[GRASS-user] Reprojection help
bain at toraval.fr
Sat Aug 11 07:47:18 EDT 2007
Le samedi 11 août 2007 à 17:59 +1000, Richard Chirgwin a écrit :
> Vincent BAIN wrote:
> > Hello Richard,
> > don't know if it can help, but for me it works, from conformal conic
> > Lambert to rgf93 (the official geographic coord system in France,
> > compliant with wgs84).
> > Could you send us the proj information from each of your locations, and
> > make sure they correspond to your project ?
> The XY location was defined using EPSG code 20356 (Australia from
> Geosciences). It shows UTM projection, zone 56, AGD84 datum, and
> ellipsoid data.
> The LCC location was "self-defined" during import - that is, I created a
> new location during import. The project info it created is below:
> g.region -p
> projection: 99 (Lambert Conformal Conic)
> zone: 0
> datum: towgs84=-134,-48,149,-0,-0,-0,0
> ellipsoid: a=6378160 es=0.006694541854587638
> north: 6784163.1212489
> south: 3123142.28999373
> west: 2961606.17926652
> east: 6874125.97609581
> nsres: 183051.04156276
> ewres: 195625.98984146
> rows: 20
> cols: 20
> cells: 400
> The problem is that I don't know what EPSG code the creator of the
> mapset I'm trying to import was using!
You mean : you have data in XY coordinate, but you don't know what coord
system it's linked to ? then it's a serious problem :-)
maybe you can try with a "standard" lambert in use in Australia
> > I advise you to define the coordinate systems from epsg codes, the best
> > way -- i think -- to avoid problems defining the right ellipsoïd, datum,
> > and so on...
> > And be cautious: the coordinates read from the display are decimal...
> <whacks forehead> I suspect you're telling me I should be using
> degree-minute-second format in my transformation?
I just meant sometimes we careless try to check the transformation by
comparing decimal values of coordinates to deg,min,sec values... (it's
the kind of mistake I do every day !)
> Thanks, I will go back and look at how I can get the projections lined
> up ... I might try defining a standard Australian LCC and see if the
> import works; then from a standard location to a standard location might
> well be easier.
> > Bon courage,
> > Vincent
> > Le samedi 11 août 2007 à 09:32 +1000, Richard Chirgwin a écrit :
> >> It's me again ... I suspect I must be stupider than most Grass users
> >> because I seem to be hitting the list with questions so often!
> >> I have my own maps which are in lat-long format, using Australian
> >> boundaries.
> >> I need to analyse some points relative to some centroids supplied in
> >> MapInfo format. They import fine, but they're in Lambert Conformal
> >> Conical projection.
> >> Without being long-winded, my attempts to reproject the LCC location
> >> into a lat-long UTM using WGS84 keep failing - the utilities work but
> >> the result isn't right.
> >> Is there something about LCC projections that make them hard to reproject?
> >> Richard
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