Hi
Can anyone help me with this?
I need to change cordinate sytem from the data that is recorded in scale factor=1 in the field to MGA94 (Map Grid Australia).
I used scale factor-only cordinate system in the total station. Now I need to change whole data to MGA datum. I have a MGA grid datum point that I can adopt in my data. When I changed the coordinate system to MGA94 in project property, it seems data is projected to MGA Grid datum but some of the data didn't change such as the keied in points/points that I used for recetion.
Can you please tell me how to solve this in TGO?
thanks
Hello EK,
Perhaps there is a better way to do this, but here is what comes to my mind:
- In your [scale factor=1] job, perform any translations necessary to get your collected point to coincide with it's actual grid coordinate. This is the point you will use to scale your "ground" coordinates to grid.
- Export all points to an ascii file.
- Create a new project in your desired map projection; MGA94, for example.
- Insert a point into this new project using the scaling point identified in the first step. (Your project will still be in your grid system)
- Now you can use TGO to scale to ground coordinates, picking this point (from the map) as the scaling point. TGO will apply the proper combined scale factor for your entered grid coordinate. You are now scaled to ground coordinates, with this origin being the ONLY point that will match exactly with grid.
- Import the ascii file that you created with your total station/ground coordinates. These should import with their identical values, but please check to make sure.
- Now you can tell TGO to un-scale the points to return to grid, and all your ground points should be scaled properly to your project's grid.
This is from memory, as I haven't worked in TGO for years, so please perform your own checks to ensure this procedure yields the proper results.
You can do affine coordinate transformations in TGO to apply translation, rotation and scale.
The function is under the [Survey] pull down menu...select on the 'Coordinate Transformations...' option. From there I recommend clicking on the Point List button.
In this case you will need a minimum of two points with known coordinates in each system to do the transformation. More than two will provide you with an overdetermined solution with residuals to examine...always a good idea. You can apply the transformation to all points in the database or a user selected subset.
The complete details are in the help file. Hit the F1 function key to bring up the help dialog while in TGO then search for Coordinate Transformation under the Index tab.
Note that the coordinates of points with an assigned quality of 'Control' or 'Adjusted' in TGO are not transformed. If necessary, you can edit the quality type in the Point Properties dialog prior to the transformation, then reassign them.
Thanks for your help.
Thanks.
