Transector Prototype

Plain Language Code Description

First, a little description about the concept as I see it:

A number of randomly placed and directed transects are placed in a set of polygons, based on user specified transect density and transect length.

The random transect placement is executed by:

• Specifying the set of polygons to be filled with transects.
• Determining the map units for the View's projection (if this is undefined, the user must supply this information.
• Specifying the density as length of transect per area of polygon
• Specifying the length of each individual transect

At this point, the script automatically places the transects:

• For each polygon in the set of bounding polygons
• The correct number of transects for this polygon is determined
• The bounding rectangle of the polygon is found
  • For this polygon, for the number of specified transects
    • A random point is selected within the bounding rectangle
    • A check is made to see if the random point is in the poygon
      • If the point is in the polygon, a random direction is selected and the transect is recorded in the transects theme
      • If the point is not in the polygon, the script selects another and tries again (back up 3 lines)
• Once all polygons have the specified number of transects, the script is done.

Illustrated Sample Run

Here's an illustrated view of how this works. There are about 1.5 megabytes of images here, so please be patient:

Here's a sample set of bounding polygons (bounded in bright green), overlaid on the Glyndon airphoto moasic:

The user activates the script, using a button on the interface (currently marked with a T). A menu item could also be used.
The script inquires which of the polygon themes loaded into the view is the theme that defines the regions:

The script then inquires about the desired transect density (of length per area). Currently this is being requested in metres/hectare, but could easily be another unit:

The script then inquires about the desired length per transect. Since it is unlikely that the ideal number of transects for a given polygon will be a whole number, the number per polygon is currently rounded up (although it can be rounded down or dealt with a variety of other possible fashions):

With all the user specified parameters now entered, the script calculates and places the transects.
Here's a view of all the transects (shown in bright pink) placed over the sample bounding regions overlaid on the Glyndon airphoto mosaic:

Here's the same transects overlaid on the lower resolution digital orthophoto:

Here's a closeup view of one transect overlaid on the Glyndon airphoto mosaic:

Here's the same transect (100 metres long) overlaid on the low resolution digital orthophoto, which is really uninterpretable this close in:

That's about it for now. I'll be getting started on the classifier tool shortly.

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David Tenenbaum davidten@email.unc.edu