[Qgis-user] importing dwg/dxf

[Bernd Vogelgesang]

On 21.11.21 15:35, Nicolas Cadieux wrote:
> Hi,
>
> .dwg or dxf have no CRS.  They can be in inches, feet, mm, cm, m...
> Usually meter in a local CRS like a local WGS84 UTM ZONE is used.  You
> can usually find this in the metadata if available.
>
> Nicolas

I have no deep technical insight into dwg or dxf, but I am pretty sure
that those  CAD-"products" are able to be produced with valid
coordinates, fitting to a common CRS. Most people using CAD-systems
simply seem to be either too stupid for that, or just do not care.

One of the reasons, CAD-"data" is produced with a local reference system
instead with a normal CRS is, according to an CAD-operator I once asked
about this, that some CAD-systems just slow down to in-operability when
using real-world coordinates because of the huge numbers, compared to
the small coordinates in their own system.

So, I would not even try to fix this, but instead ask those guys to stop
scratching their balls and better send you proper real-world data and
tell you which CRS they are in . The handling of this "data" is
punishment enough afterwords.

Hope my dislike for this "technology" was not too obvious ;)

Cheers,

Bernd


>
> On 2021-11-21 9:07 a.m., Greg Troxel wrote:
>> Boaz Bar Ilan<boazprosie at gmail.com> writes:
>>
>>> i always have problem importing dwg or dxf .  the layers  dont fit the
>>> coardinations and even when i set the layers crs it doesnt work.
>> I am far from an expert, but recently tried to deal with a dwg.
>>
>> My impression is that they are almost always in local coordinates, and
>> the path to success is something like using GeoScience plugin to define
>> a local CRS based on control points where you know global coordinates
>> and local, and then to use that CRS for the data.
>>
>> I recently imported some "PNEZD" data (csv with point it, northing,
>> easting, vertical, and description, all in an unspecified local grid,
>> from a total station data collector) and used geoscience to align it
>> wtih RTK obsservations of a few points, and things fit quite well.
>>
>> How are you getting dwg?  Are you using the proprietary dwg library with
>> gdal, or is there some open source path?
>>
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