[Gvsig_english] BIG problems with reprojecting AGD66 to GDA94

Mon Nov 30 04:30:36 CET 2009

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.