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Ian
268 post(s)
#17-May-17 22:00

I have been supplied some DXF files from a CAD program but I cant overlay them in my project. I can open them on their own but there are issues with the assign projection. Previously I have used NZMG and this has been fine (same supplier) but its not working this time. The only info the supplier has given me is that they use Mt Eden datum but don't know about the projection. I have never used a CAD program so have no idea how they work regarding projection info. Can anyone enlighten me?

Thanks

rockland
97 post(s)
#17-May-17 22:33

In the USA, specifically in Alabama, where I am, many of the coal companies have created detailed AutoCAD mine maps. They used the NAD27 and/or NAD83 coordinate systems on the area topo maps....BUT did not assign their AutoCAD maps with the proper projection; it just imports as orthographic. I realized several years ago that when I imported the AutoCAD maps of the mines that I knew the coordinates to be in NAD27 AL West though Manifold just saw it as orthographic. Its an easy fix to assign the coordinate system to the proper projection. Plus there are ways to change all the different files into the proper projection at one time. A person still has to do some editing which seems usual when importing dwg files. I hope this helps a little or gives a clue to this issue and a resolution.

Ian
268 post(s)
#17-May-17 22:39

I thought I knew the projection as i have used it before with the MT Eden coordinates but its not working this time so wondered if its something from their end. I was unable to import DWG files into manifold thats why I got the supplier to use DXF. Don't know enough about these file formats to know why one works and one doesn't.

tjhb
10,094 post(s)
#17-May-17 23:12

If you want a second pair of eyes to have a look and you have data you can share (here or via email) then just say.

The first thing I would do is to work out where the point (0, 0) would fall, by extrapolating coordinates from known location(s).

tjhb
10,094 post(s)
#18-May-17 01:00

Ian,

Thanks for the files.

Using Assign Projection, press the Load from file button (top left) and point to the attached .xml file, which defines the Mt Eden 2000 projection, using parameters from the official LINZ definition in NZGD2000 Merdiional Circuits.

This lines up, but please make your own checks.

Tim

Attachments:
Mt Eden 2000.xml

tjhb
10,094 post(s)
#18-May-17 01:30

There are some binary representation artefacts in the .xml definition.

If you liked you could adjust these to use more "pure" values--though I think they would be adjusted back to the nearest binary approximation internally. (So no practical difference.)

Currently

<scaleX>9.999000000000000100000000e-001</scaleX>

<scaleY>9.999000000000000100000000e-001</scaleY>

<centerLat>-3.687972222222219900000000e+001</centerLat>

<centerLon>1.747641666666669900000000e+002</centerLon>

Could adjust these to

<scaleX>9.999000000000000000000000e-001</scaleX>

<scaleX>9.999000000000000000000000e-001</scaleX>

<centerLat>-3.687972222222222222222222e+001</centerLat>

<centerLon>1.747641666666666666666667e+002</centerLon>

adamw


10,447 post(s)
#18-May-17 08:12

The third and fourth numbers are actually materially cleaner (the corrections are one digit too early to be lost to 53-bit mantissa).

Log from Radian command window:

--SQL

> ? CAST('9.999000000000000100000000e-001' AS FLOAT64)

float64: 0.9999

> ? CAST('9.999000000000000100000000e-001' AS FLOAT64)

  = CAST('9.999000000000000000000000e-001' AS FLOAT64)

boolean: 1 -- same

> ? CAST('-3.687972222222219900000000e+001' AS FLOAT64)

float64: -36.8797222222222

> ? CAST('-3.687972222222219900000000e+001' AS FLOAT64)

  = CAST('-3.687972222222222222222222e+001' AS FLOAT64)

boolean: 0 -- different

> ? CAST('1.747641666666669900000000e+002' AS FLOAT64)

float64: 174.764166666667

> ? CAST('1.747641666666669900000000e+002' AS FLOAT64)

  = CAST('1.747641666666666666666667e+002' AS FLOAT64)

boolean: 0 -- different

(My comments appear after --.)

Ian
268 post(s)
#18-May-17 01:55

Thanks Tim. I can't download the file though, it just opens when I click on it

tjhb
10,094 post(s)
#18-May-17 02:03

What browser are you using? Can't you right-click the link then select "Save link as"--that's for Firefox. Other browsers should be similar.

Attached version has the "purer" numbers.

Also sent by email.

Attachments:
Mt Eden 2000.xml

Ian
268 post(s)
#18-May-17 02:24

Done, works perfectly, thanks for your help Tim

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