VEC

IDRISI vector format in .vec files.  VEC files do not automatically provide coordinate system information.   VEC files are often accompanied by .txt or .dvc files that provide documentation.  Such files can be useful for the detective work involved in figuring out what coordinate system a VEC file is supposed to use.

 

 

To import from VEC format:

 

  1. Choose File-Import from the main menu.

  2. In the Import dialog browse to the folder containing data of interest.

  3. Double-click the file ending in .vec for the data of interest.

  4. A table and a drawing will be created.

 

 

We can double-click on drawings that are created to view them.   For a more interesting display, we first create a new data source using a Bing street maps image server as shown in the Example: An Imageserver Tutorial topic.   We then create a map and drag and drop the Bing layer into the map, and then we drag and drop a drawing into the map.

 

 

The drawing appears without using the correct projection, which we can infer by guessing that the data does not involve country outlines in the ocean off the coast of Africa..   That is a good reason to avoid using VEC format whenever possible, to avoid the tedious work of finding out what coordinate system is supposed to be used and then assigning it.   

 

In this case, we might be able to discover the intended coordinate system by reading the accompanying .txt file.

 

 

Opening the .txt file in Notepad, we scroll down to discover the data set uses Lambert Azimuthal Equal Area projection.      The .txt file also seems to specify the various parameters required to specify this projection.   To do that, in the Components pane we click on the coordinate picker button for the drawing and we choose the Assign Initial Coordinate System command in the resulting menu.

 

We then choose More... to get the Coordinate System dialog:

 

 

In the Coordinate System dialog Custom tab we choose Lambert Azimuthal Equal Area as the Type, and we specify 60 for the Center Latitude and 20 for the Center Longitude, reading both values from the comments in the .txt file.   The Base must be adjusted to use the ellipsoid/datum specified, which the .txt file refers to as a "spheroid."   We click the picker button to specify a new Base.

 

 

In the Base Coordinate System dialog we enter International in the filter box to reduce the very long list of standard bases to only those with "International" in their names.   There is no "International 1909" as mentioned in the .txt comments.

 

Manifold knows virtually every ellipsoid/datum ever used, so usually when a GIS data set specifies the name of an ellipsoid not found in Manifold the name specified is a synonym for whatever is the name listed in Manifold.   Manifold lists standard names as currently used by standard setting bodies such as EPSG and modern governments, which at times use more modern names for ellipsoids that many years ago were known by different names.

 

We spend a few minutes on an Internet search using our favorite search engine, and discover that the "International 1909" ellipsoid was also known as the "Hayford ellipsoid," which in turn was renamed the "International ellipsoid 1924" after being adopted by the International Union of Geodesy and Geophysics IUGG in 1924.  Comparing the major axis of the International Reference 1924 choice in Manifold (which uses modern, EPSG nomenclature), 6378388, we see it is the same as the "radius" for the "spheroid" cited in the .txt, so that is what we will use.  We click International Reference 1924 and then press OK.

 

 

Now that we have selected a new Base, we can click OK to assign the new initial coordinate system to the drawing.

 

 

Immediately, the objects in the drawing move to the correct, georeferenced position.

 

 

We zoom in and use the Style pane to color the areas, and the Layers pane to apply some transparency.   We see the drawing shows the drainage basin for water draining into the Baltic Sea.

 

See Also

Projects and .map Files

 

Tables

 

Drawings

 

Maps

 

Images

 

Style

 

Projections

 

Assign Initial Coordinate System

 

Repair Initial Coordinate System

 

Reproject Component

 

Map Projection

 

Coordinate System

 

Base Coordinate System

 

Favorite Coordinate Systems

 

Favorite Base Coordinate Systems

 

Lambert Azimuthal Equal Area

 

Example: Assign Initial Coordinate System