[Gvsig_english] BIG problems with reprojecting AGD66 to GDA94

Mon Nov 30 04:31:00 CET 2009

Hi Guys,

This is me progressively working through a problem...

I have established that the general reprojection tool changes coordinate 
systems not datums. It is necessary to use the transformation tool to 
shift your coordinates between datums. This said I have not been able to 
do this yet.

If I select EPSG Transformations I see the following dialog. This 
obviously allows you to  change from AGD66 to GDA94.

I have used this and nothing happens.

On closer inspection I note that both the target and source SRS are 
geographical projections, and that this option allows you to convert 
only one way. From AGD66 to GDA94, not in reverse. What confuses me is 
that the source and target SRS are around the wrong way! AGD66 is 
EPSG:4202 and GDA94 is EPSG:4283. This may be a simple miscoding of the 
titles or a cause why the transformation does not work.

Can anyone read the documents that I have provided links to and find the 
appropriate data to manually convert between AGD66-GDA94, GDA94-AGD66 in 
latitude-longitude and/or grid-coordinates? I have a feeling 
transformations are generally only done on latitude-longitude layers, is 
this the case?

Cheers Simon

Simon Cropper
Botanicus Australia Pty Ltd
PO Box 160, Sunshine, Victoria 3020.
P: 9311 5822. M: 041 830 3437.
mailto: scropper at botanicusaustralia.com.au 
<mailto:scropper at botanicusaustralia.com.au>
web: www.botanicusaustralia.com.au <http://www.botanicusaustralia.com.au>

