- Hi !

I'm in trouble.... maybe you'll help me :

I try to write points with the mitab_c_set_points. The points coords

look like this : x=0.9432799379 y=48.2336944724... Unfortunately, once

write in the Feature, when I read this values MiAPI, from the same

file, the precision is lower : 0,943 48,234 ... which means a BIG

difference with the original points.

I tried another solution : reproject my data in a Lambert II (then the

coords are like this : x=654405 y=2254064) , but in this case, the y

value seams to be too large, and is transfomed to "1000000" for all

values...

Any advices, solution, experience ???

Thank you very much for your help

Olivier > Hi !

once>

>

> I'm in trouble.... maybe you'll help me :

>

> I try to write points with the mitab_c_set_points. The points coords

> look like this : x=0.9432799379 y=48.2336944724... Unfortunately,

> write in the Feature, when I read this values MiAPI, from the same

Olivier,

> file, the precision is lower : 0,943 48,234 ... which means a BIG

> difference with the original points.

>

> I tried another solution : reproject my data in a Lambert II (then the

> coords are like this : x=654405 y=2254064) , but in this case, the y

> value seams to be too large, and is transfomed to "1000000" for all

> values...

>

> Any advices, solution, experience ???

>

> Thank you very much for your help

>

> Olivier

>

>

You need to set the coordinate bounds when creating the file using

mitab_c_create. MapInfo uses integer values internally, and applies an

offset and multiplier to convert to/from world coordinates. Its

coordinate range is 2000 million units.

I assume your coordinates 0.943 48.234 are longitude/latitude. If you

don't set specific bounds, MapInfo assumes -180 to 180 in longitude, and

gives you only 1 million units per degree - about 0.1 metre.

If you set your bounds to cover 1 degree, MapInfo will then give you 2000

million units to that one degree, and you will get 9 decimal places. If

you set the bounds to cover 10 degrees, you will get 200 million units to

one degree, and 8 decimal places. You need to look at the range of

coordinates you need to cover, and then set appropriate bounds - which may

mean losing some precision.

I set bounds for my area (Victoria) as -28, -44, 154, 138. This gives 16

degrees, with 125 million units per degree, and this is sufficient for

millimetre precision.

When using your Lambert coordinates, you again need to calculate the range

needed to cover your area, and then set the appropriate bounds.

I hope this helps,

Chris Egan

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