Spatial Reference of HK

The spatial reference of Hong Kong could be found at : http://spatialreference.org/ref/epsg/2326/

There is a link "Proj4" in that page which provides the Proj4js definitions for converting EPSG:2326 (HK1980 Grid) projection to other projection using the Proj4js library:

+proj=tmerc +lat_0=22.31213333333334 +lon_0=114.1785555555556 +k=1 +x_0=836694.05 +y_0=819069.8 +ellps=intl +towgs84=-162.619,-276.959,-161.764,0.067753,-2.24365,-1.15883,-1.09425 +units=m +no_defs 

Command line to get installed software / windows updates information

One can use wmic command to get the list of product installed in Windows:
 c:\> wmic product

You can also specify which data fields you want to retrieve, e.g.:
 c:\> wmic product get caption

We can also use wmic command to get the list of windows updates made on the machine:
 c:\> wmic qfe list

Solving disk offline issue in Windows

You may experienced a message "The disk is offline because it has a signature collision with another disk that is online" / "磁碟簽章發生衝突" in Windows. The case for myself is switching two RAID-1 drives back to non-RAID devices, where the two drives will become identical and cause the collision problem. The following is the solution to turn on the offline disk:

c:\>diskpart
c:\>list disk (you may see your offline disk is in the list)
c:\>select disk 1
c:\>offline disk
c:\>online disk


Reference: http://beddingmall.blogspot.com/2011/01/blog-post_04.html

Delete Acronis Failed Task

Just tried their solution, it works:

1. Run Schedmgr.exe and issue the following command: task zap
2. Delete the content of the following folders:
   Windows XP, Windows 2000/2003 (32/64 bit)
   - \Documents and Settings\All Users\Application Data\Acronis\BackupAndRecovery\MMS\Policies\
   - \Documents and Settings\All Users\Application Data\Acronis\BackupAndRecovery\MMS\TasksStorage\
   - \Documents and Settings\All Users\Application Data\Acronis\BackupAndRecovery\MMS\PolicyStatistics
   Windows Vista, Windows 7, Windows Server 2008 (32/64 bit)
   - \ProgramData\Acronis\BackupAndRecovery\MMS\Policies\
   - \ProgramData\Acronis\BackupAndRecovery\MMS\TasksStorage\
   - \ProgramData\Acronis\BackupAndRecovery\MMS\PolicyStatistics
3. Recreate the tasks

Ref: http://forum.acronis.com/forum/10652

Column aggregation in Oracle

Suppose we have a table (TBL) in Oracle with columns (CATEGORY, ATTR). Consider the following:

CATEGORY	ATTR
1	A
1	B
1	C
2	D
2	E
2	F
3	X
3	Y
3	Z

We want to convert the table as follows:

CATEGORY	ATTR
1	A,B,C
2	D,E,F
3	X,Y,Z

This can be done via the SQL below:

select CATEGORY, 
       xmlagg(xmlelement(c, ATTR || ',')).extract('//text()') 
from TBL 
group by CATEGORY

Determine user in Tomcat

To determine user authentication info in Tomcat, we can use the following:

getRemoteUser()
isUserInRole(String role)

Both methods are under javax.servlet.http.HttpServletRequest.