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If your lat/long is -37.7072, 144.967 then you are south of the equator (you provided a negative latitude). Your 'high value' longitude indicates you are circumventing the equator to a location that's almost on the opposite side of the prime meridian (almost halfway around the world). I'm guessing your site is in, or near, Australia.
You are able to move back and forth between ArcGIS and Civil3D because both programs can understand coordinate systems and both are capable of transforming between geographic coords and projected coords. Moving back and forth between ArcGIS (or C3D) and 3DSMax may seem like a good good idea but you must exercise caution when doing so. The most important thing when moving between programs are the UNITS of the coordinate system.
While both ArcGIS and C3D can understand projected x,y's used in coodinate systems that use meters, they can also understand geographic lat/long coordinates that use degrees. Both programs are capable of transforming from meters to degrees and vice-versa. This means when you assign a coordinate system that uses meters to C3D modelspace, then input data such as lat/long coordinates in degrees, C3D will calculate the given lat/longs coords to the equivalent x,y coords. Civil3D is essentially transforming a known point from degrees to meters.
Q: Will the coordinates -37.7072, 144.967 and the coordinates -37.7072, 144.967 pinpoint the exact same spot on Earth?
A: Maybe, maybe not. It all depends on the units. If one pair of coords is lat/long degrees and the other pair in meters, then no. Give identical pairs of numbers, a lat/long point will not be located at the same spot as an x,y point.
Q: Can Civil3D distinguish between lat/long coordinates and x,y coordintes?
A: Yes, it can, but only if you know how to input, or feed, the coordinate data into C3D.
Q: Can 3DSMax distinguish between lat/long coordintes and x,y coordinates?
A: AFAIK, no. The program doesn't understand lat/long degrees. If you give it 144.967 degrees it will treat it as 144.967 meters.
<<.....but what I really want is for the World UCS to be at my lat lon point as this would be a much cleaner solution.>>
In C3D, ArcGIS and all other geospatial capable programs, the Lat/Long coord system, such as LL84, is a 'World' coordinate system (yes, LL 84 is a global coord system) that uses units of degrees, not meters. In 3DSMax, you must use meters (or mm) because 3DSMax isn't capable of understanding lat/long degrees.
You need to convert your lat/long coords into your corresponding MGA grid which uses meters. Once converted, you can then use those coords in 3DSMax. The actual conversion from degrees to meters must occur prior to doing your work in 3DSMax. Yes, the numbers in the coordinate system will be large, but they will be geospatially sound and exporting to a format understood by C3D will now be accurate.
Chicagolooper
That's a very good explanation of how things can happen with coordinates. More detailed than I could write without a lot of thought. The only thing I thought might be missing (or I may have missed it) was that the Lat/Long system is a spherical system. What we work in with Civil 3D is a rectilinear system. All grids are rectangles and when you add elevation you get cubes. When you add elevation to Lat/Longs you get pyramids truncated by spheres.
My point is that the transformation from spherical to rectilinear is just that. A transformation. A projection. Distances will be different. Working in a small area you won't see much of that.
If you do a lot of transformations, back and forth multiple times. I would think you'd start to see errors cause by rounding.
I'm not much of an expert. I don't do it very much. But I find it fascinating to think about.
We live and work on a spinning spheroid circling a star that's moving through a galaxy, etc.
Allen Jessup
CAD Manager - Designer
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NP,
"If I set the map point
at 0,0 before bringing in a shape file, the background map behaves as
desired, but thrn when i import a shape file it is in the wrong place (it doesn't know about the transpose)."
Got just the thing for you. You can create a Custom Projection with an Affine Post-Processor for either Transverse Mercator or Lambert Conformal Conic Projections. Translate, Rotate, Scale, the works.
Alan Gilbert shows basics >>>Here<<<. For a Deep Dive look >>>Here<<<.
You only other option is the Transformation Tab, which breaks Bing and most Map Commands.
Dave
Dave Stoll
Las Vegas, Nevada
NVIDIA Quadro P5000 16GB
Windows 10 Pro 64 / Civil 3D 2024
NP,
Attached, please find 2 drawings, one in MGA-55 and a Custom Coordinate System that should be what you're looking for. Also included is a Shapefile of Moreland-North and a Point Shapefile of -37.7072,144.967 Origin.
If you also need to Rotate and Scale, that's no problem, but you'll need 3 matching points to get parameters.
Dave
Dave Stoll
Las Vegas, Nevada
NVIDIA Quadro P5000 16GB
Windows 10 Pro 64 / Civil 3D 2024
@nano_langenheim wrote:
<<Civil also allows the placing of a point through the geolocation tools in
lat long format and to specify the datum those coordinates come from (I may
be doing this incorrectly).>>
Contrary, to popular belief, the geolocation tool is tricky to use and not a good way to assign your coordinate system to modelspace. Here's an easier way:
- Open a brand-new, clean metric template (or imperial if applicable) then use MAPCSASSIGN to search for, select, and assign an appropriate coordinate system. In your case, you are using the MGA coordinate system, meters.
- Using your mouse wheel, zoom-out until you see the red geomarker (looks like a red bicycle wheel with red spokes). Center the geomarker in the middle of your monitor using the pan function.
- Turn on Bing Hybrid. Using the image as your guide, use your mouse to zoom-in and pan to your area of interest. Even if you turn OFF Bing imagery, your drawing is still accurately georeferenced against the coordinate system you elected to use in step 1.
What do the steps 1 through 3 mean? It means your drawing units are in meters and your x,y coordinates are accurately referenced against the MGA grid. Why meters? Because your AutoCAD drawing units inherit the same units as the assigned coordinate system. In your case, the Map Grid of Australia (MGA), uses meters.
Despite your assigned coordinate system using meters, you can, if you know how, input lat/long degrees in Civil3D. C3D will calculate the new x,y coordinate in meters from the original lat/long degrees. This calculation and geospatial position taken from a global system using Lat/Longs degrees to your modelspace’s coordinate system that’s using meters is called a Transformation.
If you must do design work in 3DSMax, convert or transform all your Lat/Long degrees into MGA grid meters using Civil3D or another program capable of undertaking transformations. Do this first, before doing your 3DSMax design work. Don’t rely on 3DSMax to perform your coordinate transformations. It doesn’t understand Lat/Long geometry. Once transformed, you can move back and forth between C3D and 3DSMax because the units, which are meters, are understood in both programs and this makes exports and imports accurate.
One final note, if you design in 3DSMax you must draw in meters, not mm and not cm. (You must force 3DSMax to adopt, or inherit, the ‘drawing units’ of the MGA grid.) So, when drawing in 3DSMax, 7mm must be entered as 0.007 and 7cm must be entered as 0.07. If you enter 7mm in 3DSMax simply as ‘7’ then it will be 7 meters when exported to Civil3D and not 0.007meters as you originally intended.
Chicagolooper
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