Something looks wrong with the coordinate transformation system in MapInfo
(I checked with 4.5.2).
We are frequently using in Belgium the Lambert Conformal Conic projection
with 2 parallels, a very common projection;
the coordinate system is known to MapInfo as Belgium National System 72 and
is defined in MapInfow.prj.
The origin (decimal degrees) is: lon 4.3569397222, lat 90.
What troubles me is the following: I expect any point which lies on the
central meridian to have exactly the same false easting as
the origin (which is located by definition on this central meridian), hence
here 150000.01256 m.
This is not at all what I obtain in MI.
This can be shown by the following code (it can be entered in the MB window
or compiled and executed).
The code creates 4 points, all along the central meridian; one of them is
the origin.
Then the projected coordinates are computed and displayed in a browser,
reproduced below
lon, lat, x, y
4.3569397222 90.0000000000 150000.0125599951 5400088.4377999976
4.3569397222 50.0000000000 149243.8167470680 76456.3790686473
4.3569397222 49.0000000000 149228.0895242284 -34777.6272560041
4.3569397222 51.0000000000 149259.6728815702 187693.0925382139
So when executed, a 700 m error is shown to take place. I cannot believe my
eyes.
What is happening ? Thanks for any help.
MB Code is:
Create Table "Belg72" (lon Decimal(20,10),
lat Decimal(20,10),
x Decimal(20,10),
y Decimal(20,10))
File "C:\Belg72.TAB" TYPE NATIVE Charset "WindowsLatin1"
Create Map For Belg72 CoordSys Earth Projection 1, 0
Insert into Belg72 (lon, lat) Values(4.3569397222,90)
Insert into Belg72 (lon, lat) Values(4.3569397222,50)
Insert into Belg72 (lon, lat) Values(4.3569397222,49)
Insert into Belg72 (lon, lat) Values(4.3569397222,51)
Update Belg72 Set Obj=CreatePoint(lon, lat)
Set CoordSys Earth Projection 19, 110,
"m", 4.3569397222, 90, 49.8333333333, 51.1666666667,
150000.01256, 5400088.4378000004
Update Belg72 Set x=Centroidx(obj), y=Centroidy(obj)
Browse * from Belg72
Pierre Henrotay
Siemens Nixdorf Information Systems
Major Projects
Tel.: +32 81 559 687
Fax: +32 81 559 658
Mail (office): [EMAIL PROTECTED]
Mail (home): [EMAIL PROTECTED]
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