[Qgis-user] CRS Transfer MGA94 <-> AMG94

[Brett Adams]

Hi Ramon,

Not sure what going on with problem 1. Thats weird.

I'm no expert on Problems 2 and 3 but I was derailed by the same issue.  
Problem is that QGIS can't distinguish between GDA94, AGD84 and AGD66. 
It doesn't contain the required projection definition files. These will 
all silently default to WGS84 (or WGS72 occasionally).  This also true 
if you import mapinfo files with these projections, QGIS doesn't 
recognise them and they default to WGS84 which means they are upto 150m 
out of position (AGD84 V's GDA94).

My understanding is that the problem lies with Proj4, the projection 
reference system used, but not developed by QGIS. We looked into getting 
the bug squashed a few months ago but it didn't work out, probably 
because QGIS has no control over Proj4

Have a look at 
http://blog.gmane.org/gmane.comp.gis.gdal.devel/month=20060301 for 
another discussion on using AGD66 / AGD84. It also contains the 
projection definitions. In theory you could create your own CRS entries 
for your area. My solution was to swap programmes.

I am yet to see a solution for the Windows format but I believe the 
Linux version works if you insert the correct gsb files.

I keep an eye out hoping this issue will get fixed as I really like QGIS 
as a package, I just can't use it.

-- 
Brett Adams
Spinifex Geophysics <http://www.spinifexgeophysics.com.au/>
0438 861 974
SKYPE:brettadams_spinifex




On 21/12/2010 5:50 PM, Micha Silver wrote:
> Ramon Andinach wrote:
>
>> Hello,
>>
>> I am wanting to take a set of points stored in csv format that are in 
>> the projected CRS GDA94/MGA94 zone 51 (MGAz51) and end up with a csv 
>> file with the same points in CRS AGD84/AMG zone 51 (AMGz51). Being 
>> able to do this is useful for reconstructing some historical datasets 
>> that I deal with.
>
> If all you need is the new AMG z51 coordinates, you might want to try 
> using cs2cs to do the conversion. You could script this to create a 
> new CSV file from the original with two new columns for the new coord 
> pair.
> Here's a one liner to get started (tested on linux):
> while read line; do echo $line | gawk -F , '{print $13"\t"$12}' | 
> cs2cs +init=epsg:28351 +to +init=epsg:20251;  done < MGAOnlyAC.csv
>
> Columns 12 and 13 are the N and E coords, but in "reverse" order. The 
> gawk output gets piped straigt into the cs2cs utility, which then 
> dumps (to the screen, at this point) the coordinates, transformed from 
> EPSG 28351 (MGA z51 ) to EPSG 20251 (AMG94 z51)
>
>> I was intending to use the following path, but have hit a few 
>> problems on the way. These are using qgis 1.6 on win7-64bit by osgeo, 
>> and was updated last thursday. At least Problem 1 has been duplicated 
>> using qgis 1.6 on ubuntu 10.4, the others I have yet to have an 
>> opportunity to test.
>>
>> 1. Import CSV using the Delimited Text Plugin (Problem 1).
>> 2. Save as a shape file in MGAz51.
>> 3. Load shape file
>> 4. Export to AMGz51 using either;
>>  a. Vector -> Data Management Tools -> Export to New Projection 
>> (Problem 2), or
>>  b. Save As and select a different CRS (Problem 3)
>> 5. Load new shape file.
>> 6. Extract coordinates using Vector -> Geometry Tools -> Export/Add 
>> Geometry Columns and then
>> 7. Save As a CSV.
>>
>> So my first question is, is this path reasonable? Is there a better way?
>>
>> Problem 1.
>> I experienced problems importing a text file. In the Delimited Text 
>> dialogue box the file appears to be correctly parsed, and I can 
>> select the correct X and Y fields (East_MGA94 and North_MGA94 
>> respectively). However on import data is scattered all over the 
>> place, and most fields do not have data in the X and Y columns. This 
>> is weird, and I don't see why. Could some one explain?
>>
>> What I really don't get is why this file,
>> http://members.westnet.com.au/ramon_et_al/files/MGAOnlyAD.csv
>> does not import correctly when this file:
>> http://members.westnet.com.au/ramon_et_al/files/MGAOnlyAC.csv
>> does? There is only one column difference, and it does not remove the 
>> columns that would create duplicate headers at an 8 column width.
>>
> I think there's an empty column at the end of the problem CSV file 
> with no header, then after that another column called Item. i.e. after 
> DateSampled there are two commas. That might be confusing the import...
>
> Regards,
> Micha
>> Problem 2.
>> Translating from MGA94z51 to GDA94 or WGS84 is successful.
>> But any of these to AMG84z51 fails silently after creating the shape 
>> file.
>>
>> Equally, AMG84z51 to any of these fails silently.
>>
>> I don't know what the problem is. If the error is logged somewhere, 
>> and someone can tell me where to look I'll hunt it down and post what 
>> it says.
>>
>> For reference I have also tried this on a test file that *only* 
>> contains the coordinates, and hence no duplicate headers at 8 
>> character width, and had the same problem.
>>
>> Problem 3.
>> Translating  using Save As also fails but gives an error.
>> Exception : forward transform of 2.11507, -0.524793 failed with 
>> error: failed to load datum shift file.
>>
>> Running from AMG84z51 to MGA94z51 gives a very similar error, except 
>> gives the numbers 2.11507, -0.525033
>>
>>
>> Does anyone have any suggestions?
>> -ramon._______________________________________________
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