Why do I get large transformation parameters when I want to do a 5-parameter Helmert transformation of 2 local 2D coordinate systems in CoordTrans? Identical points in both systems differ by 2-3cm, and the obtained transformation parameters move along the axes by 100-1000m.Parametars
Source system
Target System

Hi Marko,

in some cases, the centre of rotation is not inside but outside the network. This appears to be the case here. The cause is therefore your data or the configuration of your points.

/Micha

Hi Micha

I have sent you my data, all the points are in the rectangle 15m x 270m. It is not clear to me why the center of rotation and translation would be outside that rectangle, especially since the differences between the two coordinate systems are small.
When I use say Leica Geo Office, I get normal transformation parameters of 2-3 cm.

Hi Marko,

When I use say Leica Geo Office, I get normal transformation parameters of 2-3 cm.

The different is the functional model. Most applications use a simplified functional model treating only the coordinates of the target system as observations. In JAG3D's CoordTrans both, the coordinates of the source and the target system, are treated as observations. CoordTrans addresses the most general case. So if you compare your results with other applications, make sure that all applications use identical algorithms.

/Micha

Hi Marko,

I have sent you my data,

I now had the time to take a look at the coordinates. Everything looks fine from my point of view. If you reduce your coordinates manually, the shift will be small. However, it is still the identical transformation, i.e. the weighted sum of squared residuals is (almost) identical, i.e., 5.84452183E-4 (reduced systems) vs. 5.84452188E-4 (original data). I'm not sure about your expectations, but large shift values are not an indicator of a poor transformation.

Kind regards
Micha

Here the reduced systems:

source.txt

R1.1 955.748 841.856  
R1.2 939.741 817.587  
R1.3 910.947 775.604  
R1.5 851.444 694.252  
R1.6 820.398 653.913  
R1.7 795.972 622.823  
R2.2 945.373 813.856  
R2.3 916.452 771.794  
R2.5 887.125 730.827  
R2.6 856.820 690.199  
R2.7 825.676 649.768  
R2.8 806.988 625.956  
R2.9 801.188 618.639  
R3.2 961.670 827.155  
R3.3 955.949 818.512  
R3.4 950.564 810.361  
R3.5 944.833 801.852  
R3.6 938.964 793.273  
R3.7 933.380 785.106  
R3.8 927.523 776.679  
R3.9 921.676 768.296  
R3.10 915.895 760.139  
R3.11 909.990 751.821  
R3.12 903.919 743.374  
R3.13 898.169 735.395  
R3.15 892.114 727.108  
RN3.16 885.988 718.766  
RN3.17 880.078 710.800  
RN3.18 873.926 702.550  
RN3.19 867.727 694.275  
RN3.20 861.766 686.406  
RN3.21 855.612 678.318  
RN3.22 849.293 670.068  
RN3.23 843.276 662.206  
RN3.24 836.977 654.123  
RN3.25 830.632 645.939  
RN3.26 824.575 638.168  
R3.27 818.297 630.220  
R3.28 811.868 622.091  
R3.29 806.107 614.799  

target.txt

R1.1 955.779 841.828 
R1.2 939.767 817.559 
R1.3 910.969 775.580 
R1.5 851.444 694.232 
R1.6 820.392 653.889 
R1.7 795.966 622.804 
R2.2 945.399 813.829 
R2.3 916.466 771.778 
R2.5 887.139 730.809 
R2.6 856.814 690.181 
R2.7 825.687 649.747 
R2.8 806.978 625.935 
R2.9 801.193 618.618 
R3.2 961.700 827.123 
R3.3 955.980 818.480 
R3.4 950.591 810.331 
R3.5 944.860 801.824 
R3.6 938.987 793.245 
R3.7 933.406 785.081 
R3.8 927.544 776.651 
R3.9 921.698 768.270 
R3.10 915.915 760.115 
R3.11 910.007 751.793 
R3.12 903.935 743.348 
R3.13 898.182 735.376 
R3.15 892.128 727.088 
R3.16 885.972 718.752 
R3.17 880.063 710.789 
R3.18 873.907 702.536 
R3.19 867.705 694.259 
R3.20 861.750 686.395 
R3.21 855.593 678.301 
R3.22 849.275 670.056 
R3.23 843.259 662.192 
R3.24 836.989 654.103 
R3.25 830.616 645.928 
R3.26 824.557 638.152 
R3.27 818.280 630.203 
R3.28 811.852 622.074 
R3.29 806.090 614.780