AutoCAD Civil 3D

[#1]

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.

[#2]

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

[#3]

we tried changing the UCS, it doesnt really work.

[#4]

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

[#5]

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8peaches wrote:

we tried changing the UCS, it doesnt really work.

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Did you try what I advised, sir?

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

[#6]

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.

[#7]

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.

[#8 · Accepted solution]

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.

[#9 · Accepted solution]

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.

[#10 · Accepted solution]

Drawing attachment