Technical Details of the Geophile Demo

• The data set
  • The data set contains 20,000 boxes in a space of resolution 450 x 450.
  • Box width and height are normally distributed with a mean of 4 and a standard deviation of 4.
  • Box positions are uniformly distributed.
  • Box colors use an RGB color scheme. Each component is uniformly distributed in the range 0-255.
  • The image representing the data set is a static GIF file, (i.e. it is not generated each time the demo page is loaded).
• The database
  • Each box is a distinct object.
  • The data set is stored in a sorted flat file.
  • The data structure underlying the Geophile index abstraction is an array, implemented on top of the flat file. Random access is implemented using binary search, and sequential access simply increments or decrements a subscript.
• The query
  • The query position is selected by the user by clicking on the image representing the data set.
  • Query size is 10 x 10, centered around the position selected by the user.
  • The query is evaluated by creating a second Geophile index and carrying out a spatial join with the data set.
• Result processing
  • The boxes resulting from the spatial join are drawn to a PNG file which is returned to the user.
  • Query results are sorted to preserve the drawing order of the original data set.
  • The query region is magnified to 450 x 450.