Monday, June 27, 2011

Create a grid tile layout using Global Mapper

A region of interest may cover a large area. The file sizes of Geospatial data such as LiDAR or aerial photographs acquired over the entire region of interest will obviously be too large to be stored as a single physical file. In order to work with the data, geographers will have to cut the data into manageable tiles. For this purpose, a grid tile layout with some sort of naming scheme and dimensions will have to be designed and created.

An example of a tile layout is shown below. In this example, the tiles are named according to the lower left coordinates i.e. X_Y, where X = x coordinate divided by 1000 and Y = y coordinate divided by 1000; and a tile has a width of 2000 meters and a height of 2000 meters.

Global Mapper can be used to create the grid tile layout from a region of interest polygon.
  1. Start Global Mapper. Load and display the region of interest polygon.
  2. Press ALT+C to display the Overlay Control Center.

  3. In the Overlay Control Center, select the region of interest layer. Click Metadata.

    The Metadata dialog box appears.

  4. Take note of the UPPER LEFT X, UPPER LEFT Y, LOWER RIGHT X, and LOWER RIGHT Y attributes.
  5. Since the UPPER LEFT X value is 305458, an appropriate grid origin x value would be 305000, i.e. a round down.
  6. Since the UPPER LEFT Y value is 2119255, an appropriate grid origin y value would be 2120000, i.e. a round up.
  7. Since the difference between the LOWER RIGHT X and UPPER LEFT X is 55326 (360784 - 305458), then an appropriate number of grid columns would be 28, i.e. 55326/2000 where 2000 is the grid width.
  8. Since the difference between the UPPER LEFT Y and LOWER RIGHT Y is 41187 (2119255 - 2078068), then an appropriate number of grid rows would be 21, i.e. 41187/2000 where 2000 is the grid height.
  9. Close the Metadata dialog box.
  10. Select ALT+D. Click the Create Regular Grid of Features  icon.

    The status bar shows the message "Left Click to Select Grid Anchor Point, ...".
  11. Click a point anywhere inside the map window.

    The Grid Setup dialog box appears.

  12. In the Number of Grid Rows field, type in 21.
  13. In the Number of Grid Columns field, type in 28.
  14. In the Grid Cell Width field, type in 2000 meters.
  15. In the Grid Cell Height field, type in 2000 meters.
  16. Click Anchor Point.

    The Select Location dialog box appears.

  17. In the X Coordinate field, type in 305000.
  18. In the Y Coordinate field, type in 2120000.
  19. Click OK.
  20. Toggle on Separate Row/Column Letters or Numbers. Toggle on Numbers.
  21. In the Rows Start field, type in 2120. In the Rows Step field, type in -2.
  22. In the Columns Start field, type in 305. In the Columns Step field, type in 2.
  23. Toggle on Reverse Naming, Prepend 0, and Separate Rows and Columns with Underscore.

  24. Click OK.

    The grid tile layout is created.

No comments:

Related Posts with Thumbnails