[GRASS-user] Reprojection help

Richard Chirgwin rchirgwin at ozemail.com.au
Sat Aug 11 03:59:27 EDT 2007


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!

> 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?

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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>> grassuser at grass.itc.it
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