Occurrence:
I need to view both my local mine grid data and real earth data in the one mapper window. Traditionally many people use a simple Non-Earth (metres) coordinate system to display local mine gridded data, or data from a sampling grid in a project area.
Creating a custom affine projection will allow the local mine data to be directly compatible with any real world coordinate system.
Solution:
The control point table for a custom affine projection transformation must contain four columns which read
from left to right as UTM_Easting, UTM_Northing, Local_Easting and Local_Northing. The naming convention
of the column headings is not important, but the order of the columns is critical. An example of a control
point table can be seen below.
To Transform non-earth coordinates to a standard projection and also generate a custom projection system for the non-earth coordinates -
1. Open the table to transform into MapInfo. The transformation target table must be mappable and in a stnadard projection, e.g. UTM or MGA. If no data is available, you may also use the Control Point table for the transformation target table, by simply Creating Points for the UTM (MGA) coordinates.
2. In the Discover>Data Utilities>Transform Coordinates dialog, select the table to transform from the Transformation Target Table list.
Choose Affine from the Transformation Type pull-down list.
3. Set the Transformation Target for Map Objects.
4. Click on the Control Point Table button and browse to the control point table. The selected control point
table will be displayed on the Control Point Button. This table does not need to be mappable.
5. Check the Calculate Parameters only, Show Transform Parameters and Make Affine Coordsys box and click OK.
6. Select the required standard projection for the UTM (MGA) coordinate fields from the Choose
Projection dialog (this will be the base projection for which the custom affine is based on).
7. Discover will create the affine transformation and add the custom coordinate system description to the MAPTRAN.LOG file. An example Maptran.log can be seen below.
NOTE: If you have a _trans table created, this will be incorrect. You will need to delete this an recreate your local grid points in the new custom projection.
7. Copy the line beginning “My affine coordinate system” from the MAPTRAN.LOG file
and paste into the bottom of your MAPINFOW.PRJ file. The MAPINFOW.PRJ file is located in the
..\\MapInfo\Professional directory.
8. Assign a new name for the custom projection and add a new projection Category line above if desired.
This projection category can be used to keep all your custom projections together, and should be in the
format below:
"--- Custom Projections ---"
9. Add an appropriate bounds clause to the projection line. The bounds clause is used to specify coordinate
limits. To specify bounds for the new projection enter the appropriate min_x, min_y, max_x, max_y values
for your data as per the example below. Replace the min_x, min_y, max_x, max_y entries with appropriate
values for your data. In the following example bounds of -10000000, -10000000, 10000000, 10000000 have been
used.
Alternatively, simply change the first 3008 code to 1008.
Example of a custom projection in the MAPINFOW.PRJ file:
"--- Custom Coordinate Systems ---"
"Sylvania Local Grid", 3008, 13,7, 141, 0, 0.9996, 500000, 10000000, 7, 0.895898, -0.444543, 3108129.02, 0.444537, 0.895887, -6726798.31, -10000000, -10000000, 10000000, 10000000
For any existing maps in local non-earth, you will need to recreate the points in the new custom projection.
For any existing maps in UTM (MGA), you can convert these into the local grid by simply re-projecting and selecting the custom projection.
