CRS - projection issue on export

[John Maguire]

Hi all, and Thanks to Emma for pointing me to the group.

I'm semi-retired after a longish career in Cartography and GIS mostly in the Resources sector.

Currently working for an Environmental team using QGIS to develop Environmental Management Plans in the NT.

I've been using QGIS for a couple of years and Love it! Just scratching the surface really...

The ISSUE...I've recently encountered an issue when I, Export, "Save features as" to a .shp file with the view to changing the CRS on export. Eg. Exporting a Point file that's in  GDA94 MGA zone 53 to GDA 94 LL.

When the exported file is added to the project it loses the CRS and on inspection states the CRS is unknown. 

Has any else encountered a similar issue? ....suspect I'm missing a CRS setting in the Project or QGIS settings somewhere.... buggered if I can find it.

I'm running the latest LTR 3.40.6

Any guidance would be greatly appreciated......

Cheers

John

[Andrew Jeffrey]

Hi John,

Welcome to the group.

Can you try exporting again, but setting the CRS on export to EPSG:4283. This is the EPSG code for GDA94 LL

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[John Maguire]

Thank you Andrew...That worked!....

It would be good to know why?.   Is it to do with using the Geographic 2D CRS ?..

Is it best practice to use the Vector>Reproject tool rather than Export Save as etc?

Cheers

John

[Andrew Jeffrey]

Hi John, 

That's great.

I actually think the issue here is the shapefile format. I just did a quick test locally, and I can save to a GeoPackage format using that CRS and bring it back into QGIS no worries at all. However, when I do it with a shapefile the CRS cannot be identified and I need to set it. So it's likely something to do with the WKT in the prj file, either how it's formatted or how QGIS interprets it??

Typically, for most use cases within QGIS I would think that EPSG:4283 is the preferred CRS for GDA94 LL. But the EPSG you used is a valid EPSG code, I'm just unsure of its typical application. Someone on here who is better versed at coordinate reference systems may be able to add some detail to its use.

But glad you're up and running.

Thanks

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[Slade Beard]

Hi All,

My query here is somewhat "sideways".. Due to some specialist work I did recently I have become aware of the errors inherent in using GDA 94 or any earlier projections for the NT (it is applicable to the rest of Australia too, with varying impacts depending on where you are working in Australia).  The consequence is that, for example, at Katherine in the NT, there is a distance of 1.8 metres to the northeast between data developed against GDA94 and the reality on the ground.

The rate of  tectonic movement of Australia to the NE is enough to create for me a significant awareness of the data sources we use a lot. For example, much of Australia's 1:100000 maps are based on AGD66... Which is 55m to the SW from the current location of geographic features in the NT. Given the density of mining leases, for example, in the NT, I have learned to maintain awareness of the projections I  am using :-) !

Cheers...

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From: australian-qg...@googlegroups.com <australian-qg...@googlegroups.com> on behalf of Andrew Jeffrey <aljef...@gmail.com>
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Subject: Re: [QGIS-Australia-User-Group] CRS - projection issue on export

 

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[box...@iinet.net.au]

Hi Slade,

 

Yes, it very important to know what and when the coordinate information was collected and the projection in which it has been reported.

 

The accuracy issue is a product of different location techniques. Hand held GPS are only accurate to 5 – 10 m, maybe  1- 2 m with SOUTHPAN SBAS enabled. Ground survey and differential GPS data will be more accurate.

 

Cheers Grant

The ISSUE...I've recently encountered an issue when I, Export, "Save features as" to a .shp file with the view to changing the CRS on export. Eg. Exporting a Point file that's in  GDA94 MGA zone 53 to GDA 94 LL.

When the exported file is added to the project it loses the CRS and on inspection states the CRS is unknown. 

 

Has any else encountered a similar issue? ....suspect I'm missing a CRS setting in the Project or QGIS settings somewhere.... buggered if I can find it.

I'm running the latest LTR 3.40.6

 

Any guidance would be greatly appreciated......

 

Cheers

John

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