance are available. ​That is why we say the stationary or standing wave is time independent, (Note this is a less garbled phrase), even though if we look at standing waves on say a stretched string the string is actually in motion.

Sandor, I am sorry you have decided to reject my suggestions since they are based on sound principles that carry enormous weight in all walks of experimental science. The most powerful and persuasive experiments are those that have corroboration by independent measurement ie measurement by other means. This is what I was offering you. Earlier in the thread you stated that you have a mathematics degree, and yet you asked me about interpolation v extrapolation. Interpolation is all about working from the whole to the part. Establishing control or reference points outside and perhaps throughout your working region. This is true in large scale physical surveys and abstract finite element analyses. And this is what you are lacking here. The proper establishment of a few control points on a traverse would set any measurements on a proper footing and reduce the fancy corrections and corrections on corrections Mordred proposes to an academic exercise (sorry Mordred). This is basically a simple exercise and with proper methodology it could be a tight and accurate survey. A final suggestion. I am not sure you appreciate the difference between distances on maps, the geoid, the spheroid, the gps system and in actual measurements. They are all different and it is important to avoid offering figures from one system that were made in another.

Isn't one poorly managed laser moredred than enough? I noted the safety implications earlier. Any laser with enough punch to produce a visible light by day at several km range is potentially dangerous. Yet none of the crew were wearing eye protection and several were seen looking into the beam in the video. Perhaps Mr Maker's comments about beam spread were an underestimate - this would lead to a safer beam. Further the measurement of vertical angles by ordinary means as would allow direct calculation avoiding the built in corrections for curvature available in more sophisticated equipment. Dark star Thank you for your comments, I note your post#108 and others I see nothing in the composite fig2 posted in post#1 to substantiate or refute the statement that the lidar survey shs the water surface to closely followed the local curve of the geoid, although I would expect this to be the case. There is just not enough information there to make such a judgement. Of course there would still be a geoid curve if the Earth was flat and the water would still more or less follow it, as would the underlying lakebed. Sandor Thank you for your recent replies, it would be good if you would also reply to my most recent posts as they contain genuine well intentioned advice to help your group proceed.

Michel, please be advised that intervisibility is more complicated than this. In general it depends where the obstruction is along the line. In the second case you show, you would need to remove the entire bulge, not just part of it, to allow intervisibility. So this would be appropriate if the model of the Earth was a faceted solid,. But we seem to be debating a flat Earth which is different.

Have I accidentally stumbled on the jokes thread?

Sandor, in response to your post#92, my thoughts now are. 1) I am pleased if you wish to turn this into a proper scientific experiment. 2) Go to the university and find a proper surveyor. Buy her a cup of coffee (take her out to dinner?) and run my post#88 and the rest of these thoughts past her. 3) Send the laser back to the fairground and save the money. 4) Depending upon your budget hire a shore base tacheometer (Wild RDS etc) or a Total station. 5) Fix an outrigger pontoon on the boat and paint a large target at water level. 6) Sight on this target with your new equipment. It will give you sufficiently accurate horizontal distance and heighting over the ranges you are actually using. 7) Track the boat + pontoon on a series of traverses across the bay during daylight hours. This leaves the night for dancing etc. 8) Good luck in your mission, should you choose to accept it. 9) This post will self destruct in 9,000 years.

Wouldn't work directly. The experiment relies on using the laser line as a reference to measure from, and that reference line is supposedly set horizontal. A laser in a boat would not be horizontal without some very sophisticated mechanical mountings. I am suggesting something quite different.

Another good reference is a refutation by John Polkinghorne 'On Space and Time' page 279 The book oS&T is a recent collection of papers from several famous physicists and mathematicians, published by Cambridge University Press.

Thank you sensei for some good thoughts, particularly as it allowed me to locate and watch the video this morning. (I did not see it before the original link was removed which is why I kept asking for method statements) +1 My thoughts on the 'experiment' are 1) Safety - No one was wearing eye protectors, yet those in the boat often looked into the laser beam. 2) It was never clear what the vertical angle of the laser was or if there was a vertical angular readout. It was however stated that one some occasions the laser was 'tilted down' to compensate for the curvature of the Earth. Perhaps this is why no extended board was need. 3) How the distances to stations C1, C2 C3 etc were obtained was not clear. 4) Some attempt was made to find the cente of the beam by measuring the upper and lower limits of the light spot and splitting the difference. This is correct procedure and corresponds to standing theodolite instructions (which are better) to read both the upper and lower stadia lines to avoid misreading a staff. 5) All this was really showmanship and quite unnecessary. Better results could have been obtained by standard tacheometry or just reading vertical angles, sighted onto the same point set low on the boat and using a purely optical theodolite or a digital station. Why try to measure up and down a scale jigging about on a small boat when you can stand firmly planted on shore and measure the scale there as an angle sighted to a particular spot on the boat as it moves around the lake?

