[PROJ] Proj 6 API questions

Nyall Dawson nyall.dawson at gmail.com
Tue Mar 19 03:00:56 PDT 2019 

On Tue, 19 Mar 2019 at 15:36, Kristian Evers <kreve at sdfe.dk> wrote:
>
>
>
> > On 19 Mar 2019, at 02:19, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> >
> > On Mon, 18 Mar 2019 at 20:19, Kristian Evers <kreve at sdfe.dk> wrote:
> >>
> >> Instead of using the acronym you can just use the parameters from
> >> proj_ellipsoid_get_parameters() directly, so that
> >>
> >>     +ellpsg=GRS80
> >>
> >> becomes
> >>
> >>    + a=6378137.0  +rf=298.257222101.
> >>
> >> For both your use cases that should work fine. You will of course have
> >> to do a bit of string manipulation to achieve this.
> >
> > I'm a little confused by some of the results I'm seeing here. Eg:
> >
> >> bin/projinfo -o all "Airy 1830"
> >
> > PROJ string:
> > +ellps=airy
> >
> > WKT2_2015 string:
> > ELLIPSOID["Airy 1830",6377563.396,299.3249646,
> >    LENGTHUNIT["metre",1],
> >    ID["EPSG",7001]]
> > ...
> >
> > Looks good. But if I try querying EPSG:7001, I get
> >
> >> bin/projinfo -o all "EPSG:7001"
> >
> > input string: parsing of user string failed: crs not found
> >
> > Shouldn't that give the same results as searching by name?
> >
>
> From the projinfo docs:
>
> "where {object_definition} or {object_definition} is a PROJ string, a WKT string,
> an object name or a AUTHORITY:CODE (where AUTHORITY is the name of a
> CRS authority and CODE the code of a CRS found in the proj.db database)."
>
> You are giving a authority:code combination so it is only looking for a CRS. With
> the -k switch you can change that behaviour to look for a operation instead.
>
> Maybe there’s a need for more options to the -k switch? Like ellipsoid, axis, AoU
> and so on?

Thanks for the explanation. I'd say, yes, the ability to query
ellipsoid/etc by code would be handy. But most of all I'd like to see
an "all" option, which would list everything with the matching code.
That'd be handy when you have a code alone, and no idea what type of
object it represents....

