Introduction to Geographic Information Systems in Forest Resources
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Data Export

Discussion:

All GIS software should contain routines for exporting data. For some GIS software, such as ArcInfo, which has a strong position as a data development application, data export routines have been an early and important component.

Other software products designed originally for query and display, such as ArcView, generally have limited export capabilities. These products have historically been more interested in getting data in than getting data out.

Nevertheless, there are a few options for exporting data from ArcView.

  1. Converting feature themes to shapefiles
  2. Converting selected features of a theme to a shapefile
  3. Converting image themes to grids
  4. Exporting grid themes to generic raster format
  5. Exporting feature themes to ArcInfo generate format
  6. Exporting tables
  7. "Exporting" views and layouts
  8. Exporting 3D scenes as VRML

 

Converting feature themes to shapefiles

Feature themes can be "exported" to shapefiles. This means that an ArcInfo coverage, CAD drawing, an event theme, or even another shapefile, can be converted to a shapefile. Any supported vector data set (i.e., anything that appears in a view as points, lines, or polygons) can be converted to the shapefile format. Supported data sets are described in Getting Data into ArcView.

Converting other data sources to shapefiles can be handy when you need to create a feature data source to be moved across a file system or from one machine to another. If you have a shapefile, you can copy the component files across file systems or computers.

Contrast this to the ArcInfo data structure, in which a single feature theme source consists of data files spread across more than one directory, and it is impossible to manage the coverage without ArcInfo.

When a new shapefile is created from an existing theme, ArcView will ask if you want to add this new shapefile as a theme to the current view. If you do not add the theme to the view, the shapefile will still exist on the disk, and can be used later.

Here, the original stands theme is an ArcInfo coverage data set.

It is converted to a shape file.

You can see that there are now two themes representing stands; one is from a coverage data source, and the other is from a shapefile data source.

 

Converting selected features of a theme to a shapefile

Sometimes, you may wish to display only a subset of features of a given theme. One way to accomplish this is to apply a filter to the theme, so that only select features display. Another method is to create a new shape file based on a selection of features. When a set of (one or more) features is selected, and the theme is converted to a shapefile, only the selected set is written to the new shapefile.

Here, only the > 100 year old stands from the stands.shp shapefile are converted to a shapefile of their own:

 

The selected stands are highlighted in yellow.

 

This selected set is converted to a shapefile:

 

Note: if you want to create a shapefile consisting of all the features of a theme, make sure you have no active selection on the theme. Otherwise your new theme will consist of only selected features!

 

Converting image themes to grids

Supported raster data sets, including images, can be converted to grid data sets. The output grids will have cell values identical to the pixel values in the input image. Multi-band images can be converted to grids, one output grid per input image band.

We will cover exporting grids later in the course. See the exercise on Remote Sensing for an example of converting a 7-band LandSat TM image to a series of 7 grids. Converting single-band images is performed in the same manner, except that only a single output grid is created.

 

Exporting grid themes to generic raster format

A selected grid theme can be converted to a generic raster file by using the File > Export Data Source menu choice. This allows a grid theme to be converted to a generic raster format.

The two supported output raster formats are ASCII and binary (IEEE format).

The generic ASCII raster file is a single file composed of 6 lines of header (descriptive and georeferencing) data, followed by lattice mesh point (grid cell) values.

The generic binary raster file format export routine creates two files, an ASCII header file and a binary file containing the actual grid data. When archiving or distributing binary generic raster files, make sure to include both the header file and the binary file.

Both of these export options create stand-alone files that can be moved across file systems or platforms. The files can be imported at any time, which recreates an ArcInfo format grid. Other GIS or image processing software can read these type of nonproprietary raster file formats.

 

Exporting feature themes to ArcInfo generate format

The ArcInfo generate format is an ASCII file that can be used to create an ArcInfo (vector) coverage. Because the structure of a generate file is simple, generate files are also used in many other applications that cannot handle proprietary GIS data formats.

A sample script exists in ArcView that will allow you to create generate files from shapefiles.

Generate files are formatted like these simple examples:

point generate
file format

sample file

meaning (of each line) 
1, 100, 100
2,  99, 112
3, 112, 119
4, 121, 98
5, 107, 102
...
END
 id (of point), x, y
id, x, y
id, x, y
id, x, y
id, x, y
other points
end (of file)

 

line generate
file format

sample file

meaning (of each line)
101
2,3
4,3
4,6
END
101
2,3
4,3
4,6
END
102
2,1
3,2
END
...
END		 id (of line)
x, y (vertex)
x, y
x, y
end (of line)
id (of line)
x, y
x, y
x, y
end (of line)
id (of line)
x, y
x, y
end (of line)
other lines
end (of file)

 

polygon generate
file format

sample

meaning (of each line)
701,7,7.5
3,9
4,5
8,4
9,7
6,9
3,9
END
702,20,31
19,19
18,36
31,35
27,15
END
...
END		 id (of poly), x, y (of label point)
x, y (vertex)
x, y (vertex)
x, y (vertex)
x, y (vertex)
x, y (vertex)
x, y (vertex)
end (of polygon)
id (of poly), x, y (of label point)
x, y (vertex)
x, y (vertex)
x, y (vertex)
x, y (vertex)
end (of polygon)
other polygons
end (of file)


Generate files can be used to recreate ArcInfo coverages, and if used in conjunction with exported tables, can also recreate the attribute data for coverages. You will most likely never need to use generate files, but it is a "lowest common denominator" file format if you need to brute-force a solution to import coordinates to another application

 

Exporting tables

Tables are easily exported to any of the source formats (dBase, delimited text, and INFO). Like the creation of any other file, the file type, name, and location on the file system needs to be provided during the export process. Exporting tables is performed by using the File > Export menu choice while a table is active.

 

If there are any active selections on tables, only selected records will be exported. If you want to export all records from the table, make sure to clear any active selections

A word of caution: the dBase files that ArcView uses to store data have a 10-character limit on field names. If you have created fields with names longer than 10 characters, ArcView saves only 10 characters internally, but uses field name aliases for display purposes. Exported tables will output only the internal, 10 character field names.

If you export to Delimited Text, complete field names will be exported, even if the field names are longer than 10 characters.

 

"Exporting" views and layouts

Layouts and views can be saved as graphics files by selecting File > Export while a view or layout is active. Details of this are covered in the cartography lab exercise.

The files that are created from exporting views and layouts can be used in any application that supports these types of files.

 

Exporting 3D scenes as VRML

3D views, which will be covered in 3-D Analysis and Surface Modeling, can be exported as VRML (Virtual Reality Markup Language) files, which can be loaded into Netscape or other applications that support VRML. The VRML file will look exactly like the 3D scene, including all features and symbols, offsets, and extrusions. A free VRML plug-in for Netscape and Microsoft Internet Explorer is available at Cosmo Software. Several other VRML viewers are available, such as GLView.

The VRML scene's symbology cannot be altered in the web browser, but users do not need ArcView or other specialized software in order to view and navigate the surface model.

VRML files can take a long time to generate, and the files can be very large. TINs are generally far more compact than grids when exporting to VRML. Here is an image of a 3D scene within ArcView.

And the same scene exported as a VRML file displayed within a web browser:

You can create 3D scenes and then publish them to web pages; a number of free VRML viewers exist.

Syllabus Schedule Class Meetings Assignments Course Data Internet Search

Current Grades

 Contact Us CFR 590 Internet-only section Lab Locations  
 

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