LKS-92 koordināšu pārrēķins uz platuma un garuma grādiem.

lks-92.php

<?php

// Ja šis nedod korektu rezultātu Y asī, atkomentē rindiņu, kur ir "$y -= -6000000.0;" 

function LKSToLatLon($x, $y)
{
    /* Ellipsoid model constants (actual values here are for WGS84) */
    $UTMScaleFactor = 0.9996;
    $sm_a = 6378137.0;
    $sm_b = 6356752.314;
    $x -= 500000.0;
    // Pirmā atšķirība no WGS84 - Kilometriņš šurpu, kilometriņš turpu.
    // Ja šis nedod korektu rezultāt, atkomentē sekojošo rindiņu. 
    // $y -= -6000000.0;
    $x /= $UTMScaleFactor;
    $y /= $UTMScaleFactor;
    // Otrā atšķirība no WGS84 - Centrālais meridiāns ir citur.
    $lambda0 = deg2rad(24);
    /* Precalculate n (Eq. 10.18) */
    $n = ($sm_a - $sm_b) / ($sm_a + $sm_b);
    /* Precalculate alpha_ (Eq. 10.22) */
    /* (Same as alpha in Eq. 10.17) */
    $alpha_ = (($sm_a + $sm_b) / 2.0)
        * (1 + (pow($n, 2.0) / 4) + (pow($n, 4.0) / 64));
    /* Precalculate y_ (Eq. 10.23) */
    $y_ = $y / $alpha_;
    /* Precalculate beta_ (Eq. 10.22) */
    $beta_ = (3.0 * $n / 2.0) + (-27.0 * pow($n, 3.0) / 32.0)
        + (269.0 * pow($n, 5.0) / 512.0);
    /* Precalculate gamma_ (Eq. 10.22) */
    $gamma_ = (21.0 * pow($n, 2.0) / 16.0)
        + (-55.0 * pow($n, 4.0) / 32.0);
    /* Precalculate delta_ (Eq. 10.22) */
    $delta_ = (151.0 * pow($n, 3.0) / 96.0)
        + (-417.0 * pow($n, 5.0) / 128.0);
    /* Precalculate epsilon_ (Eq. 10.22) */
    $epsilon_ = (1097.0 * pow($n, 4.0) / 512.0);
    /* Now calculate the sum of the series (Eq. 10.21) */
    $phif = $y_ + ($beta_ * sin(2.0 * $y_))
        + ($gamma_ * sin(4.0 * $y_))
        + ($delta_ * sin(6.0 * $y_))
        + ($epsilon_ * sin(8.0 * $y_));
    /*  Precalculate ep2 */
    $ep2 = (pow($sm_a, 2.0) - pow($sm_b, 2.0))
        / pow($sm_b, 2.0);
    /* Precalculate cos (phif) */
    $cf = cos($phif);
    /* Precalculate nuf2 */
    $nuf2 = $ep2 * pow($cf, 2.0);
    /* Precalculate Nf and initialize Nfpow */
    $Nf = pow($sm_a, 2.0) / ($sm_b * sqrt(1 + $nuf2));
    $Nfpow = $Nf;
    /* Precalculate tf */
    $tf = tan($phif);
    $tf2 = $tf * $tf;
    $tf4 = $tf2 * $tf2;
    /* Precalculate fractional coefficients for x**n in the equations
       below to simplify the expressions for latitude and longitude. */
    $x1frac = 1.0 / ($Nfpow * $cf);
    $Nfpow *= $Nf;   /* now equals Nf**2) */
    $x2frac = $tf / (2.0 * $Nfpow);
    $Nfpow *= $Nf;   /* now equals Nf**3) */
    $x3frac = 1.0 / (6.0 * $Nfpow * $cf);
    $Nfpow *= $Nf;   /* now equals Nf**4) */
    $x4frac = $tf / (24.0 * $Nfpow);
    $Nfpow *= $Nf;   /* now equals Nf**5) */
    $x5frac = 1.0 / (120.0 * $Nfpow * $cf);
    $Nfpow *= $Nf;   /* now equals Nf**6) */
    $x6frac = $tf / (720.0 * $Nfpow);
    $Nfpow *= $Nf;   /* now equals Nf**7) */
    $x7frac = 1.0 / (5040.0 * $Nfpow * $cf);
    $Nfpow *= $Nf;   /* now equals Nf**8) */
    $x8frac = $tf / (40320.0 * $Nfpow);
    /* Precalculate polynomial coefficients for x**n.
       -- x**1 does not have a polynomial coefficient. */
    $x2poly = -1.0 - $nuf2;
    $x3poly = -1.0 - 2 * $tf2 - $nuf2;
    $x4poly = 5.0 + 3.0 * $tf2 + 6.0 * $nuf2 - 6.0 * $tf2 * $nuf2
        - 3.0 * ($nuf2 * $nuf2) - 9.0 * $tf2 * ($nuf2 * $nuf2);
    $x5poly = 5.0 + 28.0 * $tf2 + 24.0 * $tf4 + 6.0 * $nuf2 + 8.0 * $tf2 * $nuf2;
    $x6poly = -61.0 - 90.0 * $tf2 - 45.0 * $tf4 - 107.0 * $nuf2
        + 162.0 * $tf2 * $nuf2;
    $x7poly = -61.0 - 662.0 * $tf2 - 1320.0 * $tf4 - 720.0 * ($tf4 * $tf2);
    $x8poly = 1385.0 + 3633.0 * $tf2 + 4095.0 * $tf4 + 1575 * ($tf4 * $tf2);
    /* Calculate latitude */
    $lat = $phif + $x2frac * $x2poly * ($x * $x)
        + $x4frac * $x4poly * pow($x, 4.0)
        + $x6frac * $x6poly * pow($x, 6.0)
        + $x8frac * $x8poly * pow($x, 8.0);
    /* Calculate longitude */
    $lon = $lambda0 + $x1frac * $x
        + $x3frac * $x3poly * pow($x, 3.0)
        + $x5frac * $x5poly * pow($x, 5.0)
        + $x7frac * $x7poly * pow($x, 7.0);
    return Array(rad2deg($lat), rad2deg($lon));
}

Varbūt kādam noder online konvertors, kurš uzreiz ļauj konvertēt vairākus punktus: http://map.lgia.gov.lv/index.php?lang=2&cPath=2&txt_id=8 .

LKS92 -> DMS ir "x,y(LKS-92 TM) > B,L".

Thank you so much, @laacz, for sharing this code publicly! May publish the same logic in Python?

Also, does anyone know, which coordinate system they use at Jānu Sēta? As you may notice, that mention LKS coordinate system:

But for sharing links they use another system, which I cannot figure out:
https://www.balticmaps.eu/lv/c___2449589.65-7768051.29-16/bl___cl

@soshial, yes, you can. As for URL scheme - I have no clue.