On Wed, Jul 20, 2011 at 7:50 PM, Elizabeth Dodd <ed...@billiau.net> wrote: > Firstly, the mark shown in the nearmap imagery posted is a photo > control point, for aerial photography. They are not a great deal of > use because they are placed by private companies and are typically > only in place for the few weeks that the survey is taking place. Areas > such as mine sites may have more permanent ones, but they are still > privately owned. There are no publically accessible location data for > such points.
> As for the survey marks in general, I think that adding them to > the map is a good idea. However, it is important to remember that > surveying is a state controlled industry. Each state would have it's > own rules for the placement, naming and numbering of marks. I worked > across 2 states in the survey industry and the marks can be > surprisingly different. Numbering can be managed via the ref tag, postfixed with something like :nswssm to indicate that this reference id is for SCIMS State Survey Mark number. e.g. ref:nswssm=35225 > SCIMS lists 7 names for types of survey points. Of them, I > think that only the Mapping Control Point, Cadastral Reference Mark, > and Trigonometric Station are worth including. I saw those 7 SCIMS names from http://www.lpma.nsw.gov.au/survey_and_maps/scims_online/glossary They seem universal and easily applicable to other states and other countries. So for now I'm using this same terminology for my tagging. > Any marks on the ground for positioning aerial photography (or > other remote sensing) would be a Mapping Control Point. They will > probably not be permanent. > > Any small but permanent mark in the ground would be a Cadastral > Reference Mark. The Cadastre is the register of land boundaries and > ownership, and it is defined in Australia by distances and directions > from several Cadastral Reference Marks. State Survey Marks, Permanent > Marks, and Miscellanous Survey Marks are all types of Cadastral > Reference Marks. Interesting. Two features I've encountered which would fall under this category, but I thing should be tagged differently are white pegs, and small metal disks with a nail or something in the centre which have "STATE SURVEY MARK" engraved... How would these two fall into SCIMS? They may both be CR's, but I think they need different tags as they are different. I would have thought the peg would be a CR and the nail an SS since the nail says "STATE SURVEY MARK"... > Trigonometric Stations are generally older then Cadastral > Reference Marks, and are known more accurately. These are generally the > stations on top of hills with the black 3 or 4 legged stand, 4 metres > tall with a top section made of 2 perpindicular circles. Back before > satellite positioning, even back before electronic distance > measurement, those stations were put in place and located simply by > measuring the bearings to them, from any other station that could see > them. Then the whole network across a state was adjusted to minimise > the errors in the angles. Yep. > I would not worry at all about the Geodetic Bench Mark type. > There are few of those in Australia, and they refer to devices like > tide gagues or permanently operating GPS receivers that are used for > country or planet wide position determination. > > I hope that I have made things clearer. If not, I am available > to answer further questions. > _______________________________________________ Tagging mailing list Tagging@openstreetmap.org http://lists.openstreetmap.org/listinfo/tagging
