Export image has incorrect coordinates

[nano_langenheim]

Hi there,

I have tried this from both Civil3D and standard AutoCAD. I have tried both 2018 and 202 AutoCAD. I'm in Australia which may be impacting this since there is a transition to GDA2020.

I am exporting an image as a Geotiff using Raster Designer which I would like to then import into a GIS platform (QGIS)

Here is my process in standard AutoCAD:

01) Attach an image (using reference dialogue)

02) Set the geographic position using Insert menu - set location from Map - dropping a pin and selecting coordinate system MGA 55 to GDA94 (epsg 28355). (Lat -37.817, long 141.967 ish)

03) Open Raster Tools - export image as a tiff and I enter the epsg code for the file horizontal coordinate system

04) The image can be brought into QGIS - but I cannot make it appear in the right place (it is off the West Coast of Africa).

04) When I open the world file coming out of Raster Design with the Geotiff I have the following data:

125.72152520478357
0.00000000000000
0.00000000000000
-125.72152520478355
3163.81500374053621
141527.92832487361738

05) - I cannot make much sense of this as the above process is a workflow I have used in the past and has worked fine - but maybe I am missing a step?

It seems the exported Geotiff is in relation to an arbitrary 0,0 point .....Can anyone identify what am I doing wrong? 

Thanks!

[Ed__Jobe]

Have you assigned a coordinate system to the dwg before you import the image?

[Ed__Jobe]

In C3D, the command is MAPCSASSIGN.

[ChicagoLooper · Accepted solution]

Your steps numbered 1 through 4 are not good. Contrary to popular belief, those steps do work but they're tricky to use because it requires you to manually enter, or type in, a 'known' point, i.e. Lat/Long coordinates before, not after, you choose your coordinate system. Here's an easy way to accurately georeference modelspace against your chosen coordinate system, which in your case is MGA-55.

Start with a brand new, clean metric template. Then do this:

1. On command line MAPCSASSIGN=>In search box enter MGA-55=>Select MGA-55=>Assign Button. Image-1.
2. Using mouse wheel, zoom OUT until you see the geomarker in modelspace (Bicycle wheel w/Red spokes). Image-2. 
3. Go to Geolocation Tab=>Online Map Panel=>Change Map Off to Bing Hybrid. Next, zoom IN to Bing Hybrid. Image-3.

Image-1.

Image-2.

Image-3..

[nano_langenheim]

Thank you, I am very grateful for your clear instructions.

That has worked a treat in Civil 3D (though not in n AutoCAD vanilla as MAPCSASSIGN command is not available). 

[nano_langenheim]

Thanks for your note Ed.Jobe

MAPCSASSIGN is the command needed 

[Ed__Jobe]

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@nano_langenheim wrote:

Thanks for your note Ed.Jobe

MAPCSASSIGN is the command needed 

---

Yes, that is why I prefixed it with "In Civil3D". Its not available in plain AutoCAD. However, you could use C3D to create a template that has a cs assigned and give the template to your plain AutoCAD users.

[nano_langenheim]

Hi Jobe,

I’m most grateful for your reply and your earlier response. Initially I was doing the process in Acad Vanilla. I’m just re-reading Chicago Looper’s reply again – which I think says I could potentially do it in Acad Vanilla if I type in a known lat long after setting my Coordinate system through the geolocation map. – Though as he suggests – this might be a bit fussy in that I would need to know the lat long of my point in MGA55 (I could not just grab a lat ong point from Google Earth of Maps).
It’s interesting – I think I will probably just switch over to Civil3D altogether.

[ChicagoLooper]

You should stick to Civil3D or Map3D because, unlike vanilla Acad, both C3D and M3D have coordinate system libraries. If you have a thorough understanding of coordinate geometry, you can do it in Vanilla Cad but it's super tricky. 

You are correct when you say you'll need Google Earth Pro to do want to do it in vanilla AutoCad. The general idea is to find the coordinates of a single point in two different coordinate systems. One of those coordinate systems must be WGS84 Lat/Long. For example, if using Marvel stadium in Melbourne you'll need to know 1) the WGS84 Lat/Long degrees and 2) the x,y coordinates in meters of the MGA system for the stadium in order make your drawing georeferenced to MGA-55.

Trying doing this:

1. Get the corresponding x,y coordinates of the Lat/Long coordinates you obtained from Google Earth Pro. For example, use Marvel Stadium in Melbourne as your point. Go to >>epsg.io<<  and input the Lat/Long coordinates in WGS84 degrees and convert them to MGA-55 meters. Input Lat:-37.816562 and Long: 114.947507 then make your output MGA-55 (EPSG 28355).  Write down the new x,y results. Image-1.
2. Back in AutoCad, start the GEOGRAPHIC location command. On page 1, enter the Lat,Long degrees in the address section. Do not enter a street address, city location, use a mouse click, or use any other method to drop your pin. The pin's location must be a entered using Lat/Long numbers. The more decimals in your numbers, the more accurate your final output will be. Image-2.
3. Select MGA-55 for your coordinate system. You must change the drawing units to METERS if it has not already been changed. Image-3.
4. On the command line enter the x,y coordinates (meters) you got from the output in step 1. Under no circumstances should you click your mouse in modelspace. Use a comma to separate the x and y. Click enter. Image-4.
5. You want the top of your monitor to be north and the bottom of your monitor to be south. On the command line, enter 90 or accept the default value of 90 degrees for north direction. Click enter. Image-5.

Your drawing is now referenced to MGA-55 and your drawing units are in meters. The coordinates shown at the bottom edge of your monitor follow you cursor. As you you move your cursor, the number will change. The numbers are either absolute (Cartesian MGA-55 meters), or geographic (WGS84 Lat/Long degrees). Right click directly on the coordinates then select either absolute or geographic to switch back-and-forth.    

Image-1.

Image-2.

Image-3.

Image-4.

Image-5.

[nano_langenheim]

Hi Chicago Looper –
I can’t thank you enough for these lovely clear instructions! I will have a go at them and I will keep these instructions in a safe place in case of emergency Vanilla Cad only access.

All the best

[callanward96]

Hi @ChicagoLooper,

In my area, the image is misaligned (I know this from surveying tools) to the coordinates system. Is there a way of just shifting the image, to the right spot, without mucking with the GDA co - ords?

I followed your steps above, and got this discrepancy (Which agree's with my surveying tool).

Cheers

I might retry, with my survey gear, to calculate wgs lat/long and gda 2020 / 56 equivalent. As the error could be in the google earth imagery, and not bing maps.