On Wed, Sep 30, 2009 at 10:02 PM, Dan O'Hara <detect...@yahoo.com.au> wrote: > Here is some info on the ACT grid > > "The ACT grid is a Transverse Mercator map projection that uses the > longitude of Mt Stromlo Trig Station as its central meridian. It is based > on the Australian Geodetic Datum 66 (AGD66), which is modified to take > advantage of the ACT’s limited east-west dimension and account for scale > differences caused by the ACT’s height above sea level. The resulting ACT > grid effectively can be treated as a plane (rather than geodetic) system of > coordinates using the formulae of plane trigonometry, without the need to > apply scale factors, grid convergence, arc-to-chord, or sea level > corrections. As a result, for all but the most accurate work in the ACT, > terrestrial, grid and plane measurements can be taken as being identical." > > http://www.actpla.act.gov.au/tools_resources/maps_land_survey/surveying_data/surveyors_information/coordinate_system > > I think the reason you didn't get a match is because the grid reference is > in yards not metres. Aha! Thank you! Using the downloadable tool they provide, I get the correct results and they match what I get when I run proj4 (via the definition at http://spatialreference.org/ref/sr-org/6628/ ): >>cs2cs +proj=tmerc +lat_0=0 +lon_0=149.00929483 +k=1.000086 +x_0=200000 >>+y_0=4510193.494 +ellps=aust_SA +units=m +no_defs +towgs84 +to +proj=latlong >>+datum=WGS84
211550.06 600190.55 149d8'10.668"E 35d18'57.41"S 22.802 = -35.31595, 149.1363 and my guess was -35.31415,149.1374 I did stare at it a while, hoping that adding the position of Mount Stromlo or something would give me the result in Excel. It does say "units=m" so I don't think the yards come into it (still doesn't explain the huge difference between ACT and AMG). But I suppose if someone wants to import this data, they could use PostGIS. _______________________________________________ Talk-au mailing list Talk-au@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk-au