Conversion with EPSG_RGF93_V2B_LAMBERT_93 dosen't work for Corsica

[Terahdon]

Hi,

First, thanks a lot for this library it's working great.

But I have a problem with converting coordinates in LAMBERT_93 to latitude and longitude for CORSICA.

Here is my code :

/**
     * @throws UnknownCoordinateReferenceSystemException
     * @throws UnknownConversionException
     */
    private function fromLAMBERT_93toLatLong(string $coordxet, string $coordyet): ?Coordinate
    {
        $crs = Projected::fromSRID(Projected::EPSG_RGF93_V2B_LAMBERT_93);
        /** @var GeographicPoint $to */
        $to = $this->convert($crs, $coordxet, $coordyet);
        $to instanceof GeographicPoint ? $coordinate = $this->coordinate((string)$to->getLatitude(), (string)$to->getLongitude(), self::LAMBERT_93) : $coordinate = null;
        return $coordinate;
    }

   private function convert(Projected $crs, string $coordxet, string $coordyet): ?Point
    {
        try {
            $from = ProjectedPoint::create(
                new Metre((float)$coordxet),
                new Metre((float)$coordyet),
                null,
                null,
                $crs
            );

            $toCRS = Geographic2D::fromSRID(Geographic2D::EPSG_RGF93_V2B);
            return $from->convert($toCRS);
        } catch (UnknownCoordinateReferenceSystemException|UnknownConversionException $e) {
            $this->logger->logError($e->getMessage());
            throw $e;
        }
    }

Basically it can be reduced to :

$crs = Projected::fromSRID(Projected::EPSG_RGF93_V2B_LAMBERT_93);
        /** @var GeographicPoint $to */
        $to = $this->convert($crs, $coordxet, $coordyet);

$from = ProjectedPoint::create(
    new Metre((float)$coordxet),
    new Metre((float)$coordyet),
    null,
    null,
    $crs
);

$toCRS = Geographic2D::fromSRID(Geographic2D::EPSG_RGF93_V2B);
return $from->convert($toCRS);

The code is working for every coordinates I have (more than 20000) but not for the one from CORSICA
So it's weird because I use EPSG_RGF93_V2B and EPSG_RGF93_V2B_LAMBERT_93
Both have * Extent: France - onshore and offshore, mainland and Corsica.

The coordinates comes from an official french government datafile

coordx => '1223977.1' coordy => '6075793.1'

the source : https://www.data.gouv.fr/fr/datasets/r/98f3161f-79ff-4f16-8f6a-6d571a80fea2

the specific line with LAMBERT_93 specified

geolocalisation;2A0001335;1223977.1;6075793.1;2,ATLASANTE,100,IGN,BD_ADRESSE,V2.2,LAMBERT_93;2022-03-10

I also tried all the other lambert_93 types of coordinates.

Do you have an idea from where it could come from ?
Thanks a lot if you find a little bit of time to help me.

[Terahdon]

Well it seem to work with $ignoreBoundaryRestrictions set to true.
I'm' getting those coordinates

 {
  latitude: "41.944239739838"
  longitude: "8.7532823507679"
  coordinateType: "LAMBERT_93"
}

But I don't get why.

[dvdoug]

Well it seem to work with $ignoreBoundaryRestrictions set to true. I'm' getting those coordinates

Ah, thanks - that will help a lot in tracking this down!

Could I just check what version of the library you're using, and also whether you're using the Europe data pack or not so I can debug with the same configuration?

[dvdoug]

Hi @Terahdon

I've done a bit of digging, a few different things going on here.

1. I converted the point you specified using the official IGN tool Circe, and got the numbers below - which are different from the ones you have given as an example. So I would still like to confirm which version of PHPCoord(+any datapack) you're using please as the testing I've just done (master branch) does agree with Circe.
   

2. The reason you're having difficulty with Corsica, is because although EPSG have RGF/Lambert-93 defined to cover "France", they have the Lambert-93 conversion mechanism specified as being valid only for "France - mainland onshore". This is why PHPCoord says the conversion is out of bounds. You can see that at https://epsg.org/crs_9794/RGF93-v2b-Lambert-93.html and https://epsg.org/conversion_18085/Lambert-93.html.

I will email EPSG to point out the discrepancy and ask them if it can be fixed.

[Terahdon]

@dvdoug Yes it's my mistake, to get the result in my first comment I tested it with coordx = '1177682.07' and coordy = '6111141.87'. I mixed things up sorry.

