newbie here so please pardon me if I'm asking a silly question.

Currently I am required to work with Lat/Long coordinates in WGS84 (EPSG:4326) on QGIS for data analysis.

The input data I have comes in NZ Topo 50 Grid References and I need to transform this into WGS84 Lat/Long coordinates. The tool that I have used to do this successfully previously was the detailed online converter from LINZ found here: http://apps.linz.govt.nz/coordinate-conversion/index.aspx?Advanced=1

However, the online converter only takes in 6 figure grid references (e.g. BA32 123456) whereas I need to convert a more granular 10 figure grid reference (e.g. BA32 123.45 678.91).

Other software from LINZ that I have tried are NZMapConv and Concord. However, NzMapConv only allows up to 8 figure grid references for NZ Topo50 and does not allow bulk conversions whereas Concord does not even contain NZ Topo50 as an option (despite having support for bulk conversions).

As such, are there any tools, software, code that I may have missed that would allow me to easily do bulk conversions from NZ Topo 50 10 figure Grid References into Lat/Long coordinates for WGS84? I'm also open to trying to script my own solution but I was unable to find the algorithm or mathematical formula for the conversion.

  • Have you tried the Reproject layer tool in QGIS? It can be run as a batch process. – csk Jun 27 '18 at 19:18
  • @csk hmm I checked that out but I'm not able to do the required conversion as it only converts between coordinate reference systems whereas I need to convert the nz topo50 grid reference. Would you have any other ideas? – Martius Lim Jul 2 '18 at 2:28

Here's an update for this question since there are no other answers. I have managed (I think) to successfully convert the finer 10 figure grid references into Lat/Long coordinates in WGS84.

In short, the conversion process is as follows: NZ Topo 50 > NZTM2000 > WGS84.

To elaborate, it took me awhile but I finally realised that the NZ Topo 50 maps are based on the New Zealand Tranverse Mercator 2000 (NZTM2000) projection. Fortunately, LINZ's Online Conversion Tool for NZTM2000 is able to take in more granular coordinates, e.g. 1528677.3 5413457.7.

Since the tool is only able to take in the 6 figure grid references for NZ Topo 50, I first converted this into NZTM2000 coordinates. I then did some simple data cleaning in excel, e.g. turning 1528700.000 into 1528677.000. I then did another conversion for the NZTM2000 coordinates into WGS84 Lat/Long coordinates to get the more precise coordinates.

Leaving this question open for awhile more, please correct me if I've made a mistake somewhere!

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