Background

This task allows you to import or download more background imagery for your site from a large variety of formats.

Import a georeferenced image For importing image files that contain georeferenced meta-data (i.e. they have a location and area). They will be placed in the correct location on the map
Download imagery Download imagery from various online sources.

In order to load a background image you currently need to create a Global Mapper world file and save it in the same folder as the image. This lets WindFarmer know where the image is located within it's projection system.

If the co-oridinate system of the background map is different to that set for the workbook in the [Site Location] then you need to create a .prj file to accompany the image so the transformation is performed on import.

World file format

World file format The Global mapper Generate World File option results in a world file being generated in addition to the image.

The image-to-world transformation is a six parameter affine transformation of the form:

$$x' = Ax + By + C$$ $$y' = Dx + Ey + F$$

where

  • x' = calculated x-coordinate of the pixel on the map
  • y' = calculated y-coordinate of the pixel on the map
  • x = column number of a pixel in the image
  • y = row number of a pixel in the image
  • A = x-scale, dimension of a pixel in map units in the x-direction
  • D,B = rotation terms.
  • E = y-scale (this value is always negative, because image space is top-down, whereas map space is bottom-up)
  • C = translation term; x-Origin (x-coordinate of the center of the upper left pixel)
  • F = translation term; y-Origin (y-coordinate of the center of the upper left pixel)

The transformation parameters are stored in the world file, an ASCII format, in this order, A, D, B, E, C, F; for example:

2.22123393184959 ( A )

0.00000000000000 ( D )

0.00000000000000 ( B )

-2.22123393184959 ( E )

10383.13600759092515 ( C )

11611.48117990907485 ( F )

Note that the parameter characters are included in the example for clarity. They do not actually appear in the file.

Naming convention

The world file should be stored in the same directory as the image and will have the same primary name as the image. The filename extension will depend on the selected image type (JPEG=.jpgw, PNG=.pngw, TIFF=.tfw,BMP=.bmpw).

Corresponding world file extension for each image file extension... bmp - bmpw or bpw jpg - jpeg jpgw or jgw tif - tff; tiff tfw gis - gsw lan - lnw bil - blw bip - bpw bsq - bqw sun - snw rs - ras rsw rlc - rcw