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Coordinates system

16 REPLIES 16
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Message 1 of 17
8peaches
8502 Views, 16 Replies

Coordinates system

Somebody, Anybody please help:smiley sad : 

 

I'm a new user of civil 3d and i have the following problem N.B i'm in South Africa

 

When i bring my points they get misplaced actually they get place on the northern side of where the drawing is meaning they are mirrored.

 

Similarly when i import an image from google earth it comes in upside down and on the northern side of where i need it to be.

 

Previously we used a program called model maker, in model maker my points go excatly to where in them to be, which is they are not mirrored. we used Lo 27 in model maker and which i also used in civil 3d but in civil 3d a get different results.

 

I believe the problem lays on my ability to set up my drawing coordinates.

 

Please help.

16 REPLIES 16
Message 2 of 17
antoniovinci
in reply to: 8peaches

Try to mirror those points around a y=x axis, sir.

Message 3 of 17
8peaches
in reply to: antoniovinci

we tried changing the UCS, it doesnt really work.

Message 4 of 17
johngordon6189
in reply to: 8peaches

what point format did you import with?  I am trying to get a handle on your point file format.  Is it point #, description, easting, northing, elevation?

 

John

John Gordon
CAD Manager/Survey Technician

C3D 2018/2020
Microstation
Windows 10
Message 5 of 17
antoniovinci
in reply to: 8peaches


8peaches wrote:

we tried changing the UCS, it doesnt really work.


Did you try what I advised, sir?

You only have to mirror those points around an axis passing thru 0,0 and 1,1

Message 6 of 17
sboon
in reply to: johngordon6189

Looking at the settings in your drawing it appears that your points are in meters and you intended to work in metric units.  However your ACad drawing units are set to Feet, so when you import the point file the coordinates are being scaled and shifted away from the proper location.

 

The more time I spend looking at the settings in this drawing the more confused I get.  There seems to be a mix of Metric and Imperial styles and label styles.  Some of the drawing settings are metric, but others are Imperial.  Looking at the drawing settings for example:

  • Drawing unit is Meters - except that the ACad units are Feet
  • Distance unit is Foot
  • Dimension unit is Inch
  • Coordinate unit is Foot
  • Grid Coordinate unit is Meter

At this point you need to stop working on this drawing if at all possible, before things get any worse.  You should find a clean OOTB template somewhere and import all of the styles and settings from it, overwriting everything in this drawing.  Then you can move forward with some assurance that things will work as expected.  You should also find the template drawing that this file was created from and trash it.

 

Steve
Expert Elite Alumnus
Message 7 of 17
jmayo-EE
in reply to: antoniovinci

I agree. If the points are simply mirrored the northing and easting were reversed during import.

 

Either mirror the points or reimport reversing the N and E in the point format. For example a PNEZD would need to be PENZD.

John Mayo

EESignature

Message 8 of 17
HansSMS
in reply to: 8peaches

Good day,

 

Apart from the drawing template issues mentioned by the posts above, the rest of the advice given in the previous posts about mirroring the input and or reversing N E point format is unfortunately wrong.

 

The coordinate system need to be set up correctly, this is what you are really after.

 

The South African coordinate system works in a Y,X system, X values increase south from the equator in meters,  the Y axis values increase moving west, ie you have a system of "Southings" and "Westings". Your drawing has tried to accomplish this  by having the numerical value of the X axis increase south but to achieve this the values have been made negative. Likewise the Y axis increases numerically to the west, in your drawing where the Y values should be negative they are positive to achieve this. The Y coordinates are negative east of the central meridian of your coordinate system, this is how they correctly appear in the text file.

 

Again the coordinate text file is set up correctly, apart from separating the triangle definitions further down the file, this should be left as is.

 

You will need to set up a UCS with the coordinates working properly, increasing positive west and south. I'll have a go at this for you over the weekend. Once this has been sorted, there should be no problem reading in the text file correctly.

 

I've attached some reading material in the meantime explaining the South African National Grid.

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018
Message 9 of 17
HansSMS
in reply to: 8peaches

OK, I've sorted out your drawing.

 

First some background: Only e few countries like South Africa and Germany have survey projections with small scale factors, so you end up surveying on projection in the field by applying a scale factor to your distances.

