+Black Dog Trackers Posted November 12, 2008 Share Posted November 12, 2008 I'm attempting to further my education here, so I thought I'd expose my level of ignorance and ask a few questions.... I thought I knew a lot about surveying and the uses of survey marks, but after reflecting on it, I find that I really don't know much about them. Hopefully some people who know more than I can explain some or all of these things. Horizontal control and Vertical control marks are aspects of geodetic surveying but Cadastral is not. Geodetic surveying determines the position of points with respect to the Earth's geoid, longitude and latitude. Cadastral surveying only relates to local and distant borders, I think. Techniques I think I understand very basically how horizontal control is done - either by measuring distances, azimuths, and vertical angles, or by using GPS, and then using an adjustment program to resolve a net of such control points.. Vertical control also uses the measurement of distances and vertical angles, or perhaps just distances and something else, I don't know. Whether or not angular measurements are used at all is unknown to me. In any case, it is also adjsuted by a computer program to resove a vertical control net. Cadastral surveying is even more of a mystery to me than vertical control. I can find no explanation on the internet as to how it is done. Certainly distances and horizontal angles are used, but I don't know what's done about the vertical component. Does a property on a mountainside have more surface area compared to the same 'size' property on flat land, or is it the same surface area? I don't know if cadastral surveying can make use of GPS technology. Another puzzle to me is why the central and western U.S. has a lot of cadastral marks while the eastern third doesn't seem to have many cadastral marks. I realize that the borders of the western 2/3 of the country tends to have been laid out on grids, but both the whole country has borders. It would seem that the more complex eastern third would be more in need of cadastral marks. Uses It's pretty obvious that geodetic control is involved with mapmaking, and cadastral surveying is involved when property (private or municipal) borders and boundaries need to be established or re-established. Beyond that generality, I'm not sure of exact uses, for instance, if a new building is to be built, is geodetic surveying or cadastral surveying required, or both? Railroads and bridges tend to have vertical control marks. Is it that no one cares if a bridge is moved downstream a bit by a storm or car accident, just so it isn't any lower or higher? Is it a grade issue, where car roads and railroads need to be messured in terms of vertical distance for some reason? Are the marks established to help build these roads, or are they established after construction, as some aspect of maintenance? I can see that if a building is to be built, it must be located well within its proper property boundaries, and cadastral surveying does that, but what then are geodetic horizontal control points for besides making paper (or computer) maps? Do cadastral systems ultimately depend on geodetic control? Even more obscure Even more obscure are magnetic stations and gravity stations. Are these remnants of scientific research projects? There are gravity anomalies that warp the geoid but what do these stations do? There's a mountain road vaguely near here that has at least 20 gravity stations on it. There's no mining there anymore, if there ever was much, so what was the curiousity that was or will be satisfied by these gravity stations? What does a gravity station do that a vertical control bench mark does not do? Quote Link to comment
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