[Gdal-dev] OGR returns wrong floating values for shapefiles (and integer as real, in error)

[Mateusz Loskot]

Maciej Sieczka wrote:
> Hi,
> 
> ogrinfo (and other apps based on OGR, eg. OpenEV, QGIS) returns wrong
> floating point values querying my shapefiles. Eg.:
> 
> $ ogrinfo -al -q streams.shp
> 
> Layer name: streams
> OGRFeature(streams):523
>   CAT (Real) =         484
>   LCAT (Real) =          73
>   Z (Real) =      101.583309999999997
>   Z_BREACH (Real) =      101.583309999999997
>   Z_BREACH1 (Real) =      100.583309999999997
>   LENGTH (Real) =        2.036246000000000
>   LINESTRING (598549.144524969975464 5677309.376777020283043,598550.0
> 5677311.224603090435266)
> 
> 
> After opening the dbf in oocalc 2.03, I can see the values should
> recpectively be:
> 
> CAT	  484
> LCAT	  73
> Z	  101.58331
> Z_BREACH  101.58331
> Z_BREACH1 100.58331
> LENGTH	  2.036246
> 
> Why the spurious "09999999997" in case of Z, Z_BREACH, Z_BREACH1 in
> OGR? Note that, interestingly, LENGTH is OK though.

As Roger has explained, this is *only* a view, a format, a way of
presentation. The underlying number is still the same, in both cases.

OGR could display these values also using scientific notation,
ie. 1.0158331e+2 or engineering notation 101.58331e+0 or with only 3
decimal places 101.583.
In all these cases it's still a way of displaying, no data is
truncated or extended.

Cheers
-- 
Mateusz Loskot
http://mateusz.loskot.net