Geoinformatica

0.9

Introduction

Geoinformatica is a geospatial software toolkit, which builds on Perl, GTK+, GDAL, and libral. These pages document the Perl modules specific to Geoinformatica.

The source code for these modules and libral are developed at OSGeo Trac. There are nightly snapshots available at http://map.hut.fi/files/Geoinformatica/. In the same ftp site there are Windows binaries available.

Geo::Raster and Geo::Vector contain Perl interfaces and access to computational methods for geospatial data that are mainly in GEOS and libral. In the Gtk2::Ex::Geo namespace there are respective visual classes. The Gtk2::Ex::Geo contains also a set of widgets, dialogs, and glue code for managing a stack of geospatial data layers.

The Geo::OGC::Geometry is (or is intended as) a place for Perl-space geometry data storage and computational code.

The IPC::Gnuplot implements a simple pipe to a gnuplot program which can be linked to Gtk2::Ex::Geo::Glue for plotting.

Geo::Raster

A Geo::Raster object is either a temporary cache of one band of a GDAL raster dataset or an in-memory libral raster. In this documentation Geo::Raster objects are referred to simply as rasters. Technically a raster is a blessed reference to an anonymous hash. Generally, the user should treat the hash values as read-only or not access them at all and instead use the methods. Rasters are either integer or real valued. The Geo::Raster class provides many basic operators and functions for raster computations.

Note:

The raster operations and methods almost always make sense only if the raster is an in-memory libral raster. Technically GDAL rasters are libral rasters too, but the libral raster is only a snapshot created for display. To convert a GDAL raster to a libral raster in the GUI use the clip menu command and dialog.

Many Geo::Raster methods can be used in-place or to return a value. For example:

$a->sin(); 

takes sin of all cell values of $a, while

$b = $a->sin();

creates a new raster and assigns the sin values to it.

A raster is a rectangular matrix of cells. A cell is referred to by its coordinates, i.e., a list ($row, $column) or ($i, $j). For example:

@cell = (30, 40);
$value = $a->get(@cell);

Note:

Usually, if operations involve more than one raster, then the rasters need to be overlayable, i.e., their sizes and world coordinates must match.

The world coordinates of a raster are simple linear transformations from the (row, column) cell coordinates. x has the value min_x on the left edge of the leftmost column and each cell is cell_size wide. y has the value min_y on the bottom edge of the lowest row and the height of each cell is cell_size.

Note:

For maintenance the Geo::Raster class is split into several files. These files appear as subclasses of Geo::Raster in this documentation, but technically there are only classes Geo::Raster and Geo::Raster::Layer.

Geo::Vector

A Geo::Vector object (a blessed reference to an anonymous hash) is a either an extra layer on top of an OGR layer or an array of OGR features.

Introduction to Gtk2::Ex::Geo modules

The Gtk2::Ex::Geo modules provide a plaform for developing geospatial applications.

The Gtk2::Ex::Geo::Layer is an abstract base class for geospatial data layers, it itself is a subclass of Geo::Layer. There are also classes Gtk2::Ex::Geo::Raster and Gtk2::Ex::Geo::Vector, which derive also from Geo::Raster and Geo::Vector.

The Gtk2::Ex::Geo::Overlay is a widget class derived from Gtk2::ScrolledWindow. Gtk2::Ex::Geo::Overlay objects maintain a list of geospatial data layers. The Gtk2::Ex::Geo::Overlay class contains a method for rendering the data onto a geocanvas that is first a cairo surface and then a gdk pixbuf. It also contains methods for user interaction with the widget: zoom, pan, select.

The Gtk2::Ex::Geo::Glue is for maintaining a set of objects: Gtk2::Ex::Geo::Overlay, Gtk2::TreeView, Gtk2::Entry, Gtk2::Toolbar, and Gtk2::Statusbar and linking them. Gtk2::Ex::Geo::Glue can be used to maintain a link to a gnuplot instance.

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