Nyall

>
> > Nyall
> >
> >
> >
> >
> >
> >
> >
> >>
> >> /Kristian
> >>
> >> -----Oprindelig meddelelse-----
> >> Fra: PROJ <proj-bounces at lists.osgeo.org> På vegne af Nyall Dawson
> >> Sendt: 18. marts 2019 10:40
> >> Til: Kristian Evers <kreve at sdfe.dk>
> >> Cc: PROJ <proj at lists.osgeo.org>
> >> Emne: Re: [PROJ] Proj 6 API questions
> >>
> >> On Mon, 18 Mar 2019 at 17:34, Kristian Evers <kreve at sdfe.dk> wrote:
> >>>
> >>> I may be wrong but I don’t think there are acronyms for them. It’s based
> >>> on the EPSG dataset and acronyms are not assigned in that regime. Do
> >>> you actually need them or is this just so that it fits better in existing QGIS
> >>> infrastructure?
> >>
> >> There's two things QGIS uses this for:
> >>
> >> 1. When a user selects the CRS for their project, the project
> >> ellipsoid (used when calculating geodetic distances/areas for the
> >> project) is automatically set to match the ellipsoid corresponding to
> >> this CRS. i.e. select EPSG:28356 and the project ellipsoid is set to
> >> GRS80, set it to EPSG:102013 and you get International 1909.  So we
> >> need a way to get the ellipsoid from an acronym (or alternatively,
> >> directly from a CRS).
> >>
> >> 2. When performing geodetic distance/area calculations, QGIS
> >> transforms coordinates from the layer's source CRS to a crs crafted
> >> from "+proj=longlat +ellps=XXXXX +nodefs", and then uses the result
> >> when performing the geodetic calculations. So we need a way to obtain
> >> the ellipsoid acronym given an ellipsoid definition (where a
> >> corresponding one exists).
> >>
> >> (Full disclaimer: I'm not fully aware of the background behind this
> >> logic, and there may be superior logic to follow. Let me know if you
> >> think there is!)
> >>
> >> Nyall
> >>
> >>
> >>>
> >>> We could potentially assign acronyms for all ellipsoids but I fear that will
> >>> become a maintenance mess whenever the EPSG dataset is updated.
> >>>
> >>> /Kristian
> >>>
> >>>> On 18 Mar 2019, at 08:27, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> >>>>
> >>>> On Mon, 18 Mar 2019 at 16:56, Kristian Evers <kreve at sdfe.dk> wrote:
> >>>>>
> >>>>> You use proj_get_authorities_from_database() for that. Generally there’s functions
> >>>>> for retrieving all info like that, just search around in the function reference a bit and you’ll
> >>>>> find it.
> >>>>
> >>>> Ok, that part is working, and I'm seeing a LOT more! But now I'm a bit
> >>>> confused... if I use this approach to iterate through the ellipsoids,
> >>>> is there anyway to get the ellipsoid acronym from them? Using
> >>>> proj_list_ellps I could get PJ_ELLPS->id.
> >>>>
> >>>> Nyall
> >>>>
> >>>>
> >>>>
> >>>>>
> >>>>> /Kristian
> >>>>>
> >>>>> On 18 Mar 2019, at 07:52, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> >>>>>
> >>>>> On Mon, 18 Mar 2019 at 16:42, Kristian Evers <kreve at sdfe.dk> wrote:
> >>>>>
> >>>>>
> >>>>> Hi Nyall,
> >>>>>
> >>>>> I am very happy to see that you have started working on this!
> >>>>>
> >>>>> You will probably get less discrepancies between the QGIS list of ellipsoids
> >>>>> and the PROJ equivalent if you instead use proj_get_codes_from_database
> >>>>> using type PJ_TYPE_ELLIPSOID.
> >>>>>
> >>>>>
> >>>>> What should I use as auth_name if I want to get ALL ellipsoids? The
> >>>>> dox state it must not be null...
> >>>>>
> >>>>> Thanks for the detailed pointers, I'll let you know the result!
> >>>>>
> >>>>> Nyall
> >>>>>
> >>>>>
> >>>>> You should then be able to get the
> >>>>> parameters with proj_ellipsoid_get_parameters. This is untested on my part
> >>>>> but I believe that is the general workflow you have to go through to get the
> >>>>> ellipsoid out of proj.db.
> >>>>>
> >>>>> proj_list_ellps() simply shows you the same list as you would get from calling
> >>>>> `proj -le`, i.e. ellipsoids that can be used with `+ellps=xxx` parameters. This
> >>>>> is confusing and I shall think of a way to change the docs so it is less confusing :-)
> >>>>>
> >>>>> It would be interesting to see the difference between the ellipsoid tables from
> >>>>> The QGIS and PROJ databases.
> >>>>>
> >>>>> /Kristian
> >>>>>
> >>>>> On 18 Mar 2019, at 04:39, Nyall Dawson <nyall.dawson at gmail.com> wrote:
> >>>>>
> >>>>> Hi list,
> >>>>>
> >>>>> So (thanks for sponsorship from the ICSM), I'm working on porting QGIS
> >>>>> to the Proj 6 API. I suspect I'll have many more questions (especially
> >>>>> as I attempt to drop QGIS' own custom projection database in favour of
> >>>>> the upstream proj one). Let's get started...
> >>>>>
> >>>>> I thought I'd begin with a simple task of replacing QGIS' ellipsoid db
> >>>>> with proj's, using proj_list_ellps(). QGIS has this table of
> >>>>> "standard" ellipsoids, built up from... somewhere... in the vast
> >>>>> history of the QGIS project. When comparing against proj's db, it
> >>>>> includes many items which are missing in proj's:
> >>>>>
