<div dir="ltr">Any AutoCAD drawing <i>can</i> be on real world coordinates. They're often not because no real world coordinates were readily available for the project and there wasn't a compelling need for real world coordinates. AutoCAD Map3D and subsequent versions with different names like "Civil 3D" have support for coordinate system conversions, but that doesn't mean that a DWG/DXF that was produced in vanilla AutoCAD can't be on a real world coordinate system.<div><br></div><div>AutoCAD is always Cartesian projected coordinates (not spherical geography) so you can open a DXF into a QGIS project and then use the QGIS move tool to move it onto whatever reference data you have in the project. The AutoCAD data might be in different units that you need but you can take a guess and use the QGIS scale tool. A common problem in the USA is an AutoCAD file that's in inches but your project is in feet. So scaling by 12 fixes that. And QGIS has a rotate tool that allows for aligning different "norths". So with the three QGIS tools move, scale and rotate you can do an affine transformation. Maybe not as accurate or as clean as you might hope for, but it's a solution that I've used many many times.</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Nov 21, 2021 at 11:59 AM Nicolas Cadieux <<a href="mailto:njacadieux.gitlab@gmail.com">njacadieux.gitlab@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="auto">Hi,<div><br><div>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.<br><br><div dir="ltr">Nicolas Cadieux<div><a href="https://gitlab.com/njacadieux" target="_blank">https://gitlab.com/njacadieux</a></div></div><div dir="ltr"><br><blockquote type="cite">Le 21 nov. 2021 à 13:52, Bernd Vogelgesang <<a href="mailto:bernd.vogelgesang@gmx.de" target="_blank">bernd.vogelgesang@gmx.de</a>> a écrit :<br><br></blockquote></div><blockquote type="cite"><div dir="ltr">
<br>
<div>On 21.11.21 15:35, Nicolas Cadieux
wrote:<br>
</div>
<blockquote type="cite">Hi,
<br>
<br>
.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.
<br>
<br>
Nicolas
<br>
</blockquote>
<p>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.</p>
<p>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.<br>
<br>
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.<br>
</p>
<p>Hope my dislike for this "technology" was not too obvious ;)<br>
</p>
<p>Cheers,</p>
<p>Bernd</p>
<p><br>
</p>
<blockquote type="cite">
<br>
On 2021-11-21 9:07 a.m., Greg Troxel wrote:
<br>
<blockquote type="cite">Boaz Bar Ilan<a href="mailto:boazprosie@gmail.com" target="_blank"><boazprosie@gmail.com></a>
writes:
<br>
<br>
<blockquote type="cite">i always have problem importing dwg or
dxf . the layers dont fit the
<br>
coardinations and even when i set the layers crs it doesnt
work.
<br>
</blockquote>
I am far from an expert, but recently tried to deal with a dwg.
<br>
<br>
My impression is that they are almost always in local
coordinates, and
<br>
the path to success is something like using GeoScience plugin to
define
<br>
a local CRS based on control points where you know global
coordinates
<br>
and local, and then to use that CRS for the data.
<br>
<br>
I recently imported some "PNEZD" data (csv with point it,
northing,
<br>
easting, vertical, and description, all in an unspecified local
grid,
<br>
from a total station data collector) and used geoscience to
align it
<br>
wtih RTK obsservations of a few points, and things fit quite
well.
<br>
<br>
How are you getting dwg? Are you using the proprietary dwg
library with
<br>
gdal, or is there some open source path?
<br>
<br>
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<br>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail_signature"><div dir="ltr">Richard W. Greenwood<br><a href="http://www.greenwoodmap.com" target="_blank">www.greenwoodmap.com</a></div></div>