MapInfo Products KnowledgeBase

Product: MapInfo Professional
Version: 10.x, 9.x
Platform: Not Platform Related
Category: Object Editing

Summary:
*Object thinning.

Question:
How to perform object thinning.

Answer:
What is object thinning and why would it be used?

Object thinning is the automatic removal of nodes in polygons based on how close they are together or how co-linear they are. This makes it possible to simplify complex geographical data so that MapInfo Professional can manipulate it more quickly. This functionality is geared more towards ‘power users’ who work with large sets of data. Highly detailed spatial data sets from such applications as Oracle Spatial, AutoCad or MicroStation Design can be imported into MapInfo Professional and then thinned for ease of use and faster rendering times in the MapXtreme line of products.




1. Open the Workspace called ‘Node_Thinning’. This workspace represents a sample of high resolution UK Postcode Sectors thematically shaded by their corresponding Admin areas.

2. Before thinning a table, the layer in the map must be made editable. Choose Map>Layer Control. Place a check in the pencil column for the layer to be thinned:



Turning the display of nodes on or off for a particular layer in a map can be accomplished by clicking on the display button and putting a check in the Show Nodes check box (This display option does not have to be on for the Thinning process to work. It is merely for display purposes only):



3. Click OK on the Display Options dialog, and then OK again on the Layer Control dialog.
4. Next, select the objects to be thinned. This can be accomplished by using the select tools located in the Main tool bar or SQL Select. In this example, select all the objects using Query>Select.

5. Choose Query>Select. In the Select dialog, select records from table Postcode_Sector, and un-check the Browse Results option. Click OK:



6. Now that the objects are selected, start the thinning process. Choose Objects>Snap/Thin. Place a check in the Enable Node Thinning/Generalization check box. Set the Distance Units to be Meters. Enter a value of 100 meters for both 3-Node Collinear Deviation and Node Separation (For more information regarding the 3-Node Collinear Deviation and Node Separation settings, click the Help button or see the Q and A section at the end of this document):



7. Click OK. If the resulting operation does not produce the desired results, undo or revert the changes to the table by choosing File>Revert Table.

Before Thinning:



After Thinning:



Q AND A:

If the 3-node Collinear Deviation number is increased, what is increasing?

The minimum triangle height required for the Thinning operation to leave a given 3-node triangle alone (not remove any nodes).

In other words -- take three consecutive nodes in a polyline or region, and draw a triangle with them:



The blue line represents a section of the region or polyline to be thinned. If the height of the triangle (green line) is shorter than the 3-node Collinear Deviation setting (100 meters, in this case) then node 2 will be thinned out (removed), thus turning the triangle into a straight line. If the green line is longer than 100 meters, node 2 won't be removed -- the triangle is judged to be "significant", so it is left alone.

Last Modified: 04/20/2010 03:33:45 PM
Document URL: http://testdrive.mapinfo.com/techsupp/miprod.nsf/kbase_by_product/C04149D2C49B7AE185256AAB006E0349

*Object thinning.^C04149D2C49B7AE185256AAB006E0349^Y