Vector data simply can not "come apart" if you merge subprojects formed by the Create Subprojects utility - every subprojects gets to its place for sure. But it is not always true for projects created separately..

Import in Easy Trace is possible only into an existing project which has vector field compatible with the data you want to import. Actually, project vector field can be automatically increased at import not more than tenfold in any of the four directions.

This limitation is caused by the form of coordinate storing in Easy Trace - as fixed-point values. Till recently, it gave significant saving of time at data processing on PC...

If coordinates of vector data you want to import are outside the limits of possible values, they can not be converted into inner Easy Trace coordinates. Import will be canceled and you will see an error message.

But sometimes data can be imported into one project but don't join each other. It is connected with wrong coordinates specified for one (or both) subprojects.

To correct the error, import should be repeated with coordinate transformation. The Transform page of the Import Wizard enables this operation.

The affine coordinate transformation is provided in Easy Trace now. It is based on a set of reference points. Such a set can be taken:

• from the Easy Trace layer containing reference points;
• from an external CPT-file;
• from a TAB-file of raster registration in MapInfo;
• from a MAP-file of raster registration in OziExplorer.

Layer of reference points

- is an ordinary vector layer; its point objects are linked to a database table having the fields of the Float or Numeric type called _X_CPT_ and _Y_CPT_ (the layer must belong to the TARGET PROJECT).

Example: One sheet of the map is displaced after import.

1. Write down coordinates of four corners of the sheet we want to import;
2. Create a new layer in the target project. Create a database table for this layer. The table must contain the "_X_CPT_" and "_Y_CPT_" fields of the Float or Numeric type;
3. Input 4 points to this layer where corners of the sheet you want to import should be. Perhaps, you will have to increase the project field first, see Project->Properties->Project Frame;



4. Fill the database table for the points - input coordinates (item 1) to the"_X_CPT_" and "_Y_CPT_" fields;
5. Select the "Transform coordinates using control points from the layer" option on the Transform page at import and specify the layer.

File of reference points

A *.cpt- file is a text file in which one string corresponds to each control point. This string contains 4 coordinate values separated by spaces:

• the first pair corresponds to the control point's coordinates in the current project.
• the second pair corresponds to its coordinates in the project to be imported (or target system at export).

There should be 3 reference points at the least in the set that don't belong to the same straight line. If the set contains more than 3 points, the program calculates the affine transformation applying the least-squares method for all the points. Thus, "superfluous" points are used for error averaging.

In detail :

1. Select three reference points in the project WHERE TO you are going to import data. It is convenient (but not necessary) to use frame corners as reference points. Measure coordinates of these points: P1(x1,y1), P2(x2,y2) ,P3(x3,y3).

2. Measure coordinates of the same points in the external "incorrect" project. It is convenient to input point objects at these places - you will see their coordinates in a pop-up window after selection with the Editor. Or you may simply navigate the cursor to these points in turn and read the coordinates in the lower left corner of the screen. So, these coordinates are (u1,v1), (u2,v2), (u3,v3).

3. Make a file of reference points containing the following three strings:

4. If one subproject at least has correct coordinates, export all the others into it. If all subprojects are bad, create a new project having correct coordinates and covering the entire are of all subprojects.

5. At import, specify the created file of control points in the Transform page.

DO NOT CONFUSE THE ORDER of coordinates in the file - coordinates of the point in the current project should be specified first, and in the project to be imported - after it. To make sure, select the file and click the Control points button to open the Control Point Statistics dialog box. In the table you will see the order of coordinate list.

Two more notes in the end: