View Full Version : state plane coordinates
2005-07-20, 05:25 PM
I am having trouble getting a handle on setting up C3D to deal properly with importing state plane coordinate points. If I set up a blank drawing with a template that is set with our local settings, with a transformation from grid to local coordinates, I can't seem to get the proper information to be accepted by the program and I get bogus coordinates listed. Then, if the wrong info is taken by the program, it won't let me change it to the correct numbers. For instance, if I wish to have a local coordinate start at N 10000, E 20000, it will create grid coordinates based on the projection from those coordinates. If I try to change the grid coordinates that were created to the correct values for my base point, the program refuses to accept my new values.
Another problem I have is importing points from an ascii file. The info I am importing comes from our GPS processing software and is output as grid coordinates and I can't seem to get C3D to recognize them as other than local coordinates, it then creates a grid coordinate from the grid coordinates. Is there some way to get C3D to understand that the imported points are already grid? I have tried to create a new import format that will show this but C3D won't import anything from the point file.
Thanks for any input.
2009-04-15, 02:25 PM
We have been working on a process here for the exact same thing. The issue is that an ascii import through the autocad points interface comes in as ground coords. The Coordinate Zone Transform check box in the Point File Format tells cad what coord system the point file you are importing is in. ie: Nad 27. It will not get your coords into grid correctly.
To get your grid coords in you need to set up a control fieldbook and import them into a survey network through the survey tab. The survey side works in grid while the cad side works in ground. an example on input:
NEZ 1 1000 1000 100 "TRAV 1"
NEZ 2 2000 2000 200 "TRAV 2"
When you look at the points in prospector tab you will see both ground and grid coords. Ex.
Point Northing Easting Grid Northing Grid Easting Elevation Description
1 1000.0020 1000.0020 1000.000 1000.000 100.00' TRAV 1
2 2000.0040 2000.0040 2000.000 2000.000 200.00' TRAV 2
NOTE: If points exist check the reset network on the Import Field Book dialog to change coords on both the control as well as the sideshots that were shot from them.
If you set up your drawing with Northing/Easting=Project Coordinates, then you should be able to setup the Transformation Tab so that Grid Northing and Grid Easting are your grid coordinates. This is practically impossible to do in any way EXCEPT to use two points, and let C3D calc the values it wants to use for its rotation, translation, and scaling. C3D uses these values in a very bizarre way, and they do NOT equate to the normal way we think. So the only real way to use these is to select Cogo Points that are set in your Project coordinate system, and key in the grid values for the Cogo Points. DO NOT try to set the scaling and rotation parameters yourself - that way leads to severe brain-damage.
Once you have the Transformation Tab configured the way you need it, you must then also define a new Point Import format to import grid coordinates. In the Point Formats on the settings tab, create a new Point Format (similar to the existing PNEZD, etc., formats) that uses "Grid Northing" and "Grid Easting" instead of "Northing" and "Easting". Then use the new Point Format to import your Grid coordinates; they should be translated to Project coordinates during the import.
There is more about this issue in an article I wrote, found here:
Powered by vBulletin® Version 4.1.11 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.