Interesting observation. Welcome to Scienceforums. Please fill in a few more details of the experiment. Was the camera used on the beam at 100oC Why was the beam heated? Was this done after the (surface) rust was removed? Was the experiment continued long enough for the beam temperature to equalise? Corrosion involves the establishment of chemically different zones on the surface and within the body of the material. As the corrosion proceeds the material in these zones (called anodic and cathodic zones) changes chemical composition so the beam material is is no longer homogeneous. I suspect that this has something to do with the phenomenon, but more details are needed please.

Try this experiment, next time you are washing up. Submerge a stack of plates in the washing up bowl. Swirl the washing up mop above the stack creating a whirlpool. Watch the top plate rise in the whirl up off the stack. I suggest that the plates stick together due to residual material and air trapped between the plates. The air will be at atmospheric pressure when dunked. The water will be at slightly higher pressure. This will tend to hold them together like the magdeburg hemispheres. www.google.co.uk/search?q=magdeburg+hemispheres&rlz=1C1AVNG_enGB673GB673&oq=magdeburg+hemispheres&aqs=chrome..69i57.9387j0j8&sourceid=chrome&ie=UTF-8

Thank you again, Boxer for the partial explanation. But still why present the data as a histogram? If we regard this as a statistical sampling of the surface water then it seems to point to the Wiki number of 105 being the mean of the histogram. But this information is useless without knowing what part of the water surface was sampled. All the flight paths were along the edge. Like the rest of the information provided it requires a proper method statement and declaration of variables to accompany it to make any true sense of it. Further none of this alters the possibility of local flatness of the geoid and ground surface (ie the lake bed) supporting a flat water surface since the geoid 'corrections' are not shown.

Michel, Boxer thank you both. So which height is shown in the histogram and why is it shown as a histogram? It is listed at around the 150m figure. Here is an extract from Wiki Which is 45 m different. So which height is which?

Yes we all would like some hard information instead of a half hour video and a proper method statement, along the lines of the two in my post#40. As to how the butler did it, Japp, I don't know but here is another story from memory lane. My firm was commissioned to design and oversee the construction of a border outpost town in Saudi Arabia. I was twice sent there to sort out problems that had arisen, the first time was to help the contractor figure out why his setting out was going haywire. This was the first time in my life I found the need to apply temperature corrections to a steel tape - but that is another story. The second visit they had many buildings constructed, but it was discovered all the floor slaps had been cast with no level control. That is they were all set to random levels. In order to establish these slab levels so we could redesign the roads, I took a doorstep level on each building and caused consternation back home when the level book was returned. As this was in the Saudi/Quatar desert the buildings were flat roofed. I set up a level on top of a central roof and fixed leg, several metres long to a standard (3m I expect) levelling staff. This I sent round with a couple of assistants to stand on each doorstep in turn. It was necessary to perform the staff waving exercise I noted with the boat's mast earlier in this thread. When they saw my results, head office couldn't understand how I had 8m staff readings recorded in my book. If you are making a valiant effort to warn us of something but struggling with English, thank you very much. But I find your statements more bizarre than those of the OP. I have already asked you to elaborate.

Are you suggesting that geological processes such as mountain upthrust, volcanoes, rifting, follow geopotential lines? Perhaps you could explain? Do you also think they follow Ley lines?

Fracture lines AKA displacement lines in both materials science and physical geology tend to be straight rather than curved. Indeed they often cut across curved structures such as folds as can be seen at many classical unconfomities in geological sites and textbooks. This characteristic can be deduced from energy considerations. Who said Nature avoids straight lines?

In essence, yes. But for 3 there are many such rift lakes, including one nearby that is 1m deep (Neuseidler See). Of course the Red Sea is much deeper. Note I used the word flat, not level, although rifts are no respectors of level lines either.

