[mapserver-commits] r10492 - trunk/docs/en/development/rfc

[svn at osgeo.org]

Author: dmorissette
Date: 2010-09-01 20:56:43 +0000 (Wed, 01 Sep 2010)
New Revision: 10492

Modified:
   trunk/docs/en/development/rfc/ms-rfc-60.txt
Log:
Update following discussion. Enabled by default with MAXOVERLAPANGLE == 22.5

Modified: trunk/docs/en/development/rfc/ms-rfc-60.txt
===================================================================
--- trunk/docs/en/development/rfc/ms-rfc-60.txt	2010-09-01 20:56:31 UTC (rev 10491)
+++ trunk/docs/en/development/rfc/ms-rfc-60.txt	2010-09-01 20:56:43 UTC (rev 10492)
@@ -57,7 +57,7 @@
 
 We have found that it is of no use to test the character bboxes for 
 overlap since most of them overlap in normal situations as we can see in 
-the following image:
+the following images:
 
 http://trac.osgeo.org/mapserver/attachment/ticket/3523/mapserver-label-boxes.png
 
@@ -71,7 +71,11 @@
 
 http://trac.osgeo.org/mapserver/attachment/ticket/3523/mapserver-label-with-fix.png
 
+Here is another example with a street map:
 
+http://trac.osgeo.org/mapserver/attachment/ticket/3523/maxoverlapangle-2.png
+
+
 Technical Solution
 ------------------------------------------------------------------------------
 
@@ -79,23 +83,24 @@
 value is the angle threshold to use in filtering out ANGLE FOLLOW labels in 
 which characters overlap (floating point value in degrees). 
 
-NOTE: Better suggestions for the MAXOVERLAPANGLE keyword name are much welcome!
+This filtering will be enabled by default starting with MapServer 6.0. The 
+default MAXOVERLAPANGLE value will be 22.5 degrees, which also matches the
+default in GeoServer. Users will be free to tune the value up or down 
+depending on the type of data they are dealing with and their tolerance 
+to bad overlap in labels.
 
-Setting MAXOVERLAPANGLE in a given LABEL block will
-enable this option and the docs will recommend a default value of 22.5 degrees.
-Users will be free to tune the value up or down depending on the type of data
-they are dealing with and their tolerance to bad overlap in labels.
+Setting MAXOVERLAPANGLE == 0 will completely disable filtering of labels
+based on this criteria, restoring the pre-6.0 behavior.
 
-The default behavior of the software if this parameter is not set will 
-remain unchanged, i.e. this test will be disabled by default and no labels 
-will be skipped.
-
 Usage example
 ------------------------------------------------------------------------------
 
-This example will enable filtering out of ANGLE FOLLOW labels using a 
-threshold of 22.5 degrees of overlap between two consecutive characters:
+This feature is enabled by default with a default value of 22.5 degrees, 
+so no mapfile changes are required to enable it.
 
+This example will increase the MAXOVERLAPANGLE to 30 degrees, resulting in 
+less labels being skipped:
+
 ::
 
   MAP
@@ -103,7 +108,7 @@
     LABEL
        ANGLE FOLLOW
        ...
-       MAXOVERLAPANGLE 22.5
+       MAXOVERLAPANGLE 30
     END
     ...   
   END
@@ -134,9 +139,15 @@
 Backwards Compatibility Issues
 ------------------------------------------------------------------------------
 
-There is no backwards compatibility issues. By default the
-LABEL.MAXOVERLAPANGLE parameter is set to 0, so not applied.
+This new feature will be enabled by default with a default MAXOVERLAPANGLE 
+value of 22.5 degreees. Existing mapfiles will work without any change, but 
+may end up producing maps with less labels if they contain several bad labels 
+with overlapping characters. It is always possible to come back to the old
+behavior (disabling filtering) using MAXOVERLAPANGLE 0 or to tune the value
+up or down to get better results.
 
+There is no other backwards compatibility issue.
+
 Files Impacted
 ------------------------------------------------------------------------------