# Preferences Dialog

## Tracking Tool

The tracking tool preferences are used to control the types of information displayed by the tracking tool. This is the display area at the bottom of the Main OpenEV Window that shows information about the location pointed to by the cursor in the window.

Coordinate: Possible values are:

1. Off: Do not show the cursor position in the tracking area.

2. Raster Pixel/Line: Show the pixel/line (column/row) location of the cursor on the top most raster layer under the cursor.

3. Georeferenced: Show the cursor position in the current coordinate system of the view (which could be pixel/line, UTM, lat/long, etc).

4. Geodetic (lat/long): Show the cursor position in geodetic (lat/long) coordinates if possible. If not possible this will operate the same as Georeferenced.

Lat/Long Format: Determins the format to display Lat/Long values for the tracking tool. Possible formats are:

- ddd:mm:ss.ss Degree Minute Second notation

- ddd.ddddddd Degrees to seven decimal places

Pixel Value: Determines whether the tracker should report the top most raster layers pixel value under the cursor. Note that fetching the pixel value can be expensive for some organizations of raster file, and thus can slow down interactive performance.

## Raster

Display Georeferencing: Determines whether views loaded with a raster image should operate in georeferenced coordinates for that raster, or in raw pixel/line. A few points of note:

- The tracking tool can report georeferenced, or geodetic coordinates even if the view is drawn in pixel/line coordinates.

- The coordinate system of any vector layers must match the coordinate system of the view in order for the vectors to correctly overlay displayed rasters. Thus, only use No if vectors to be overlayed are in pixel/line coordinates, or yes, if they are in the georeferencing system of the raster.

- If the raster has GCPs, but no affine transformation, the raster will be given a first, or second order warp (depending on the number of GCPs) in order to display the raster in the projection of the GCPs. This can be fairly inappropriate for raw scenes with lat/long GCPs (such as most CEOS scenes).

Overview Sampling: Determines the sampling method to use when downsampling rasters for displays of overview images. Note that the sample method is a property of a raster, and is established at the point the raster is first displayed in a given OpenEV session based on the preferences. Changing this preference will only affect subsequently opened rasters.

- Average: Average all the pixels contributing to an overview pixel.

- Decimate: Just take one of the source pixels when computing an overview layer (the top left).

Decimation is the default, as it is less computationally expensive and gives more appropriate results when viewing complex phase images. Averaging can give much more viewable results for noisy data such as radar images. However, it makes loading overviews of large images without pre-computed overviews much more expensive because data must always be loaded at full resolution and averaged down to display resolution on the fly, whereas decimated displays often only need to load a small portion of the total available scanlines in order to compute the decimated display.

Subpixel Interpolation: Determines how a pixel is displayed close-up.

- Bilinear: The display intensity within a pixel varies from its center to its edges, based on the values of surrounding pixels.

- Off (Nearest): The display intensity within a pixel is constant.

Autoscaling Method: Determines the method used to scale an image.

- Percent Tail Trim: The intensity mapping is based on the minimum and maximum sorted data values with a user-defined percentage of the highest and lowest values not included.

- Standard Deviations: The intensity mapping is based on the mean data value plus/minus a user-defined number of standard deviations.

## Caching

Caching issues are covered in more detail in the Performance Tuning page.

File Cache: Number of bytes of memory available for caching raw raster data from disk.

GL Texture: Number of bytes of video or system memory available for caching image texturse.

## Help Browser

This tab is unavailable on Windows where the system default web/html browser is automatically used.

Enter a command to be used to display a web page containing help (such as this one). If the command includes the value "%s" then the name of the file or URL to display will be substituted for the %s. Otherwise it will be appended to the command. By default OpenEV attempts to find one of a few common web browsers.

To test a newly entered value, go to the main view window help menu and select a topic, or hit F1 over the preferences panel, after clicking outside the text box.