Does anyone know how to make new CRS to reproject some old plans?

Question

I need to reproject some old Cadastral plans, but I can't find any appropriate CRS on web.

• They are in old Hungarian System (Budapest tangent plane stereographic projection) which used in late XIX and beginning XX century for topographical survey.
• The central point was marked inside old observatory on Gellert Hill, Budapest. The ellipsoidal coordinates of central point: φ=47°29'9.6380"north and λ=19°02'56.9441" east of Greenwich.
• Used ellipsoid was Bessel and axis were oriented to south-west.
• There's no falsing values (some points have negative coordinates).
• I have few points in this stereo-sys, and also in Gauss-Kruger 6 zone MGI for Balkan projection:

pt.num|_______ Ygk|________Xgk|_____Ystereo |   Xstereo|
  1494| 6584836,63| 5059846,65|     -2826,78| 201119,03|
  1033| 6580079,58| 5057131,79|      1967,28| 203771,57|
  960 | 6582258,96| 5061971,45|      -276,39| 198960,07|

Note that axis are set to Y← and X.↓

Has anyone any hints to solve this?

Answer 1

Check out this paper, A budapesti sztereografikus, illetve a régi magyarországi hengervetületek és geodéziai dátumaik paraméterezése a térinformatikai gyakorlat számára, by Gábor Timár, Gábor Molnár, and Gergely Márta.

At the end, they list these parameters:

The Hungarian Civil Stereographic projection:
Ellipsoid: Bessel 1841
Datum: HD1863
Projection type: Oblique Stereographic
Longitude of projection center: 19° 2' 56.9441"
Latitude of projection center: 47° 29' 9.6380"
False Easting of the projection center: 0
False Northing of the projection center: 0
Scale factor: 1
Orientation: SW

The transformation from HD1863 to WGS84 is given on page 17. The method is Coordinate Frame.

dx = 595.75 m
dy = 121.09 m
dz = 515.40 m
rx = -8.226"
ry = 1.5193"
rz = -5.541"
scale = -7.371 ppm

So. If you're using Esri software, I would try using the Double Stereographic projection rather than Stereographic. Stereographic is used in the US mainly. Other software may use different names.

You may also have to change the SW orientation to EN. I think in the SW system, y = westing and x = southing. To switch to x/easting, y/northing, change the signs of both values and swap the axes. Thus,

x/southing = +12345.1 > y/northing = -12345.1
y/westing = -12345.1 > x/easting = +12345.1