GMS:Images

An image is typically a scanned map or aerial photo in TIFF or JPEG format. Images can be imported to GMS and displayed in the background to aid in the placement of objects as they are being constructed or simply to enhance a plot. Images can also be draped or "texture mapped" onto a TIN, 2D grid, 2D mesh, or the top of a 3D grid or 3D mesh.

File:Texturemap.gif

Scanned USGS Quad Map Texture Mapped to the Top of a 3D Grid.

Image display options are changed in the Project Explorer. The options are as follows:

• Visibility - The Visibility of an Image is turned off by toggling the check box next to the image in the Project Explorer.

• Transparency - The Transparency of the images can be changed by right-clicking on the image folder in the Project Explorer and selecting the Transparency command.

• Crop Collar - USGS quad sheet collars can be removed from an image by right-clicking on an image in the Project Explorer and selecting the Crop Collar Command.

Importing an Image

Images are read into GMS by using the File | Open command. GMS supports TIFF and JPEG images.

Image Pyramids

Image pyramids can be created when an image is imported into GMS. Image pyramids are multiple resolution copies of the original image that are created and saved to speed up display. With pyramids, a lower resolution copy of the image displays quickly when drawing the entire image. As you zoom in, copies of the original image resampled at finer resolutions are then drawn. This option allows for optimal performance and clear image display.

Multiple Images

GMS allows more than one image at a time; however, you will want to insure that each image is in the same coordinate system.

Geo-Referenced Images

Some images have the coordinate system embedded in the file. Also, some images will have a separate file called a world file (for example: a tiff world file, *.tfw). These files are "geo-referenced." When these files are opened GMS automatically registers the image to the real world coordinate location specified. In the case where a separate world file is used, GMS will automatically find it and register the image if the world file has the same filename prefix as the image file and is in the same folder.

If the image file is not geo-referenced then you will have to register the image manually. (See Registering an Image)

When the GMS project is saved, a link to the image is saved in the project file, along with the current image registration information so that the image is re-registered to the same coordinates every time the project is opened. The original image file and world file (if one exists) are not altered.

Texture Mapping Images

GMS allows you to drape an image over the top of a TIN, grid, or mesh. However, only the first image listed in the project explorer will be texture mapped onto the TIN, grid, or mesh. You can change the order of the images in the project explorer by selecting the image and dragging it to a new location in the project explorer.

Image Properties

The Image Properties dialog can be opened by right-clicking on an image in the Project Explorer and selecting the Properties command from the pop-up menu. This dialog displays information about the image, such as name, path, type, pixel size etc.

Rasters

DEMs (digital elevation models), and images that include elevation data such as a geotiff, are referred to as "rasters". Using the third-party software Global Mapper, GMS supports a large number of DEM formats. DEMs are imported and displayed as images. Thus they are only displayed in plan view.

Importing DEMs

DEMs can be imported by simply opening the file(s) or dragging and dropping the file(s) into the GMS window.

Creating rasters

Rasters can be created from within GMS by interpolating from 2D scatter points. The interpolation options, the raster cell size, and the extents of the raster can all be specified in the Scatter -> Raster dialog.

Interpolating from rasters

Rasters can be interpolated to most other objects, including the z values of feature objects and to MODFLOW layers. The interpolation is done by finding the raster cells that the object's points are in and assigning the points the values from the raster cells.

Conversion from rasters

Rasters can be converted to a 2D grid or 2D scatter points.

Raster display options

The Rasters tab of the Display Options dialog is used to change the way rasters are displayed. The only options currently available are the shader which controls the color ramp, and whether to enable hill shading (shadows). These options are from Global Mapper.