 

AutoCAD is designed to work in a local ground system. and connect to the projection with a transformation set up. This transformation only works between the projection coordinate system and the ground. It also assumes that everywhere in the world one uses Eastings and Northings positive increasing East and North.

 

South Africa works with a Y and X Axis, being "Westings" and "Southings". Because of the minimal scale factor, one tends to survey in the projection coordinate system for most surveys other than really high precision stuff, so you rarely run two coordinate systems.

 

I've done two things: Set up a UCS called "SA" which gets your cursor to show the same coordinates you have on your grid lines, without having the opposite sign. You can effectively draw in the LO 27 system

 

Unfortunately you can't import points into a UCS, only into WORLD coordinates or via a projection set up in the transformation tab of the drawing settings dialog. So the second thing I've done is set up a transformation from your Lo 27 system to the WORLD system, this allows you to read in the text file as "Grid Eastings/Northings", and the points plot correctly on your screen. I've taken a grid point on your site as origin and set the scale factor to unity as you are not converting from projection to ground, you are working in projection. I've also set the rotation so that you have the azimuth reading 0° south.

 

To import points I've created an import format called "PYXZD", you'll need to use this to import points into the"Grid Eastings/Northings" fields.

 

I've attached the drawing and point files. Hope this works for you. The drawing units have been fixed as well.

 

 

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018
Message 10 of 17
HansSMS
in reply to: 8peaches

Drawing attachment

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018
Message 11 of 17
8peaches
in reply to: 8peaches

Thank you Hans Moller and everyone else who offered me help.

I thank all of you from the bottom of my heart Smiley Happy

Spoiler
 
Message 12 of 17
jmayo-EE
in reply to: HansSMS

Thank you for the education, posting the solution and files Hans. Great job identifying the issue but we should leave a note for future readers. If you are not in Germany or South Africa and your points are mirrored, you most likely do have the northing and easting flipped. This is a very common mistake.

John Mayo

EESignature

Message 13 of 17
HansSMS
in reply to: 8peaches

The message I've been trying to get to Autodesk (since 2006) is that not all coordinate systems run positive East and North. One needs a facility to import cogo points into another UCS other than WORLD, rather than going through hoops  switch eastings and northings or mirroring point plots to achieve a result.

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018
Message 14 of 17
8peaches
in reply to: 8peaches

please excuse slowness

 

Here's a continuation of the previous problem, i copied the setting of the drawing you had send me to the original copy that i had when i imported the points the went to their exact position that is now solved.

 

i later took a drawing from a different project and copied its contents to the this drawing that i had set up using your settings, everything was well until i wanted to place an image from google earth, as well it went to the opposite direction and was upside down.

 

I will go for training next nonth and i'll ask some of the question there.

Message 15 of 17
HansSMS
in reply to: 8peaches

I am running Civil 3D 2013, which has lost the Google Earth functionality. Can't help you there.

 

Looking at the Durban Deep drawing you need to set up the transformation using a reference point in the middle of your site, otherwise you will pick up a scale factor problem. I doubt this will solve the GE problem though. Probably GE is looking for a UTM coordinate system. The Google Earth image will need to be re-created on the Lo 27 System, whether that's possible I don't know.

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018
Message 16 of 17
jonnoxx
in reply to: HansSMS

Just to add to this very informative thread:

 

Here is a link which gives a nice explanation of South Africa's co-ordinate system:

http://docplayer.net/13920467-An-introduction-to-coordinate-systems-in-south-africa.html

 

A thorough explanation of GIS systems:

http://web.gps.caltech.edu/gislab/HowTo/ESRI%20-%20Map%20Projections.pdf

 

And a really excellent 25-part YouTube tutorial from Autodesk aimed at 3ds Max users using Civil 3D as an initial basis for their 3ds Max project.

This has really great info for Civil 3D users in how to create, manipulate and crop surfaces and aerial photos in Civil 3D:

https://www.youtube.com/watch?v=8FKrKvEVmtQ&list=PLnKw1txyYzRli2ZElR-w9BcH8K8ltgntd

Message 17 of 17
HansSMS
in reply to: jonnoxx

The statement in this article "and no scale factor is required" is incorrect. Scale factors are less but are still there.

Hans Moller
Surveying & Management Services
Gladstone Australia
Metabox 16GB, Intel i7-9700K 3.6Ghz, 500GB SSD, 2TB HDD Nvidia GTX 1060
AutoCAD Civil 3D 2018

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