[Qgis-user] Does DWG work in 3.22? - RE: importing dwg/dxf
Nicolas Cadieux
njacadieux.gitlab at gmail.com
Mon Nov 22 09:54:41 PST 2021
Hi,
The GDAL/ORG library works with Open Design Alliance Teigha library.
They have a support for R13-15, R2004, R2007, R2010, R2013 and R2018 but
since Autocad is a closed format, then all of this is basically the
result of reversed engineering. DXF is an open format so that is
easier to deal with.
I believe that the drag and drop functions for DWG and DXF uses the
libopencad drivers (and that is limited to r2000 or ACAD1015)) (at least
in QGIS 3.20) so if you did drag and drop a correct file format, then
the DWG worked.
It's my personal experience that anything past R15 (2000) will be buggy
in QGIS but you can also open those files using the project >
import/export > import layer from DWG/DXF. For some reasons, some DWG
files cannot be dragged and dropped but can be imported via the project
import function. This has the advantage of keeping the Autocad styling.
I guess this function probably uses the Open Design Alliance Teigha
library and not the libopencad drivers as it will open files that I
cannot drag and drop??? Looks like those functions are not available
via the python API nor the Processing toolbox either:(
Anyways, when that fails (about 50% of the time on very big files), I
save the DWG to DXF and that either fixes the file or makes it more
compatible with the driver. IMHO, Exporting dwg to shp file is the only
real interesting feature of AutoCAD Map3D. The last version I
regularily worked with has probably 2013-15 so maybe they have updated
the product since.
https://knowledge.autodesk.com/support/autocad/learn-explore/caas/sfdcarticles/sfdcarticles/AutoCAD-drawing-file-format.html
https://docs.qgis.org/3.22/en/docs/user_manual/managing_data_source/opening_data.html?highlight=dwg#importing-a-dxf-or-dwg-file
Nicolas
On 2021-11-21 11:06 p.m., Jeff Sonnentag wrote:
>
> Somebody must get the same quality of “engineering” that we do here. :D
>
> The last item received was in feet and aligns with California State
> Plane Zone 6, but they chopped off the first digit of both “X” and “Y”
> for everything. Who knows why. Maybe things run faster for them with
> 6 digit coordinates rather than 7 digit ones like you mentioned. (???)
>
> Anyway, when I tried the simple drag and drop into QGIS 3.22 it never
> worked. Always an error message about invalid data, even after I used
> DWG Trueview to convert it to the oldest possible versions (97/98 and
> 2000). I did manage to get it in AFTER converting the DWG to a DXF
> with an online conversion site. That DXF could be drug (I hate the
> word “dragged” – seems along the lines of “runned”) into QGIS and
> appeared OK. Export to a shapefile and then do some affine adjustment
> magic and things can be worked with.
>
> Is there a reason that a DWG can’t be dropped into QGIS 3.22 but a DXF
> can? Are there some DWG versions that just don’t work? I thought I
> got a DWG to appear OK in 3.16, but maybe I just imagined it and used
> a DXF before too. . . .
>
> *From:* Qgis-user <qgis-user-bounces at lists.osgeo.org> *On Behalf Of
> *Bernd Vogelgesang
> *Sent:* Sunday, November 21, 2021 10:53 AM
> *To:* Nicolas Cadieux <njacadieux.gitlab at gmail.com>; Greg Troxel
> <gdt at lexort.com>; Boaz Bar Ilan <boazprosie at gmail.com>
> *Cc:* qgis-user <qgis-user at lists.osgeo.org>
> *Subject:* Re: [Qgis-user] importing dwg/dxf
>
> 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>
> <mailto: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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--
Nicolas Cadieux
https://gitlab.com/njacadieux
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