Coordinate System - change Units to project in GIS

[Anonymous]

Hello there,

at first: sorry for my bad English, I am not a native speaker 🙂

So my problem ist this:

I want to export a dwg to dxf and than import this in a GIS (preferring QGIS, ArcGIS ist also possible).

But the coordinates in the dwg-file are in millimeters and not in meters. So it is not possible to project them in the right way and to export them as shape-files and use them to work with it or project them in a different coordinate system.

So I hope someone can help me.

Best regards,

Juu

PS: I am using Autodesk AutoCAD 2017

[ВeekeeCZ]

Use the -DWGUNITS command to scale it. (dash included)

[Anonymous]

thanks BeekeeCZ for your fast reply. But when I type it nothing happens:

So what can I do? 

[ВeekeeCZ]

What happens if you type the entire word and press enter?

Does it bring up a window?

[Anonymous]

No really helpful window:

[ВeekeeCZ]

Is it LT?

Or whatever. Re-scale it manually.

_scale

0,0,0 as a reference point

0.001 as a scale factor.

[TerryDotson]

Even when it's scaled to meters the coordinates are still going to be RANDOM and it's not going to project to other known systems.  Keep in mind as you move forward that it may never have the quality needed to considered usable for anything more than an approximate location.

[ChicagoLooper]

You are using Plain Vanilla AutoCad, and it doesn't have the same geospatial capabilities found in Civil 3D and Map 3D to transform your coordinates correctly so they will be accurate in geospatial programs such as QGIS and ArcGIS. You will need to draw in meters, not millimeters. Using Vanilla Cad will only work with projected coordinates, not geographic coordinates. The former typically uses meters or feet while the latter typically use decimal degrees or degrees-minutes-seconds. 

You, or your Vanilla Cad program, will also need to know about coordinate geometry which involves using a datum and projections. A projection's origin can vary from coordinate system to coordinate system . If you ignore the nuances of your chosen projection, you'll have accuracy issues when you import or export your points.

You will have better success if you use Civil 3D or Map 3D, not Vanilla Cad, especially if you are using Lat/Long coordinates.

[Anonymous]

Thanks for that, but I know this option. Unfortunately this does not solve my problem.
This will change the unit of the drawing objects but not the coordinate system. I don't know why.

So I think the last option is to create a new coordinate system or rather a  new dwg with this coordinate systems.

Do you have experience with that? 

[ChicagoLooper]

Sorry, no. You cannot transform geospatial coordinates using Vanilla Cad. You need to use either AutoCad Map3D or Civil3D.

Beware, this forum, the Vanilla AutoCad forum, will not give you correct GIS information. You need to go to the Map3d forum.  

[ragetli]

When you are exporting to DWG, in the settings of the export you can pick your unit type, by default it is set to millimeters. Assuming you are in Revit and exporting to dwg.

[jameslammu]

Solution:

1. if using vanilla CAD:

choose units eg. meters

2. create a rectangle eg 10 m by 10m and set it to the origin point 0,0 - if its not at that point you can set by the move tool then choose bottom base then #0,0

note origin point is sometimes called null - the beginning of X and Y

3. click on insert location choose Bing maps

4. VERY IMPORTANT:

in address bar click write:

0,0

hit return

and click drop marker there

5. on GIS coordinate system choose:

WORLD MERCATOR WGS84 3857

this corresponds to BING maps (its projection is flat)

6. make sure ortho snap cursor is on and other snaps are on so that it highlights the corner of the rect

7. click on end point

and draw up should show a dashed orange line click up from origin point and release

note your origin point on this projection is in west African cost below Nigeria I believe

8. now find the spot on the earth you want to draw on

9. save your layer (no need to save the rectangle) as DXF eg as 2010 version (I save objects eg via WBLOCK pick base point!)

10. open QGIS add BING map on same CRS WIORLD MERCATOR WGS84 3857

11. drop your dxf

12. if above is correct result will be precisely same point on the map

13. want to set project CRS QGIS - for OSGB (UK) I had no problem changing it to EPSG 2700

(note project change not map projection!)

still unsure please feel free to ask

[ChicagoLooper]

@jameslammu wrote

<<1. if using vanilla CAD:>>

I don't use vanilla CAD. I use Map3D and Civil3D, both have geospatial capabilities.

.

[jameslammu]

Sorry about that - I meant to say that vanilla CAD has capacity to allow georef as well - I think judging from several forums there seems to be some confusion about this - its straight forward hopefully now for those without Map3D and Civil3D - (I need to learn both these programmes as well) 

[ChicagoLooper]

@jameslammu 

Of course it can.......but it's clunky.

Unfortunately AutoCAD doesn't thoroughly explain the steps to georeference a drawing. Combine that with users who are unwilling to learn even if clear instructions were provided. Users are typically impatient. They want one or two clicks and done. No need to understand anything, no need to learn, just click, click and the program will read your mind and spit out good results. Like telepathic georeferencing. 

It's highly beneficial if acquire an understanding of Projected Coordinates vs. Geographic Coordinates. 

If you use AutoCAD's geographical toolset correctly the program will transform from one projection to another and your linework will land in the right spot. However, if you do it wrong, or if you only think you're doing it right when you're actually doing it wrong, then the result will seem like the the program is broken...and no, it's not broken, it's user error.

[pendean]

---

@jameslammu wrote:

... now for those without Map3D and Civil3D - (I need to learn both these programmes as well) 

---

MAP3D is free to install and use for anyone with an active AutoCAD subscription: in fact, all of these are also free to install and use with an active subscription:

Architecture
Electrical
Mechanical
MEP
Plant 3D
plus the add-on Raster Design