> >>>>> Adrastea2000: Adrastea2000 10000.0/7000.0
> >>>>> Amalthea2000: Amalthea2000 125000.0/64000.0
> >>>>> Ananke2000: Ananke2000 10000.0/10000.0
> >>>>> Ariel2000: Ariel2000 581100.0/577700.0
> >>>>> Atlas2000: Atlas2000 18500.0/13500.0
> >>>>> Belinda2000: Belinda2000 33000.0/33000.0
> >>>>> Bianca2000: Bianca2000 21000.0/21000.0
> >>>>> Callisto2000: Callisto2000 2409400.0/2409300.0
> >>>>> Calypso2000: Calypso2000 15000.0/8000.0
> >>>>> Carme2000: Carme2000 15000.0/15000.0
> >>>>> Charon2000: Charon2000 593000.0/593000.0
> >>>>> IGNF:ELG004: Clarke 1866 6378206.4/6356583.799998981
> >>>>> IGNF:ELG003: Clarke 1880 Anglais 6378249.1453/6356514.8698
> >>>>> IGNF:ELG010: Clarke 1880 IGN 6378249.2/6356514.999978254
> >>>>> cape: Clarke 1880 mod. 6378249.145/6356514.966398753
> >>>>> Cordelia2000: Cordelia2000 13000.0/13000.0
> >>>>> Cressida2000: Cressida2000 31000.0/31000.0
> >>>>> Deimos2000: Deimos2000 7500.0/5200.0
> >>>>> Desdemona2000: Desdemona2000 27000.0/27000.0
> >>>>> Despina2000: Despina2000 74000.0/74000.0
> >>>>> Dione2000: Dione2000 560000.0/560000.0
> >>>>> Earth2000: Earth2000 6378140.0/6356750.0
> >>>>> Elara2000: Elara2000 40000.0/40000.0
> >>>>> Enceladus2000: Enceladus2000 256300.0/244600.0
> >>>>> Epimetheus2000: Epimetheus2000 69000.0/55000.0
> >>>>> Europa2000: Europa2000 1564130.0/1560930.0
> >>>>> Galatea2000: Galatea2000 79000.0/79000.0
> >>>>> Ganymede2000: Ganymede2000 2632400.0/2632350.0
> >>>>> Helene2000: Helene2000 16000.0/16000.0
> >>>>> Himalia2000: Himalia2000 85000.0/85000.0
> >>>>> Hyperion2000: Hyperion2000 164000.0/107000.0
> >>>>> IGNF:ELG108: IAG GRS 1967 6378160.0/6356774.5161
> >>>>> IGNF:ELG037: IAG GRS 1980 6378137.0/6356752.314140356
> >>>>> Iapetus2000: Iapetus2000 718000.0/718000.0
> >>>>> IGNF:ELG001: International-Hayford 1909 6378388.0/6356911.9461279465
> >>>>> Io2000: Io2000 1829400.0/1815700.0
> >>>>> Janus2000: Janus2000 97000.0/77000.0
> >>>>> Juliet2000: Juliet2000 42000.0/42000.0
> >>>>> Jupiter2000: Jupiter2000 71492000.0/66854000.0
> >>>>> Larissa2000: Larissa2000 96000.0/96000.0
> >>>>> Leda2000: Leda2000 5000.0/5000.0
> >>>>> Lysithea2000: Lysithea2000 12000.0/12000.0
> >>>>> Mars2000: Mars2000 3396190.0/3376200.0
> >>>>> Mercury2000: Mercury2000 2439700.0/2439700.0
> >>>>> Metis2000: Metis2000 21500.0/21500.0
> >>>>> Mimas2000: Mimas2000 209100.0/191400.0
> >>>>> Miranda2000: Miranda2000 240400.0/232900.0
> >>>>> Moon2000: Moon2000 1737400.0/1737400.0
> >>>>> Naiad2000: Naiad2000 29000.0/29000.0
> >>>>> Neptune2000: Neptune2000 24764000.0/24341000.0
> >>>>> Nereid2000: Nereid2000 170000.0/170000.0
> >>>>> Oberon2000: Oberon2000 761400.0/761400.0
> >>>>> Ophelia2000: Ophelia2000 15000.0/15000.0
> >>>>> IGNF:ELG017: PLESSIS 1817 6376523.0/6355862.933255573
> >>>>> Pan2000: Pan2000 10000.0/10000.0
> >>>>> Pandora2000: Pandora2000 55000.0/31000.0
> >>>>> Pasiphae2000: Pasiphae2000 18000.0/18000.0
> >>>>> Phobos2000: Phobos2000 13400.0/9200.0
> >>>>> Phoebe2000: Phoebe2000 115000.0/105000.0
> >>>>> Pluto2000: Pluto2000 1195000.0/1195000.0
> >>>>> Portia2000: Portia2000 54000.0/54000.0
> >>>>> Prometheus2000: Prometheus2000 74000.0/34000.0
> >>>>> Proteus2000: Proteus2000 218000.0/201000.0
> >>>>> Puck2000: Puck2000 77000.0/77000.0
> >>>>> Rhea2000: Rhea2000 764000.0/764000.0
> >>>>> Rosalind2000: Rosalind2000 27000.0/27000.0
> >>>>> IGNF:ELG032: SPHERE PICARD 6371598.0/6371598.0
> >>>>> Saturn2000: Saturn2000 60268000.0/54364000.0
> >>>>> Sinope2000: Sinope2000 14000.0/14000.0
> >>>>> Telesto2000: Telesto2000 15000.0/7500.0
> >>>>> Tethys2000: Tethys2000 535600.0/525800.0
> >>>>> Thalassa2000: Thalassa2000 40000.0/40000.0
> >>>>> Thebe2000: Thebe2000 58000.0/42000.0
> >>>>> Titan2000: Titan2000 2575000.0/2575000.0
> >>>>> Titania2000: Titania2000 788900.0/788900.0
> >>>>> Triton2000: Triton2000 1352600.0/1352600.0
> >>>>> Umbriel2000: Umbriel2000 584700.0/584700.0
> >>>>> Uranus2000: Uranus2000 25559000.0/24973000.0
> >>>>> Venus2000: Venus2000 6051800.0/6051800.0
> >>>>> IGNF:ELG052: WGS72 6378135.0/6356750.520016094
> >>>>> IGNF:ELG102: WGS72 (NWL-10F) 6378135.0/6356750.520016094
> >>>>> IGNF:ELG053: WGS84 6378137.0/6356752.314245179
> >>>>>
> >>>>> The vast majority of these are planetary ellipsoids/moons, but there's
> >>>>> others which are less obvious (cape/IGNF*). So
> >>>>>
> >>>>> Question 1: should the non-Earth ellipsoids be included in the proj database?
> >>>>>
> >>>>> Question 2: What about cape/IGNF* ? Should they be included in proj,
> >>>>> or are they mistakes and should not even be included in the current
> >>>>> QGIS db?
> >>>>>
> >>>>> Nyall
> >>>>> _______________________________________________
> >>>>> PROJ mailing list
> >>>>> PROJ at lists.osgeo.org
> >>>>> https://lists.osgeo.org/mailman/listinfo/proj
> >>>>>
> >>>>>
> >>>>> _______________________________________________
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> >>>>>
> >>>>>
> >>>
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