Programmers Documentation for Stream Mode Digitizing Extension for ArcView

OVERVIEW
This extension contains a Form that allows the user to digitize graphics or
shapes on-screen using a "Stream" mode rather than a "Click" mode. Stream mode
means that coordinates are recorded based on the location of the mouse without
having to specify vertices by clicking on the mouse. Just move the mouse on the
View document and the coordinates are recorded.

Stream mode digitizing is for PolyLines and Polygons only. There is no function
to support Stream capture of Point features.

Using the tools on this form you can:

1) Capture Lines
2) Capture Polygons
3) Split Polygons or Lines
4) Append to Existing Polygons

HOW TO USE THE TOOLS.

When you load the extension you will see a new button added to the View Document 
Interface with a squiggly line as the icon. This button opens the Stream Mode Digitizing
Form. This form has a couple of inputs and 5 tools. Each tool is used to add or modify
shapes on a view document. To digitize simply press the tool of interest, then press
and hold the SHIFT key on the keyboard. To start a shape move the mouse over the View and
press and release the Left Mouse button. As you move the mouse around the view, the line
you are capturing is displayed. To stop digitizing simply release the SHIFT key. At this
point the line will be Smoothed and Generalized if the options are checked, and then
added to the View.

If a theme is editable the shape will be added to that theme. If no themes are editable
then the shape will be added as a graphic to the View.

TOLERANCES

There are two tolerances that you need to be aware of when using this extension:

Smoothing Level - This option, when checked, causes lines added by the user
to be smoothed using an Iterative Bezier Curve algorithm. Use the Slider bar to define
the amount of smoothing you want to occurr. More smoothing causing corners loose their 
definition, less smoothing causes the line to be more like the original but smoother.

Distance Tolerance - This tolerance is used when actually capturing points. Any 
new point that is closer to the previous point than this tolerance is not captured.
This tolerance is used to prevent a horribly dense line.

The default value is calculated as 1/10,000 of the View extent. You can change the
tolerance by typing in a value or by interactively defining a circle on the view using
the Interactive Distance Tolerance tool.

HOW IT ALL WORKS.

As you add a line or polygon the coordinates of the current mouse location are recorded 
every 0.1 seconds. Each point is compared with the previous point to see if it outside the
distance tolerance. If it is then it is added as a line segment. Once you release the mouse,
if the Smooth Lines option is selected, the line will then be smoothed. During
this process, lot's of vertices will be added to the line to facilitate the smoothing.

Then, if the Generalize Lines option is selected, the new line will be generalized using 
the Distance Tolerance value, ensuring that no two vertices in the line are closer than this
value. 

It has been my experience that if you smooth lines you should also generalize them to 
remove the un-needed vertices. You need to experiment with these values to find what works
best for your particular application.

SNAPPING
There are no snapping options in this tool-set. All snapping defined by the Theme's properties
are applied. Consult the ArcView documentation on snapping to learn more....

NOTE:
This is a beta release of the product. If you find any problems with it please contact
Tim Loesch at tim.loesch@dnr.state.mn.us or via phone at (651) 296-0654.