Gauss Kruger to WGS84

Question

I have to transform Gauss Kruger coordinates to WGS84 in my software application. I'm using the Java library of PROJ4 to do that.

For Gauss Kruger, I always use EPSG:31466 and for WGS84 EPSG:4326. When I compare my transformations with the results of some online coordinate transformation tools, I realized that for points outside EPSG:31466 (Gauss Kruger zone 2) I get different results.

Given only the Gauss Kruger coordinates, how can get the same results as the online tools?

Is this possible without additional information?

I have no experience with coordinate systems.

Answer 1

Did you define the towgs84 parameters, if yes which set you are using? Whiteout parameters the difference can grow up to 230m.

In relation to transformation with gridshift (beta2007), i detect the following possible differences

|name        |min                    |avg                  |max               |
-------------------------------------------------------------------------------
|beta2007    |  0.0                  |   0.0               |   0.0            |
|none        | 99.250366063551       | 168.54883882139686  | 229.80965234792  |
|DHDN 1995   |  0.0039479794869021   |   1.3881561638417907|   5.3941602247576|
|DHDN 2001   |  0.0012488505338594   |   1.1313220611228276|   4.4184600531721|
|DHDN middle |  0.0063214990593368   |   1.4902204047890757|   5.7135874379391|
|DHDN north  |  0.0062192022064108   |   2.383577943992589 |   9.6145778026886|
|DHDN south  |  0.0025021389171325003|   1.9607273460804975|   7.7021706883189|
|PD/83       |  0.0066647722696291   |   1.1689030241033365|   5.7448426426863|
|RD/83       |  0.006001788797633601 |   1.6276119718489253|   6.0123640601873|
|boundless   |  0.01218811866022     |   1.6378737326663775|   6.0457296947613|
|proj4js     |  0.0029917728718977   |   3.682670211383219 |   9.6418722378787|

The transformation descriptions are here, the boundless parameter here, proj4js just use by default a 3 parameter set.

de_dhdn_2001   = 598.1,   73.7, 418.2,  0.202,  0.045, -2.455,   6.7
de_dhdn_1995   = 582.0,  105.0, 414.0,  1.04,    0.35,  -3.08,   8.3
de_dhdn_north  = 590.5,   69.5, 411.6, -0.796, -0.052, -3.601,  8.30
de_dhdn_middle = 584.8,   67.0, 400.3,  0.105,  0.013, -2.378, 10.29
de_dhdn_south  = 597.1,   71.4, 412.1,  0.894,  0.068, -1.563,  7.58
de_pd83        = 599.4,   72.4, 419.2, -0.063, -0.022, -2.723,  6.46
de_rd83        = 612.4,   77.0, 440.2, -0.054,  0.057, -2.797,  2.55
de_4283        =  24.9, -126.4, -93.2, -0.063, -0.247, -0.041,  1.01
boundless      = 612.4,   77.0, 440.2, -0.054,  0.057, -2.797,  0.5259752559300956
proj4js        = 606.0,   23.0, 413.0,  0.0,    0.0,    0.0,    0.0

If you don't use the gridshift method, you should use the de_dhdn_2001 Parameter set for whole Germany.