Team Fawlty Posted May 6, 2006 Share Posted May 6, 2006 What does this mean - HEIGHT OF LIGHT ABOVE STATION MARK n METER(S)? Thanks Brendan Quote Link to comment
2oldfarts (the rockhounders) Posted May 6, 2006 Share Posted May 6, 2006 What does this mean - HEIGHT OF LIGHT ABOVE STATION MARK n METER(S)? Thanks Brendan Team Fawlty, Welcome to the world of benchmark hunting. Here is a link to a picture that is from the NGS photo gallery. A person in a tower measuering Height of Light. This is a quote from survey tech - June 8, 2002.. Hello everyone, Im here to promote, and to thank you for, your interest in Land Surveying .Lights were frequently used as targets for surveying observations at night. The work was done at night to avoid the effects of heat wave distortion over long distances which made obsevations taken during the day less accurate. In many cases the lights were mounted on towers, up to about 10 meters high in order to be visible above trees, buildings and other obstacles. In fact the surveyor, with his instrument, was often set up in a tower as well, to get above the obstacles. This was neccessary only in relatively flat areas. In hilly or mountainous areas, the highest possible locations for the markers were selected in order to avoid the need for towers. In many remote places, where little or no development of the land has occured, the remains of the old wooden towers are still there to be seen, decaying into ruins. Later, collapsible modular metal towers came into use, which were assembled and disassembled on site, then transported and reused. For more information on Land Surveying, please feel free to visit rpls.com, and ask any questions you may have. That came from this thread. And this comes from Kewaneh & Shark, March 28, 2004. A triangulation station is a mark that is used in a triangulation survey, and, as its name imples, triangulation utilizes geometric figures composed of triangles. These triangles are used to help define the shape of the earth. The marks which are used are often times quite distant from each other, sometimes many miles apart. Because the great distances, it was sometimes difficult to see between the stations during the day, due to the heat of the day and other atmospheric conditions. Many of the surveys were conducted at night when it was possible to see farther. In order to help pinpoint a particular station a light was suspended directly over the triangulation station, from a few feet up, to a over a hundred feet in some cases with the use of a tower. It was necessary to know the 'height of the light' to accurately determine the correct vertical position as well as the horizontal position of the station. Some other threads that might help explain the 'height of light' are... What is HEIGHT OF LIGHT??? What is HEIGHT OF LIGHT? "Height of light" height of light? Good luck in your hunts! - Kewaneh I hope all of this has answered your question. Good hunting! Shirley~ Quote Link to comment
Z15 Posted May 6, 2006 Share Posted May 6, 2006 (edited) Height of light above station - The distance from the survey mark to the center of the light (which is the object they used to sight upon). Lights are used for long distances. Other targets cannot be seen over great distance. The height is needed for the trig computations. Th farther above sea level you go, the greater the distance between points and thus you have to know the various elevations differences between the surveyed points to determine accurate position. Edited May 6, 2006 by Z15 Quote Link to comment
2oldfarts (the rockhounders) Posted May 6, 2006 Share Posted May 6, 2006 Height of light above station - The distance from the survey mark to the center of the light (which is the object they used to sight upon). Lights are used for long distances. Other targets cannot be seen over great distance. The height is needed for the trig computations. Th farther above sea level you go, the greater the distance between points and thus you have to know the various elevations differences between the surveyed points to determine accurate position. Z15, Do you have any personal old pictures of these? Did you ever have to climb one and occupy it for any length of time? Inquiring minds of us hobbyists... Shirley~ Quote Link to comment
68-eldo Posted May 7, 2006 Share Posted May 7, 2006 (edited) Height of light above station - The distance from the survey mark to the center of the light (which is the object they used to sight upon). Lights are used for long distances. Other targets cannot be seen over great distance. The height is needed for the trig computations. Th farther above sea level you go, the greater the distance between points and thus you have to know the various elevations differences between the surveyed points to determine accurate position. I found that sometimes (at least in this area) the term is used without actual lights. This type of station is common here. In the 1969 recovery of Ewa Church Reset the term "height of the light above the station" is used. Maybe it's just a local thing. If the lights are temporary why would the height be listed in the data sheet? Wouldn't it depend on the preferences of the survey party and what they had available at the time? Edited May 7, 2006 by 68-eldo Quote Link to comment
Z15 Posted May 7, 2006 Share Posted May 7, 2006 (edited) Do you have any personal old pictures of these? Did you ever have to climb one and occupy it for any length of time? Inquiring minds of us hobbyists... No. I worked for a state DOT. Back around circa 1977 our dept assisted NGS in a tower survey of SE Michigan. I was offered a chance to go work with NGS as a lightkeeper but I cannot climb heights. Some others I worked with did and said it was boring. All by yourself sitting on a tower till dawn. A loner job. These are all the photos I managed to save in 30 yrs (was not much of camera buff). Misc Photos Edited May 7, 2006 by Z15 Quote Link to comment
Bill93 Posted May 7, 2006 Share Posted May 7, 2006 Mike's Triantulation5 and related ones in that set illustrate the angles they measured in order to calcualte horizontal position. Somewhere there are a couple known base line distances, and the rest is done from the angles. Quote Link to comment
2oldfarts (the rockhounders) Posted May 7, 2006 Share Posted May 7, 2006 Do you have any personal old pictures of these? Did you ever have to climb one and occupy it for any length of time? Inquiring minds of us hobbyists... No. I worked for a state DOT. Back around circa 1977 our dept assisted NGS in a tower survey of SE Michigan. I was offered a chance to go work with NGS as a lightkeeper but I cannot climb heights. Some others I worked with did and said it was boring. All by yourself sitting on a tower till dawn. A loner job. These are all the photos I managed to save in 30 yrs (was not much of camera buff). Misc Photos Thank you Mike. We enjoyed looking at them. Shirley~ Quote Link to comment
+bicknell Posted May 7, 2006 Share Posted May 7, 2006 I always assumed they told you the height so if you were going to bring out a tower for the next survey you knew how tall of one to bring! That's all. Quote Link to comment
DaveD Posted May 7, 2006 Share Posted May 7, 2006 Bicknell is correct in the assumption that the heights of lights in the descriptions and recoveries would provide information to network survey planners about what kinds of resources would be needed when the station is used in future triangulation surveys. Since NGS abandoned this technique in favor of GPS in 1984, this is now just a part of the survey history. The heights of lights also indicated to local surveyors something about the conditions around the mark before they would go to the field. Since C&GS/NGS were the only ones with towers (with a couple of notable but rare exceptions) this information would let the local surveyor know what could be seen from ground level. The establishment of Azimuth Marks for most triangulation stations was necessary because towers or tall stands (such as the 9.5 ft stand at EWA CHURCH RESET in 1969) where the norm and without a mark for orientation (azimuth) the station was much less useful to surveyors. Tower building was an integral part of the education of geodetic surveyors by C&GS/NGS. My first day on a triangulation party, even though I had 3 years experience as a geodetic surveyor in the Army, the Chief of Party handed me a shovel to dig tower anchor holes and he let me known in no uncertain terms that my career in NGS was to begin on the building party. His words of wisdom were "You'll like working for the Coast Survey because we only work half days -- anything after 12 hours is all yours." He was right!! Quote Link to comment
Team Fawlty Posted May 8, 2006 Author Share Posted May 8, 2006 Now that is a wealth of information. Thanks to all. Brendan Quote Link to comment
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