VISTA FAQ

FAQ: (version 0.1) 07/27/98

Q.I-1. What is VISTA?
Q.I-2. How do I get my hands on a working copy?
Q.I-3. What do I need to use VISTA?
Q.I-4. Why is VISTA in Java?
Q.I-5. VISTA is client/server application. What does that mean?

Q.II-1. What kind of data are we talking about? 
Q.II-2. How is this data stored?
Q.II-3. What is pathname?
Q.II-4. What is Data Reference?
Q.II-5. What is a Group?
Q.II-6. What is a Session? 

Q.III-1. How do I get started?
Q.III-2. How do I open connection to a remote or local server?
Q.III-3. How can I look at data from different files at the same time?
Q.III-4. How can I look at data in different places on the Internet?
Q.III-5. I have a lot of data? Can I filter out to see only some?
Q.III-6. I have lots of similar data? Can I merge them? 
Q.III-7. I have data with different time intervals? Can I period
average?
Q.III-8. I want to write the data out to a local file? How can I do
that?
Q.III-9. How do I add/subtract two timeseries or do other math
operations? 

Q.IV-1. What is scripting?
Q.IV-2. Where can I get some samples on scripting?

A.I-1

VISTA stands for VISualization Tool and Analyzer. It is a tool for
data retrieval, management, manipulation and visualization. 

Currently VISTA can retrieve data from a local or remote data base
file. It manages the data as sessions, groups and data references (
All these concepts are explained in section II). It allows for
mathematical manipulations as well as period averaging, moving
average, etcetra. Visualization is in the form of 2D graphs which are
scatter or time-series plots.

A.I-2
	Check out http://wwwdelmod.water.ca.gov. Follow the links for
VISTA. Download it and follow the instructions.

A.I-3

VISTA is almost entirely written in Java ( except for DSS database
access ). This means that it almost works on Win NT/Solaris. If you
are only concerned with viewing data then VISTA should work from any
platform that supports a Java VM. For more details check out
java.sun.com 

VISTA is written with object-oriented concepts and has modules that
carry out particular operations. Some documentation is available from
a automatic generation tool. I will also be working on a developer's
manual. 

A.I-5

VISTA is written in Java for portability, network awareness and ease
of writing programs.


A.II-1.
	We are primarily talking about time-series data and paired
data. In generality a (x,y) pair is one element of this data where x
is usually time and y the value.

A.II-2. 
	This data is stored in a database developed by HEC called
HEC-DSS. It is NOT a relational database and is specifically tuned for
fast storage and retrieval of time-series data sets. For more
information visit HEC at http://wrc-hec.usace.army.mil/

A.II-3. 
	HEC-DSS stores data sets referenced by pathnames. Each unique
pathname within a file refers to a unique data set. A pathname
consists of A through F parts. A and F part are descriptive parameters
for the data set, B is the location name of the data, C is the type of
data, D is the time window and E is the time interval.

A.II-4.
	A data reference is a reference to a data set. It contains
information such as the filename, the pathname, the timewindow (if
any), the time interval (if any). A data reference can be either
actual data on the disk or could refer to virtual data ( data that has
resulted from a series of operations ).

A.II-5. 
	A Group is a group of data references. A DSS file may be
thought of as a default group that contains all the pathnames in that
DSS file

A.II-6.
	A Session is a group of Groups. It can be thought of as a
directory of DSS files. However the analogy is limited as a Session
could consist of Groups consisting of data from different web
addresses, different files and even Groups containing virtual data
sets. 

A.III-1.
	To get started you need to have VISTA installed correctly. If
you did everything correctly a frame should come up. 
	Additionally you need data that you can look at. If you have
local data you can look at it. 
	To get started follow these steps:
a.) Click on Session|Open|Connection menu. This should bring up a
dialog box with server and directory text fields. Enter the word
"local" for the server and the full directory address of the directory
in which the data. ( note: It is important to enter the DIRECTORY and
NOT the filename) . Click OK.
	If you entered incorrectly a dialog box with the error message
will pop up. Click OK on those dialog boxes and try step (a) again

b.) If no more dialog boxes pop up then a listing of all dss files (
files ending in .dss ) should show up in the frame. Select one of
those dss files by clicking on it.

c.) Click on Group|Open menu. This should bring up a new window ( a
group window ) which displays the pathnames available in the dss file.

d.) Click on a pathname to select it. In this Group display window
click on Data|Show As...|Table to display the data in tabular
format. You can alternatively click on Data|Show As...|Graph to get a
graph of the same data.

e.) If you reached this step, you are done for now. There are many
more things to discover in VISTA. I will be adding more answers
depending upon the feedback I get from you.

A.III-2.
	To open a remote server you must know its internet address (
similar to how you know a web address ) or the server machine's IP
address ( address with numbers that no one remembers )
	To open a local server you may use the key word "local".
	Now when you click on Session|Open|Connection menu item, a
dialog box will pop up. You can enter the name of the server machine
or the word "local" and the directory where dss files reside. And then
click OK.

A.III-3.
	To look at data in different files at the same time you must
first open a connection to those files. Then select all the files that
you must view together ( using a mouse drag or ctrl key + mouse for
intermittent selection ).
	Once all the files are selected, click on Group|Union menu
item. This will add a new group to the current session which will be a
union of all those selected. Then open the group as usual. You should
see the data from all the files in the same group.

A.III-4.	
	The answer is : See A.III-3. You can keep opening connections
to as many server/directory combinations as you like. Each connection
will add the dss files available on that machine and directory to your
current session.

A.III-5.
	Open the Group (DSS file ). Then look at the panel that has
the word filter. The filter panel allows you to reject or select
pathnames based on regular expressions for each pathname part or the
entire pathname.
	Regular expressions are extremely powerful way of specifying
strings however to get started you may enter words like 'stt' in one
of the pathname parts field. On pressing the return key all pathnames
whose that part have the letters stt in them would be selected.

A.III-6.
	Sometimes a location may have data that is similar in all
respects except that it belongs to two different time-periods. This
means the data is represented by two different pathnames. That is
where the merge operation comes in handy.
	Select the data that needs to be merged. Then choose the
"Period Ops" tab from the Math Panel. Click on "Merge References"
button. That should create a new data reference that is added to end
of this group. It has in its B part the word "merged". This merged
data though virtual can now be considered just as another data set.

A III-7.
	Again select the data you want period averaged. Then choose
the "Period Ops" tab from the Math Panel. Choose the interval from the
drop down combo box and the type of period operation ( in this case
period average) Then click on the "DO OPERATION" button. This should
add a new data reference to the group having the "PER-AVG" appended to
the B part of the original data reference

A III-8.
	Select the data you want saved to a dss file. Then choose from
the menu Data|Export Data To...|DSS. Enter the name of the file and it
location in the file dialog and press OK. This will save the pathname
to the desired filename.

A III-9.
	To do math operations click on the "Math" tab in the Math
panel. 
	Lets try to subtract two data references. Select the first
data reference. Then click the button corresponding to the operation (
in this case "-" ). Then click on the second data reference. The click
on the button "=". This should add a new data reference to the group
with the B part set to : (B part of 1st  - B part of 2nd) and F part
set to MATH_COMP.
	
	Lets now try to add a number to a data reference. First select
the data reference by click on it. Then make sure the "Use Number"
checkbox is checked. Then click on the "+" button. Then enter a number
in the field next to the check box. Then click on the "=" button. This
should add a new data reference to the group with B part set to : ( B
part of 1st + number ) and F part set to MATH_COMP