Bruce, Take a look at some military maps. A common feature is in the margin that shows the distribution of spatial POSITIONAL accuracy based on various sources. It gives the Field Commander some idea regarding the reliablity of mapped features and positions for artillery fire control. The compilation process in a military mapping agency (Australian as well as U.K. & U.S.) includes the evaluation phase early in the collection process. Most topographic mapping throughout the world (except for our mapping of the communist territories) was NOT done with "Keyhole" satellites. It was done through aerial photogrammetric processes that ran the gamut from slotted-template mosaics (Directorate of Over Seas Territories did a lot of that) to full-blown analytical aerotriangulation controlled metric photography. All of this was based on classical triangulation arcs that were evaluated as to their inherent accuracies, including the plotting of trig stations with respect to the graticules on printed maps. The accuracies of these triangulations were computed from the "Trig Lists," or lists of triangulation station coordinates and adjusted directions to connecting stations in the chains of quadrilaterals. Junction points with connecting arcs were/are intensely examined as indicators of propagated errors, and serve(d) as excellent bases of comparisons of accuracies. There are still significant areas of the world that have "currently-published" topographic maps that to some degree or another still rely on 19th-century planetable and alidade surveys! The evaluation of this material is a critical part of Military Intelligence that is handled by senior cartometric cartographers. "Map Evaluation Branch" is a familiar term used for such activities, it is always classified secret, and the methods used are published by D. H. Mailing. The methods and techniques for assessing the positional accuracy of printed maps is not classified. The methods and techniques for gathering the material that is used for such assessments is damned classified! Nowadays, it seems that such a task of cartometry is impossible, but only on the surface. The methods that are "easy" to use on paper are currently quite difficult to use in digital form because of the inconvenience of the CRT and tabular data. If you study the philosopy of the cartometric principles and the foundation of the accuracy evaluation of printed paper maps, you can glean some insight as how to classify metadata accuracy with respect to positions. I do not know of commercial software that is set-up to do such a thing, but essentially you have to first be quite cognizant of the history of map compilation and production methods. When presented with two data sets, you need to do a comparison of the fit of detail. An easy way to do this is to get hard-copy plots of both data sets at the same projection and scale. Visual comparison over a light table is quite straightforward. However, when discrepancies are found, which data set do you favor? You need to be cognizant of the history of the geodetic and topographic surveying of the area. Do you read my columns in "Photogrammetric Engineering and Remote Sensing?" In the absence of a second data set to use for comparing, then the only recourse is to do a field check. Go out in the field and run profiles to check topographic fidelity. Do a number of resections and compare instrument location on the ground to interpreted instrument location on the map. You need to obtain the Trig Lists for the area and compare the coordinates of the triangulation points on the map (or digital data) to the Trig Lists. (This will in all likelyhood involve some raster to vector work with images of triangles with respect to images of the surrounding Grid/graticule lines.) On occasion, you have to do comparisons of like data in a variety of Datums and Coordinate Systems and Grids. In Cartography, there is no substitute for years of education, independant study and experience. I do not see it becoming a "mouse click away" in the forseeable future. Want an example of "current events" where cartometry was an insufficient qualifier for data reliablity? Remember the three Chinese reporters killed in the recent bombing of Belgrade? Lousy accuracy? Nope. They hit the exact building they wanted to hit ... accuracy in itself does not make a reliable map (or target). The human component in cartography (current buzz word is "GIS") will not be replaced anytime soon. When you want to evaluate a data set, not only do you have to rate the cartometric accuracy, you also have to rate the attribute accuracy otherwise known as "revision date." In digital form, that is quite elusive. In fact, it lends a "Polyanna" air to the concept of "metadata." Clifford J. Mugnier ([EMAIL PROTECTED]) The Topographic Engineering Laboratory Department of Civil and Environmental Engineering UNIVERSITY OF NEW ORLEANS New Orleans, Louisiana 70148 Voice and Facsimilie: (504) 280-7095 On Friday, 18 June, 1999 9:24 PM, Bruce Bannerman [SMTP:[EMAIL PROTECTED]] wrote: > Cliff, > > Thanks for your help once again. I'll look into your > suggestions. > > I've spent the last three months looking in depth at the > problems of spatial data accuracy, in particular it's > inherent error and uncertainty. > > I'm trying to get an understanding of how organisations > estimate the residual error in data. To date most > standards that I've reviewed use the concept of a 'well- > defined' point to measure the residual error using various > methodologies. > > You also guessed right...I'm unable to read German or > Russian. > > Thanks again. > > Regards, > > Bruce > > Bruce Bannerman > GeoInnovations Pty Ltd > Darwin > Australia > ========== > [EMAIL PROTECTED] > http://www.geoinnovations.com.au > ========== > > > -----Original Message----- > From: Cliff Mugnier - University of New Orleans > [SMTP:[EMAIL PROTECTED]] > Sent: Friday, June 18, 1999 11:21 PM > To: Bruce Bannerman; [EMAIL PROTECTED] > Subject: Re: (GIS-L) Spatial Data Accuracy Standards? > > Bruce, > > The "Bible" of Cartometry is D.H.Mailing's "Measurements > from Maps." I think it > is still in print. ISBN0-08-030290-4 Pergamon Press, > 1989. (If you don't have > a copy, I highly recommend getting a copy, even if you > have to get it from a > used bookseller.) > --------------------- > There's also ISO/TC211 N459 Geographic > information/Geomatics > http://www.statkart.no/isotc211/ (This is more on the > "definition" of metadata > standards in the realm of coordinate systems and the > corresponding statements of > the accuracy of the data contained therein rather than how > to ASSESS the > accuracy.) > --------------------- > "The Positional Accuracy of Maps" by Andrew M. Glusic, > Army Map Service > Technical Report No. 35, March, 1961, 63pp. > --------------------- > Everything else I know about is in either German or > Russian, I guess you're not > interested in those. > > > Cliff > > -- > Clifford J. Mugnier ([EMAIL PROTECTED]) > The Topographic Engineering Laboratory > Department of Civil and Environmental Engineering > UNIVERSITY OF NEW ORLEANS > New Orleans, Louisiana 70148 > > Voice and Facsimile: (504) 280-7095 > ------------------------------------------------------ > Bruce Bannerman wrote: > > > > Hello everyone, > > > > Can someone please point me in the direction of > > recommended Spatial Data Accuracy Standards? > > > > I'm currently reviewing methods used to estimate the > > residual error in spatial data. I am aware of: > > > > 1. The US National Map Accuracy Standard, > > 2. The ASPRS Accuracy Standards for Large-Scale > > Maps, and > > 3. The US FGDC National Standard for Spatial Data > > Accuracy. > > > > What other applicable standards in there? > > > > Please provide a relevent URL if possible. > > > > Regards, > > > > Bruce Bannerman > > GeoInnovations Pty Ltd > > Darwin > > Australia > > ========== > > [EMAIL PROTECTED] > > http://www.geoinnovations.com.au > > ========== ---------------------------------------------------------------------- To unsubscribe from this list, send e-mail to [EMAIL PROTECTED] and put "unsubscribe MAPINFO-L" in the message body, or contact [EMAIL PROTECTED]