For the numbers I gave you (coordx => '1223977.1' coordy => '6075793.1') I do get
{
latitude: "41.596016636048"
longitude: "9.27485292278"
coordinateType: "LAMBERT_93"
}

[dvdoug]

OK, great. In that case since there's no bug in the algorithm itself, only the algorithm selection (because of the incorrect boundary) please do continue using $ignoreBoundaryRestrictions for the conversions you are doing.

Because the discrepancy is now explained and understood, this is safe to do so.

[dvdoug]

OK, great. In that case since PHPCoord is doing the Lambert-93 conversion correctly, and the boundary being wrong is known and understood I recommend you keep using $ignoreBoundaryRestrictions=true. For the conversions you are doing, it is safe to do so.

[Terahdon]

Hello @dvdoug and ty for your quick answer !

In my composer.json => "php-coord/php-coord": "^4.6"

And probably not necessary but in my composer.lock =>

            {
            "name": "php-coord/php-coord",
            "version": "v4.6.1",
            "source": {
                "type": "git",
                "url": "https://github.com/dvdoug/PHPCoord.git",
                "reference": "f3ff8a09cfb12ba6d232b8147e0fb1f7ac593720"
            },
            "dist": {
                "type": "zip",
                "url": "https://api.github.com/repos/dvdoug/PHPCoord/zipball/f3ff8a09cfb12ba6d232b8147e0fb1f7ac593720",
                "reference": "f3ff8a09cfb12ba6d232b8147e0fb1f7ac593720",
                "shasum": ""
            },
            "require": {
                "php": "^7.4||^8.0",
                "symfony/polyfill-php80": "^1.18"
            },
            "require-dev": {
                "ext-json": "*",
                "ext-sqlite3": "*",
                "friendsofphp/php-cs-fixer": "^3.0",
                "nikic/php-parser": "^4.10",
                "php-coord/datapack-africa": "^1.0",
                "php-coord/datapack-antarctic": "^1.0",
                "php-coord/datapack-arctic": "^1.0",
                "php-coord/datapack-asia": "^1.0",
                "php-coord/datapack-europe": "^1.0",
                "php-coord/datapack-northamerica": "^1.0",
                "php-coord/datapack-oceania": "^1.0",
                "php-coord/datapack-southamerica": "^1.0",
                "phpunit/phpunit": "^9.5.10"
            },
            "suggest": {
                "php-coord/datapack-africa": "High-accuracy addon datapack for Africa",
                "php-coord/datapack-antarctic": "High-accuracy addon datapack for the Antartic",
                "php-coord/datapack-arctic": "High-accuracy addon datapack for the Arctic",
                "php-coord/datapack-asia": "High-accuracy addon datapack for Asia",
                "php-coord/datapack-europe": "High-accuracy addon datapack for Europe",
                "php-coord/datapack-northamerica": "High-accuracy addon datapack for North America",
                "php-coord/datapack-oceania": "High-accuracy addon datapack for Oceania",
                "php-coord/datapack-southamerica": "High-accuracy addon datapack for South America"
            },
            "type": "library",
            "extra": {
                "branch-alias": {
                    "dev-master": "4.x-dev"
                }
            },
            "autoload": {
                "psr-4": {
                    "PHPCoord\\": "src/"
                }
            },
            "notification-url": "https://packagist.org/downloads/",
            "license": [
                "(MIT and proprietary)"
            ],
            "authors": [
                {
                    "name": "Doug Wright",
                    "role": "Developer"
                }
            ],
            "description": "PHPCoord is a PHP library to aid in handling coordinates. It can convert coordinates for a point from one system to another and also calculate distance between points.",
            "homepage": "https://www.phpcoord.net/",
            "keywords": [
                "UTM",
                "coord",
                "ed50",
                "epsg",
                "gda",
                "geo",
                "grid ref",
                "latitude",
                "longitude",
                "map",
                "nad",
                "nzmg",
                "osgb36",
                "projection",
                "wgs84"
            ],
            "support": {
                "issues": "https://github.com/dvdoug/PHPCoord/issues",
                "source": "https://github.com/dvdoug/PHPCoord/tree/v4.6.1"
            },
            "funding": [
                {
                    "url": "https://github.com/dvdoug",
                    "type": "github"
                }
            ],
            "time": "2022-01-29T15:42:02+00:00"
        },

`

[dvdoug]

EPSG have released a new version of the dataset today which includes the correct boundary for Lambert-93 - I will try to get an updated PHPCoord release done this week that includes it.