What's New with MapInfo
Continued ...

Grids



Grid themes were added to MapInfo Professional in version 5.5. This type of theme displays data as continuous color variations across a map. The map is created by the program interpolating point data from a source table, and then generating a grid file based on the interpolation and displayed as a raster image on the map. The data is projected onto grid cells, with values based on the point data that falls within each cell and estimated values for cells with missing data. Through its continuous shading, this type of map allows you to infer a value where no information is available.

Triangulated Irregular Network (TIN) Interpolator

Previous versions of MapInfo Professional only allowed for one type of interpolation for creating Grid Thematic maps. Version 6.5 adds the TIN Interpolator. There are now two methods of creating or interpolating grid thematic maps. This technique resolves irregularly spaced data into a set or triangles that connect nearest neighbors.

The TIN Interpolator Settings dialog allows the user to control the following: Cell size, Tolerance, Distance, and Feature Angle. Tightening these settings can drastically increase the amount of processing time required to process these maps, but can also greatly improve the resolution of your resulting map.

There many interpolation algorithms or techniques available and each has its own pro's and con's. The techniques range from simple to highly complex. They can take a long or short time to process. Most of the issues with the different algorithms center on the type or amount of "artificial features" the griding algorithm creates. MapInfo now includes two of the most commonly used algorithms and there are hooks in the program that would allow you to write and add your own algorithm.

Grid Handlers

MapInfo Professional 6.5 has added three new grid handlers to support direct reading of grid files. These formats are DEM-USGS Text (.dem), GTOPO30 (.dem), and DTED levels 1,2,3(.dt0, .dt1, .dt2). The addition of these handlers should allow users to take advantage of terrain data that already exists, much of which is free.

To the right is an example DTED level 0 file from NIMA. The file is a section of southern Nevada. With MapInfo, there is a new file format type added to the Table Open dialog allowing selection of these new file types. Once open, these files can now be worked with as an additional map layer.

Check out the following websites for finding some of these data files:

DTED files (Digital Terrain Elevation Data)

A DTED file is a simple, regularly spaced grid of elevation points similar to USGS DEM files, but originally designed by NIMA for military applications.

There are 3 type of DTED files that MapInfo will read:

  • Level 0 - file extension .dt0, post spacing is 30 arc second (~ one kilometer)
  • .Level 1, - file extension .dt1, post spacing is 3 arc seconds (~ 100 meters)
  • Level 2, - file extension .dt2, post spacing is one arc second (~ 30 meters)


Note: Level 1 and 2 are "Not releasable outside DoD unless specifically authorized by the HQ NIMA"

GTOPO30 Files

GTOPO30 is a global digital elevation model (DEM) developed by the U.S. Geological Survey's
EROS Data Center. The data has a horizontal grid spacing of 30 arc seconds (approximately 1 kilometer). GTOPO30 was developed to meet the needs of the geospatial data user community for regional and continental scale topographic data.

DEM - USGS Text Files

The USGS Digital Elevation Model (DEM) data files are digital representations of cartographic information in a raster form. DEMs have a sampled array of elevations for a number of ground positions at regularly spaced intervals. These data files are produced by the U.S. Geological Survey as part of the National Mapping Program.

The U.S. Geological Survey produces the following main types of DEM data:

Large scale 7.5 minute DEM
Large scale 15 minute
Intermediate scale 2 arc second (also known as 30 minute)
Small scale 1 degree units.


About the Author:

Angela Whitener is the Vice President of Software Development for IntelleVue, a MapInfo strategic partner in Tulsa Oklahoma. She has over 15 years of software development experience, with the last 10 being focused on developing solutions using MapInfo technology. She has presented GIS technology papers and speeches at GIS conferences and co-authored four MapInfo books.

MapInfo Unveils Significant Visual Enhancements to MapInfo Professional v6.5

Comments? Feedback? Click here to tell us what you think about this topic or if you have additional information you'd like to share on this subject!



Popularity Rating for this story - ">