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I want to use a superseded projection (NSW integrated survey datum - referred to as ISG) because my main client utilises it. The projection is based on AGD66. We regularly receive survey files in this projection and need to prepare designs in this projection.

Unfortunately no one I know, including surveyors, seems to know much about the ISG projection, let alone set up a CRS for it.

When I import ISG data into an existing QGIS file, the files reproject fine and appear in the right location. However the coordinates are obviously incorrect, making it difficult to work with.

Is there a way to extract and set a new datum based on data I know is already in ISG format?

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  • Do you have a formal definition for that datum? Creating a CRS in the right format for QGIS isn't that hard if you have the data. No data makes it hard though. – BradHards Mar 27 '14 at 11:47
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    lpi.nsw.gov.au/surveying/geodesy/projections seems to give quite a lot of information about the New South Wales ISG - Integrated Survey Grid. – nmtoken Mar 27 '14 at 12:22
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    I think you need to look at EPSG:102072 (AGD_1966_ISG_54_2), EPSG:102073 (AGD_1966_ISG_54_3), EPSG:102074 (AGD_1966_ISG_55_1), EPSG:102075 (AGD_1966_ISG_55_2), EPSG:102076 (AGD_1966_ISG_55_3), EPSG:102077 (AGD_1966_ISG_56_1), EPSG:102078 (AGD_1966_ISG_56_2), and EPSG:102079 (AGD_1966_ISG_56_3) – nmtoken Mar 27 '14 at 12:47
  • Hi User27874, are you able to advise how to get these CRS in QGIS? I cant seem to find it in the CRS section of QGIS. – boberdorf Mar 28 '14 at 3:53
  • The page @nmtoken had linked to is now moved to spatialservices.finance.nsw.gov.au/surveying/geodesy/… – AndreJ Sep 5 '17 at 8:20
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The QGIS user manual shows how to work with projections, see http://qgis.org/en/docs/user_manual/working_with_projections/working_with_projections.html. In this instance you need to follow the Custom Coordinate Reference System section.

Of course for you to do this you need to know what the proj4 parameters are for the CRS you wish to create.

Looking at the NSW Map projections page (specifically the section on ISG - Integrated Survey Grid) and the linked page to Australian Geodetic Datum 1966 (AGD66), can I think take you most of the way...

For example AGD66 is based on the Australian National Spheroid 

Semi-major axis (a):  6 378 160.0 metres
Semi-minor axis (b):  6 356 774.719 metres
Flattening (f):       1/298.25

In proj4 syntax these are:

+a=6378160.0 +b=6356774.719 +f=298.25

Looking at at the ISG - Integrated Survey Grid information we have:

Projection:             Transverse Mercator
Zone Width:             2 degrees
Longitude of Origin:    Central Meridian of each zone
Latitude of Origin:     Equator (zero degrees)
False Easting:          300 000
False Northing:         5 000 000
Central Scale Factor:   0.99994
Units:                  Metre
Ellipsoid:              ANS

In proj4 syntax these are:

+proj=tmerc +lat_0=0 +k_0=0.999940 +x_0=300000.000000 +y_0=5000000.000000 +ellps=ANS
+units=m  +lon_0=[Central Meridian of each zone]

So now you just need to figure out how many zones there are and their central meridians, for that we can take a look at the Manual of the New South Wales Integrated Survey grid Table 1 (below image).

Zones of the Integrated Survey Grid, New South Wales

Putting that all together, for example ISG zone 54_2, gives us I think:

+proj=tmerc +lat_0=0 +lon_0=141 +k_0=0.999940 +x_0=300000.000000 +y_0=5000000.000000 +ellps=ANS +a=6378160.0 +b=6356774.719 +f=298.25 +units=m +no_defs  no_defs <>

You could call this CRS any name you like, but elsewhere I have seen it called EPSG:102072 or AGD_1966_ISG_54_2.

I should stress that I am not a projection expert, so you should probably double check I haven't produced a clanger here (for example you should look at the proj4 syntax PROJ.4 - General Parameters, but certainly this is where I would start.

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    The ellipsoid definition shoud be similar to EPSG:4202: +proj=longlat +ellps=aust_SA +towgs84=-117.808,-51.536,137.784,0.303,0.446,0.234,-0.29 +no_defs. The towgs84 parameter is important, because the AGD ellipsoid has an offset to WGS84. The codes 102072 to 102079 are not really EPSG codes, but build by ESRI. They are not part of the standard CRS database used by QGIS. – AndreJ Mar 28 '14 at 12:21
  • Whilst looking at this question I came across permalink.gmane.org/gmane.comp.gis.gdal.devel/6658 which suggests that the proj4 definitions for AGD66 <EPSG 4202> are wrong and should be instead: +proj=longlat +a=6378160 +rf=298.250000000055 +towgs84=-129.193,-41.212,130.73,-0.246,-0.374,-0.329,-2.955 +no_defs no_defs. – nmtoken Mar 28 '14 at 13:13
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    EPSG has 19 different datum shifts to offer for AGD66 to WGS84. You get the 200m offset mentioned on the mailing list only when you take none of them. The offset between the others is less than 10m. There is a ntv2 grid too for cases when high precision is needed. – AndreJ Mar 28 '14 at 13:43
  • Thank you all for your generosity in sharing your knowledge, in particular user27874 for that detailed answer. That has solved my problems. I used your projection and imported some data that I knew was in the ISG format and it lined up perfectly. I could check because the data was in tiles whose file names was the coordinates of the information. – boberdorf Mar 29 '14 at 10:28
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    PLEASE NOTE, as per Andre's advice, this projection needs to have +towgs84 parameters added. Therefore, for ISG zone 54_2, you should use +proj=tmerc +lat_0=0 +lon_0=141 +k_0=0.999940 +x_0=300000.000000 +y_0=5000000.000000 +ellps=aust_SA +a=6378160.0 +b=6356774.719 +f=298.25 +units=m +towgs84=-117.808,-51.536,137.784,0.303,0.446,0.234,-0.29+no_defs no_defs <> – boberdorf Apr 7 '14 at 11:30

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