tkifle
Posts: 3
Joined: Mon Oct 19, 2009 10:20 am

transform

Wed Oct 21, 2009 6:36 pm

I am trying the following and I am not getting the correct numbers :
from UTM Zone 31N(European 1950) x=494868 y=6764990
to UTM Zone 31N(WGS84) I get x=494777.75 y=6764774.23
I was expecting x=494776.75 an y=6764774.27
What am I doing wrong?

User avatar
johan
GpsGate
Posts: 14695
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: transform

Thu Oct 22, 2009 12:43 am

CoordTrans uses 7-parameter Helmert transformation. This means that Datums older than 1970 are a little bit inexact. E.g. European 1950, which is from 1950.

Regards,
Johan

Franson Support

tkifle
Posts: 3
Joined: Mon Oct 19, 2009 10:20 am

RE: transform

Thu Oct 22, 2009 1:06 am

I don’t understand, I am able to choose from ED50 to wgs84, then how come it is not inexact?

Regards
T

User avatar
johan
GpsGate
Posts: 14695
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: transform

Thu Oct 22, 2009 1:22 am

When measuring the land you do an approximation the Earth is an ellipsoid. But before 1970 (and the laser) people doing measurements made errors.

7-parameter Helmert demands a perfect approximation.

Regards,
Johan

Franson Support

tkifle
Posts: 3
Joined: Mon Oct 19, 2009 10:20 am

RE: transform

Thu Oct 22, 2009 9:59 am

I am using ESRI engin to compare with CoordTrans, Do you know if ESRI use the same?

Regards
T

User avatar
johan
GpsGate
Posts: 14695
Joined: Wed Aug 04, 2004 10:40 pm
Location: Sweden
Contact: Website

RE: transform

Thu Oct 22, 2009 10:52 am

That is one of the options yes. There are many ways and standards to transform coordinates.

Regards,
Johan

Franson Support

Return to “CoordTrans”