[Qgis-user] CRS / reprojection problems

[Matt Boyd]

Sorry, I didn't describe the resolution in my email, just complained
quietly about something.

Somehow I'd loaded up epsg 4938, which is described as GDA94. I assumed
that was the geographic projection and it wasn't until later that I looked
at https://epsg.io/4938 and saw that it's got some odd projection going on.
I could see the meters in the projection but couldn't get past that I'd
selected GDA94. Now I dig into it a little more I can see that there's this
whole set of CRS under geocentric projections. I've either forgotten about
these or never knew.

The projection I meant to use was epsg 4283 GDA94 https://epsg.io/4283 .
Somehow in my project settings the default GDA94 projection which I've
always used had been superseded by the geocentric GDA94 and I didn't notice.

Thanks QGIS people.

Matt

On Thu, May 23, 2019 at 9:56 AM Matt Boyd <mattslists at gmail.com> wrote:

> Kosza replied to me and suggested I try epsg 4283 instead of epsg 4938
>
> Is it usual to have 2 CRS with the same name, one of which appears to be
> projected and the other not, I don't think I've seen this before. There
> still seems to be something odd about 4938, but I don't see any reason to
> use it so it shouldn't bother me.
>
> Here's where I can learn something. Does anyone know what the deal with
> this is? I can see a need for a different projections, but is there
> supposed to be a better way of naming it that I didn't pick up on, am I
> going to need to remember epsg codes form now on?
>
> Thanks
> Matt
>
> On Wed, May 22, 2019 at 11:51 PM Nicolas Cadieux <
> nicolas.cadieux at archeotec.ca> wrote:
>
>> Hi,
>> Right clicking on the layer in the layer panel and changing the
>> projection to the correct one should then fix the problem.  Tell me if it’s
>> still a problem and I will also look at the data.
>> Nicolas
>>
>> Le 22 mai 2019 à 03:34, <b.j.kobben at utwente.nl> <b.j.kobben at utwente.nl>
>> a écrit :
>>
>> Sorry to have to disagree with you, but there is something wrong with
>> your data. If I load the "lineations_GDA94" it claims to be a projected
>> data, and the units are clearly meters (numbers like -42854769,3100060 in
>> the coordinate readout). But if you check, you'd find that  QGIS thinks the
>> units are degrees:
>>
>>
>>
>> <image001.png>
>>
>>
>>
>> Treating the meter cooridnates as degrees works as long as no
>> reprojection is needed, but will mess up things when combining it with
>> other data...
>>
>>
>>
>>
>>
>> --
>>
>> Barend Köbben
>>
>>
>>
>>
>>
>> On 22/05/2019, 05:54, "Qgis-user on behalf of Matt Boyd" <
>> qgis-user-bounces at lists.osgeo.org on behalf of mattslists at gmail.com>
>> wrote:
>>
>>
>>
>> Hi Nicolas and Alexandre,
>>
>> I'm pretty sure that I've done as much as I can to make sure I haven't
>> screwed up the projections. I used to make those mistakes years ago when I
>> was first learning, lately the mistakes I've made are because I haven't
>> been paying attention... I'm pretty sure I'm paying attention this time.
>>
>>
>>
>> This is a link to some data and a qgis file I'm using as an example
>>
>>
>> https://unimelbcloud-my.sharepoint.com/:f:/g/personal/boydmc_student_unimelb_edu_au/EuUzfUvxA6NGmZOuYo8_fmkB0AvLldzBmXwq68mdwZvmcw?e=Ake4Qi
>>
>>
>>
>> lineations_MGA54_projected is the shapefile with the correctly projected
>> information layer. - Known good data
>>
>>
>>
>> If I change to a geogrpahic / unprojected coordinate system, for example
>> GDA94, this layer is not displayed and the canvas is blank.
>>
>>
>>
>> If I export the lineations_MGA54_projected data to a new file as
>> unprojected GDA94 option, the re-projected data is wrong.
>>
>>
>>
>> Thanks for your help
>>
>>
>>
>> Matt
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Tue, May 21, 2019 at 11:37 PM Nicolas Cadieux <
>> nicolas.cadieux at archeotec.ca> wrote:
>>
>> Hi,
>>
>> 99 % of the time, the data is the problem because it’s in the wrong crs.
>> Right click on the problem layer in the layer panel and change the layer
>> crs to what is should be.  Use a google or other base map from quickmap
>> plugin.  That should permit you to find the correct CRS.
>>
>> Sometimes, crs will have problems reprojecting across some latitudes or
>> longitude (like projections make for the poles).  In that case,
>> reprojecting the data using the “save as” option will solve the problem.
>>
>> Nicolas
>>
>> > Le 20 mai 2019 à 21:53, Matt Boyd <mattslists at gmail.com> a écrit :
>> >
>> > Hi QGISers,
>> > I'm having an issue with reprojecting things in QGIS.
>> > Installer OSGEO64W
>> > Latest version and LTS both have same issue.
>> >
>> > Issue:
>> > reprojection just isn't working. If I load a data set with decimal
>> degrees and another with a projected coordinate system the data (points /
>> lines / polygons) will only display if the basemap is in the same
>> projection system.
>> >
>> > This is happening across 2 PCs, (windows10) and the LTS and latest
>> versions of QGIS. Has anyone got some troubleshooting tips?
>> >
>> > Thanks
>> > Matt
>> > _______________________________________________
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>> > Qgis-user at lists.osgeo.org
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>>
>>
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