Simon Cropper (Botanicus Australia Pty Ltd) wrote:
> Hi Guys,
>
> I have continued testing to narrows down the cause of this issue.
>
> I have done the following test.
>
> Using the attached table of reference points I have created 4 source 
> files for each of my commonly used formats. This was done by creating 
> a view in the correct projection then adding the event layer using the 
> respective X and Y values. This was then converted to a shapefile.
>
> SOURCE_AGD66_GEO_EPSG4202
> SOURCE_GDA94_GEO_EPSG4283
> SOURCE_AGD66_AMG55_EPSG20255
> SOURCE_GDA94_MGA55_EPSG28355
> SOURCE_VICGRID_AMG_EPSG3110
> SOURCE_VICGRID_MGA_EPSG3111
>
> Each source file was then converted to one of the other 5 projections 
> with no transformations. The reprojected files were then opened in the 
> appropriate view (as a default they are added to the current view, 
> which is the source view) and compared to the source files. The 
> following combinations were trialled and outcome noted. Only Zone 55 
> data kept and reprojected when the source was AMG55 or MGA55.
>
> The conclusion from this analysis is that the reprojection facility 
> works converting from one coordinate system to another BUT NOT 
> converting from one datum to another (Table 1). Depending on the 
> source datum the resulting layer is offset by approximately 200m 
> either southwest or north east from the source point.
>
> Am I misreading what the reprojection tools does? Since you can pick 
> "Datum-Coordinate System" as a source and destination, then you would 
> expect that it would convert between datums.
>
> I note that you can download a transformation grid file from one of 
> the links provided below. Is this required to be used to get the 
> reprojection to work? If so how?
>
> Again any help would be appreciated...
>
> Simon
>
> --------------------------------------------------------------------------------
> *Table 1.* table of results from checking the outcome of every 
> possible reprojection between AGD66 and GDA for the coordinate systems 
> AGD55, MGA55 and VicGrid.
>
> Those reprojections that worked
>
> AGD66_GEO_EPSG*4202*_ TO_AGD66_AMG55_EPSG*20255 - Worked*
> AGD66_GEO_EPSG*4202*_ TO_VICGRID66_AMG_EPSG*3110 - Worked*
> GDA94_GEO_EPSG*4283*_ TO_GDA94_MGA55_EPSG*28355 - Worked*
> GDA94_GEO_EPSG*4283*_TO_VICGRID_MGA_EPSG*3111 - Worked*
> AGD66_AMG55_EPSG*20255*_TO_AGD66_GEO_EPSG*4202 - Worked*
> AGD66_AMG55_EPSG*20255*_TO_VICGRID66_AMG_EPSG*3110 - Worked*
> GDA94_MGA55_EPSG*28355*_ TO_GDA94_GEO_EPSG*4283* - *Worked*
> GDA94_MGA55_EPSG*28355*_ TO_VICGRID94_MGA_EPSG*3111 - Worked*
> VICGRID66_AMG_EPSG*3110*_TO_AGD66_GEO_EPSG*4202 - Worked*
> VICGRID66_AMG_EPSG*3110*_ TO_AGD66_AMG55_EPSG*20255 - Worked*
> VICGRID94_MGA_EPSG*3111*_TO_GDA94_GEO_EPSG*4283* - *Worked *
> VICGRID94_MGA_EPSG*3111*_TO_GDA94_MGA55_EPSG*28355 - Worked*
>
> Those reprojections where the destination point was ~200m southwest of 
> original
>
> AGD66_GEO_EPSG*4202*_ TO_GDA94_GEO_EPSG*4283* - Out ~200m SW
> AGD66_GEO_EPSG*4202*_ TO_GDA94_MGA55_EPSG*28355 - *Out ~200m SW
> AGD66_GEO_EPSG*4202*_ TO_VICGRID94_MGA_EPSG*3111 - *Out ~200m SW
> AGD66_AMG55_EPSG*20255*_TO_GDA94_GEO_EPSG*4283* - Out ~200m SW
> AGD66_AMG55_EPSG*20255*_TO_GDA94_MGA55_EPSG*28355 - *Out ~200m SW
> AGD66_AMG55_EPSG*20255*_TO_VICGRID94_MGA_EPSG*3111 - *Out ~200m SW
> VICGRID66_AMG_EPSG*3110*_ TO_GDA94_GEO_EPSG*4283* - Out ~200m SW
> VICGRID66_AMG_EPSG*3110*_ TO_GDA94_MGA55_EPSG*28355 - *Out ~200m SW
> VICGRID66_AMG_EPSG*3110*_ TO_VICGRID94_MGA_EPSG*3111 - *Out ~200m SW
>
> Those reprojections where the destination point was ~200m northeast of 
> original
>
> GDA94_GEO_EPSG*4283*_TO_AGD66_GEO_EPSG*4202 - *Out ~200m NE
> GDA94_GEO_EPSG*4283*_ TO_AGD66_AMG55_EPSG*20255 - *Out ~200m NE
> GDA94_GEO_EPSG*4283*_ TO_VICGRID66_AMG_EPSG*3110 - *Out ~200m NE
> GDA94_MGA55_EPSG*28355*_TO_AGD66_GEO_EPSG*4202 - *Out ~200m NE
> GDA94_MGA55_EPSG*28355*_ TO_AGD66_AMG55_EPSG*20255 - *Out ~200m NE
> GDA94_MGA55_EPSG*28355*_ TO_VICGRID66_AMG_EPSG*3110 - *Out ~200m NE
> VICGRID94_MGA_EPSG*3111*_TO_AGD66_GEO_EPSG*4202 - *Out ~200m NE
> VICGRID94_MGA_EPSG*3111*_TO_AGD66_AMG55_EPSG*20255 - *Out ~200m NE
> VICGRID94_MGA_EPSG*3111*_TO_VICGRID66_AMG_EPSG*3110 - *Out ~200m NE
>
> Cheers Simon
>
> Simon Cropper
> Botanicus Australia Pty Ltd
> PO Box 160, Sunshine, Victoria 3020.
> P: 9311 5822. M: 041 830 3437.
> mailto: scropper at botanicusaustralia.com.au 
> <mailto:scropper at botanicusaustralia.com.au>
> web: www.botanicusaustralia.com.au <http://www.botanicusaustralia.com.au>
>
>
>
> Simon Cropper (Botanicus Australia Pty Ltd) wrote:
>> Hi Guys,
>>
>> I am having problems getting the reproject tool to work as expected 
>> with Australian Projections/Datums.
>>
>> If I create a shapefile in AGD66 then reproject the file to GDA94 
>> using the reproject tool, the points are moved but only ~20m rather 
>> than 204 metres northeast of the original position. If I use the 
>> resulting GDA94 file in the AGD66 View and tell the program, it 
>> reprojects on the fly and the points overlap.
>>
>> This shows (a) that the reproject on the fly facility works, and (b) 
>> I appear to have chosen the wrong projection.
>>
>> The problem is I have tried reprojecting northing-eastings, 
>> latitude-longitude, in EPSG and ESRI format but can't get the correct 
>> reprojection. I have been using EPSG:4202 for AGD66 geographicals, 
>> EPSG:4283 for GDA94 geographicals, EPSG:20255 for AGD/ AMG zone 55 
>> and EPSG:28355 for GDA94/MGA zone 55. I have also tried ESRI: 28355 
>> and ESRI:20255 with no luck.
>>
>> I have even downloaded the transformation grid but not been able to 
>> get this to work either.
>>
>> Can anyone help?
>>
>> Attached is a list of points in a table that are released by the 
>> local government apparently created by FME. This has the comparable 
>> coordinates in 4 commonly used projections for 160 distinct points 
>> across Victoria.
>>
>> Can anyone get the correct setting and procedure to get these points 
>> to superimpose when reprojecting on the fly and for the reproject 
>> facility to work correctly?
>>
>> I have also included some useful links to help the more industrious 
>> and knowledgeable to figure out what is wrong.
>>
>> http://www.land.vic.gov.au/Land/lcnlc2.nsf/LinkView/9B33746B3D77040F4A256A250008E70A5B923E73477D6D65CA256E5F0013D73B 
>>
>>
>> http://www.icsm.gov.au/icsm/gda/gdatm/
>>
>> http://www.icsm.gov.au/icsm/gda/gdatm/gdav2.3.pdf
>>
>> Any help would be appreciated as I am trying to tick this off my list 
>> of things gvSIG can do, and was surprised to see when resulting 
>> reprojected files were compared to external reference documents they 
>> did not align.
>>
>> Any help would be greatly appreciated.