[Mapserver-users] "SUM: DHTML Navigation Tools for MapScript"

[Steve Lime]

I'll talk to the UMN folks about a new repository soon, although nothing
is likely to happen until after the holidays.

One thing I'd like to bring up is that I'd like to see applets and DHTML
to both be considered here. Contrary to public opinion I don't think
applets are dead, nor is the technology that drives things like jbox or
rosa (LiveConnect). When LiveConnect support becomes widespread again
(IE supports it and that 90% of the market) I for one would like to roll
out dhmtl or java versions. It may be that long term applets hold more
promise. I'd really like to see a common API that would allow you to
access events in either java or dhtml. Things like coordinate, layer,
legend, and reference map mangagement being totally seperate (i.e.
non-graphical stuff), implemented in javascript but not dependent on
what the user interface is written in. This would allow for even more
user interfaces (like flash or svg!) to leverage the same code. The
dhtml/java/flash/svg code could then be *very* simple and would only
need adhere to a relatively simple api for reporting events (e.g.
box/mouse coordinates).

The backend javascript that communitates with whatever would use the
event information from the ui to construct URLs to use to retrieve
components (maps, scalebars, legends, reference maps) and make them
available to the page. I would suggest using the base MapServer CGI
syntax (which already handles some ROSA nuances) as the communication
API with oportunities to extent it of course.

Before a bunch of coding takes place, it would seem to be to make sense
for folks with existing code to inventory and document what they have.
Then we can pick and choose from that lot and move forward. This would
include the ROSA and jbox (formerly mapplet) tools.

Steve

Stephen Lime
Data & Applications Manager

Minnesota DNR
500 Lafayette Road
St. Paul, MN 55155
651-297-2937
>>> "Hankley, Chip" <Chip.Hankley at GASAI.com> 12/19/02 15:34 PM >>>
I've received a LOT of responses since I posted this question... some
off-line, so I thought it might be a good time to SUM. There are about
five
or six folks who were interested in contributing to development.

Apparently a lot of us have been working on DHTML navigation tools...
there
are already some fairly refined tools - so there is probably not a need
to
re-invent this. Martin Weinelt's and Steve Lime's provide a good
foundation... so we could probably start with their work, and make some
modifications to build a modular 'plug-in' that could be used with
MapServer
or MapScript.

A number of people suggested a 'skin' type approach... the idea being to
create a more comprehensive application where all you have to do is
supply a
link to a mapfile and it works. While I think these types of apps are
great
and worthy of development, it's not really what I'm interested in here.
The
best explanation that I can come up with is that I want to develop a
DHTML
version of ROSA.  Such a tool could certainly be used as PART of a
Skin-type
application, but could be used independently in MapScript (or MapServer)
apps when developers want to create something that is more customized.

I'll try to explain a little better what MY goals for a DHTML navigation
toolset are:

FUNCTIONS
-------------------------
o Click & drag boxes.
  
  User clicks and drags a box on the image. The tool returns 
  the bounding coordinates of the box (in image coordinates).

o Single point click.

  User clicks on the image. The tool returns the coordinates of
  click (in image coordinates).

o Image drag (for panning)

o Mouse move capture (image coordinates) in order to display 
  geo coordinates.

o 'Custom' button.

  When the user clicks the button, some JS code is executed.

o 'Measure' tool.

  User clicks on the image and either:
    a) clicks a second time to identify the 'end' of the 
       measure segment
    b) is allowed to continue 'clicking' to simulate 
       vertices of a measured line segment, with a double
       -click identifying the end of the measure segment.

  Values returned are in image coordinates.

DESIGN PARAMETERS
----------------------------
o A 'tool' will always be associated with an image that functions as a
button.
o A 'tool' will have image swaps for the 'over' and 'click' events
o Implementing a tool should be as simple as possible from the main
program
interface... something like this

  <new tool> = createTool(<new tool>, <offImage>, <overImage>,
<onImage>, 
               <action type>, <form name>, <form field>, <coord field>);

  example:
  navZoomIn = createTool('navZoomIn', 'ZoomInOff.png', 'ZoomInOver.png',
'ZoomInOn.png',
              'rectangle', 'frmMap', 'CMD', 'COORDS');

  When the user uses this tool, a field called 'CMD' in the form
'frmMap'
will be given 
  the value of 'navZoomIn'. The image coordinates of the drag event will
be
placed in 
  the filed 'COORDS'.

  The goal here is to provide kind of a navigation API... so that users
can
implement the 
  tools without really having to know what's going on in the background.
They would simply 
  have to make sure that their main program included the references to
the
JS files.

o At a minimum, should work in IE 5+, Mozilla 1.01+, or NS 7+. Would be
nice
if it worked with other browsers
  (Konqueror, Opera, AOL?).

----------------------------

As I mentioned in my previous post, I have no experience developing
something in a 'team' environment like that... so I have no idea where
to
begin. Someone suggested setting up a CVS and mailing list... for those
of
you that have done other development, would this project be suitable for
something like that, is it overkill? Do I have to set up my own CVS, or
could we use one of the environments that is already set up for
MapServer
development?

Thanks!

Chip
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