How to align Map Units and Drawing Units?

[Anonymous]

Hi there, 

I'm an AutoCAD newbie- so pardon me if I don't use the correct terminology. This is my problem:

Currently, I am writing an AutoLisp routine to export geographical coordinates of each point- of each entity- in each layer- in my drawing (GeoJSON).

Everything works fine however except it seems that my drawing units do not match my map units 1:1

I especially notice this issue when measuring distances in AutoCAD, and then measuring distances in Google Maps.

Here I am measureing the distance between two streets, my resulting measurement is 132885.6715 millimeters (approx. 133 meters)Here I am conducting the same measurement and as you can see the resulting value is 93.46 metersHere is how my Drawing units are set up.

At this point.. I feel like I've messed something up in my setup of AutoCAD or my geolocation data. I would Imagine that once you have a geographic location in AutoCAD that I'd be able to conduct real world measurements. 

Any pointers on where I could have gone wrong are very very very appreciated, or if more information is required- I can provide it. 

Thanks!

[pbejse]

Not sure, try  looking into -dwgunits

Command: -DWGUNITS

Drawing units:
  1. Inches
  2. Feet
  3. Millimeters
  4. Centimeters
  5. Decimeters
  6. Meters
Unit for length <2>: 

 also measurement variable

[Anonymous]

Here is my result from that:

[pbejse]

Apologies, was reading about GeoJSON.

Anyway, did you try and change the value to 6 and scale the objects?

[Anonymous]

That unfortunately didn't work. 

I also tried using the DI command to measure the distance .. but it's still giving me the scaled value. Is there a way to get the scale factor of the drawing? I've calculate the difference between the measurements in AutoCAD and the real world measurements and arrived at about 0.7 

[Anonymous · Accepted solution]

I think I figured out the measurement inaccuracy issue. I was selecting WGS84.PseudoMercator  as the projection always, rather than using a local projection. Once I used the nearest projection, the measurements were accurate. 

https://knowledge.autodesk.com/support/autocad/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/AutoC...

~~

If the GIS coordinate system assigned to the drawing is not appropriate for the geographic location you set, measurements taken on the map may not be accurate.

Because the earth is not perfectly round, no single geographic coordinate system is able to accurately define all locations on the surface of the Earth. Consequently, various organizations define local coordinate systems, where measurements are taken locally from a local datum.

Local coordinate systems are considered more accurate because they align more closely with the Earth's surface in that locality, in comparison to an Earth-centric datum. Often, more than one coordinate system may cover the location you are interested in. As a general rule of thumb, the coordinate system with its datum closest to that location is considered to be the most accurate.

If measurements on the map are not accurate, change the GIS coordinate system of the drawing to a local coordinate system with a datum closer to your location.

[pbejse]

---

@Anonymous wrote:

I think I figured out the measurement inaccuracy issue. I was selecting WGS84.PseudoMercator  as the projection always ........ 

.. If measurements on the map are not accurate, change the GIS coordinate system of the drawing to a local coordinate system with a datum closer to your location.

---

Well there you go. Glad you figure it  out eventually, Thank you for sharing.

Not sure what it means though.