[Qgis-user] importing dwg/dxf

[Nicolas Cadieux]

Hi,

Only AutoCAD Map3D was a certain comprehension of what a CRS is.  To my knowledge all other Autodesk Pilotdo not used any CRS.  It is my honest opinion that AutoCAD Map is the worst attempt to make a GIS.

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 21 nov. 2021 à 13:52, Bernd Vogelgesang <bernd.vogelgesang at gmx.de> a écrit :
> 
>  
> 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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>> 
>> 
>> 
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