[postgis-users] transform - update lake set the_geom=transform(the_geom, 26971)

[cyw at dls.net]

I have a table city which contains Multipolygons (SRID=4326) in latitude and 
longitude. To project it to  a plane coordinate (SRID=26971), I did:

    update lake set the_geom=transform(the_geom, 26971);

It ran without any error. But some of the resulted values in the_geom column 
became null or empty.

Any hitnts why it did this?

Before the transformation, I viewed the table with QuantumGIS, it looked OK. 
Afterwards, QuantumGIS showed nothing.

Thanks,
CYW