Update Howto.md

Howto.md

-
 # Create a Trigger for a Task #
  
  
-There are different ways to trigger a Task execution process:
+There are different methods to trigger a Task execution process:
 - Using the tag *RunOnTrigger*
-- 
+- Using the tags *SartDate* and *StopDate*
+- Using the filtering tag *FileType*
+
+The most flexible method is actually the *FileType* filter, as everything is treated as a file being processed
+ 
+ 
+ 
+## Using *FileType* filter method
+ 
+ 
+The presence of a dedicated trigger file (eg. TR$PROCESSOR.*.trigger) , or also any other file, filtered by the <FileType> expression,
+acts as a driver for the Task execution. This allows than to create a list of trigger files that the DES can then elaborate in a FIFO queue.
+
+Because the Date for example is often used as input parameter for a processing time series for example,
+the Date has to be passed as input parameter to the Task executing a particular job.
+
+One approach to implement this, is to ensure that the trigger file TR$PROCESSOR.*.trigger includes the date at a certain position, i.e position 5 (. separated):
+```
+TREURAC_RADBEAM_P.southtyrol_highres.6120_6120.hour.8.2017-02-10T15:00:00.Eurac.01.00.trigger
+```
+
+So the implemented wrapper Script (Perl, Python, Shell) or Java Class for the Task can extract the processing parameters as needed, i.e. The date to be processed. 
+The trigger file itself might contain even a more structured meta information in form of XML for example.
+
+By convention the trigger file should have the following naming convention:
+```
+TR$PROCESSOR.$AOI.TileID.Type.Value.Date.Eurac.$versionMajor.$versionMinor.trigger
+```
+Any other naming convention can be adapted by providing an appropriate wrapper script that is called.
 
+### Example ###
 
+**Processor configuration:**
+```xml
+<TaskGroup name="Processing" type="serial" active="yes" priority="NORM">
+	<Task name="createMap" type="cmd" active="yes" priority="NORM">
+		<EMail>mail@host.yourdomain</EMail>
+		<NotifyEmail>OnError</NotifyEmail>
+		<FileType>TREURAC_RADBEAM_P.*.trigger</FileType>
+		<Command>sh</Command>
+		<Parameter>/Algorithms/runProc.sh</Parameter>
+	</Task>
+	<Task>
+		...
+	</Task>
+</TaskGroup>
+```
+ 
+ 
+**Task implementation:** (*runProc.sh*)
+```sh
+#!/bin/sh
+arg=($*)
+BASE_PATH=$1
+AOI_NAME=$2
+PROCESSOR_NAME=$3
+TRIGGER_FILE_NAME=$4
+ 
+echo "creating environment vars.."
+# User specific aliases and functions
+export PATH=$PATH:/raid0/Algorithms/...
+ 
+echo "start processing..."
+ 
+file=$TRIGGER_FILE_NAME
+echo "  processing file: $file"
+ 
+DATE_FROM_FILE=$(echo "$file" | cut -d '.' -f 6)
+echo "date: $DATE_FROM_FILE"
+ 
+DATE=`date -d "$DATE_FROM_FILE"  +"%Y-%m-%d"`
+HOUR=`date -d "$DATE_FROM_FILE" +"%H"`
+HOUR2=$HOUR
+HOUR=`expr $HOUR2 + 1`
+MIN=`date -d "$DATE_FROM_FILE" +"%M"`
+ 
+echo "running algorithm for date: $DATE"
+```
+ 
+