Survey coordinate transformation

I started a project at the beginning of the year surveying in UTM and I realize now that it it needs to be in 3TM, I already have UTM and 3TM coordinates for my control points.

I tried grouping my UTM points and shifting them onto my 3TM control points (shifted to one point then stretching/ rotating to a cp on the opposite side of the project) using the standard "move" and "shift" command however when I check to a point in the middle I'm out ~0.2m.

It seems like when I stretch/rotate the opposite control point; the points inside the project don't stretch/rotate with it (I know this because the distance between the UTM and 3TM remain about the same before and after).

I know acad has a very complicated way to to do coordinate transformations for you but there must be an easier way to match one set of control points to another.

Any thoughts?

I am a bit uneasy when you mention the word "stretch".

I would make a block of one set of coordinates, and then use Align to fit to the other set of coordinates. I presume that there is some scaling involved between the two.

I am a bit uneasy when you mention the word "stretch".

 

I would make a block of one set of coordinates, and then use Align to fit to the other set of coordinates. I presume that there is some scaling involved between the two.

I tried the "align" command too and it yielded the same results as the "move" command.

I thought that since I have several control points that I can fit to the stretch command done over several points might yield better results.

It all depends on what accuracy the original control points were. If each set is a geometrical entity, then there should be a uniform way of translating one to the other. However, if the distance of the project is large and involves the curvature of the earth, then you will have spherical distortions to cope with.

In the Civil and Surveying flavours of AutoCAD, there is a process called "Rubber Sheeting" which may be useful to you.

In the end, you may have to fall back on "best fit".

I know acad has a very complicated way to to do coordinate transformations for you but there must be an easier way to match one set of control points to another.

There is also a very simple utility for moving points. If the set you want to move is a point group, even simpler. You may have to dig to find it, but you can move points as easily as you move other objects, just give a displacement.

It all depends on what accuracy the original control points were. If each set is a geometrical entity, then there should be a uniform way of translating one to the other. However, if the distance of the project is large and involves the curvature of the earth, then you will have spherical distortions to cope with.

 

In the Civil and Surveying flavours of AutoCAD, there is a process called "Rubber Sheeting" which may be useful to you.

 

In the end, you may have to fall back on "best fit".

The control points are first order established and maintained by the provincial government. I'll look into rubber sheeting and write back. Thanks for the help.

I wrote an article about Civil 3D coordinate conversions in the October issue of AUGIWorld magazine that might help.