It would appear that the OP is indeed another attempt to push the misguided flat earth dogma. However instead of ridicule or minor arguments against his results we should all consider this. Sandor's results, if the survey was properly conducted, will be correct. The water surface departs from following the Earth's curvature; it is essentially flat. Note my question in post#6 that has gone unanswered Lake Balaton is an important lake because of its size and topography. Only 12 metres deep at max and much less on average as my early question shows there is a basic issue with surveying the water/air surface. [aside]Although I have not been there since 1956 and at that time I was too young to be interested in geomorphological history, my daughter had a wonderful holiday there earlier this year. I can definitely recommend it, it is one of Europe's Geopark sites.[/aside] As such it has attracted much august study about its formation which reveals the clue to the conundrum. Lake Balaton is a rift lake. That is it lies in the bottom of a rift valley. Rift valleys, such as the African and Red Sea rifts, are noted for their flat bottoms, which can run for great distances. Rifts are no great respectors of the Earth's curvature. So the underlying topography is, well, flat. And a very shallow lake has formed with sediment deposits on the rift valley floor giving a slight slope to the bottom. But since the average depth is only about 3 m How can the water surface not be as flat as the ground on which it is resting? This is not support for the flat earth view, just modern science sorting the fact from the fiction and properly acknowledging real facts. Here is a sketch geo history of the rift.

Good point, +1 Variation of spot size is an important point when finding the centre of a laser beam. Are you aware that a collimation error of 0.001 degrees corresponds to 1.3 metres at 77km range? By the way, .001 degrees is nearly 4 seconds of arc and pretty poor accuracy for this sort of work. Standard geodetic work at this range would be at least two orders of magnitude finer and really accurate work better still.

Refraction may or may not be significant, depending upon circumstance. Here is a circumstance when it is definitely significant. This really happened in the early days of pipeline alignment lasers during the construction of the Alaska pipeline. As Robert Service says, it gets a mite chilly up there. However the air in the main trench was warmer and stable. Except where a cross trench entered. This deposited cold air as a block like the perspex one in the pic across the main trench and cause a similar offset in the laser alignment line. This however was not what I was referring to here Some time after the pipeline event, I was working on the construction of a new factory to make car engines. This was basically a large shed with a roof supported on a grid of stanchions. A laser had been used by the contractor to establish benchmarks on these stanchions. The contractor had not considered earth curvature or atmospheric refraction worth allowing for. The factor housed a number of flowline machines several hundred metres long that required to be level to a couple of millimetres. Being the suspicious so and so that I am I did not trust these all to convenient benchmarks so I obtained a bag of coach bolts and set one into each base as they were cast, at about 15m intervals. After they were set I connected them as my own benchmarks to the others. In this way I carried a system of benchmarks across the building floor and used them to construct the machine bases I had responsibility for. By the far side of the building, there was a discrepancy between my bolts and the laser of 12mm. I had calculated the curvature as 15mm across the building, reduced by refraction to 13mm. All the bases constructed against the laser had to be recast. It was a system similar to this I was referring to for the OP hydrographic survey. Note also it is very bad practice to refer to the corrections as X per mile or per km because the corrections are proportional to the square of the distance, not the distance itself. This is why such surveying is best conducted in a series of short legs as I have already indicated.

The maximum stated observational distance was 720 metres Further the article is entitled 'over 6 km', which I think was broken down into small observational legs, with full calculational closure. That is certainly the way I would have tackled it, and one of the details I await confirmation (or otherwise) of.

I have quite a few comments yet to make, but I'm stuck with this windows 10 piece of c___p and I don't propose to fight it tonight. I do reiterate that refraction is a red herring here, the effect is too small to argue about. Further correct observational methodology will eliminate it. So we need to know more information about this. I am concerned that the OP says he can only place 5 answers and is up to his quota for the next 10 hours (5 now) so I await his answers with interest when they come. Think also about this methodology on the boat mentioned. On land the principal source of levelling error is due to non perpendicularity of the staff. Some part of the apparatus appears to have been mounted on the mast or similar of a boat, which must pitch, yaw and roll. How was the non perpendicularity of the mast taken into account?

Sandor, you truly are a magician. You managed to quote my post#20 in your post#19 It really is wonderful that you can answer my questions, before I ask them. Nevertheless I thought that both my diagram in post#14 and subsequent repeats of the question were plain enough. What is the shape of a surface 3m below one you claim is dead flat, if it is not also dead flat?

Please separate quotes and answers as here when replying. It is much more difficult for all otherwise. As far as I know there is no limit on the number of (sensible within the rules) replies you may make on this site, certainly it is far in excess of 5. I am interested in you methodology because of your apparent claim that the water surface is flat over a distance of 77km, yet is only a couple of metres deep. Therefore the lake bed under the water must also exhibit this characteristic. We have both agree that the deviation from a spherical surface over this distance is of the order of several hundred metres. Since a 3m layer of water apparently exhibits this, the lake bed underneath it must also exhibit this. Hence the bulge. I have repeatedly asked you to clarify this point and you have repeatedly avoided it. Arguing about whether a minor correction of a few millimeters to several hundred metres is upwards or downwards is irrelevant.