3.3 Viewing single images and mosaics

---

---

Viewing images in image database is done by double-clicking on the image in the Downlink selection tree to open an Image view. An example of an Image view is shown in Figure 3.2. When you open the view, it will appear in an empty view pane if there is one, or in place of the least recently selected view. You may also open an Image view by dragging and dropping an image from the Downlink selection tree onto a view pane or onto a viewgrid tab (see Section 3.2).

Selecting which image to view

When you open an Image view, the default image is shown in the view. For groups of images such as left/right stereo image pairs or images from different color filters (such as from Pancam) you can select an image to view from the Image menu. Left/right images from a stereo pair are labeled “left” and “right”. Images from different color filters are labeled “left1”, “left2”, etc. according to the Pancam filter numbers. When Pancam red, green, and blue filters are used together, a color composite image is also made, such as “left2_5_6” for filters 2, 5, and 6. If a red, green, or blue filters isn’t available from the left Pancam, no color image will be available on the Image menu. For an instrument that is a single camera the image will be labeled “mono” (monoscopic).

3.3.1 Panning and Scrolling

If the image at full size is larger than the view pane, scroll bars will automatically appear. To view an unseen area of the image, click and drag the scroll bar in the direction of the unseen area.

The Pan cursor is also a convenient way to pan the image. To use it, click on the Pan button on the toolbar.

The cursor will change to a hand cursor when the mouse is over the image. Click and drag with the hand to slide the image in any direction as if it were a piece of paper sliding on a table. (You can also select the Pan cursor from the Action menu.)

3.3.2 Resizing the image

When you first look at an image in Image view, it is shown at full size. There are several ways to zoom in and out of the image to resize it to a useful size for your work.

3.3.3 Information from images

The Image view will give you a lot of useful information about the image you are viewing. This information is displayed in the Downlink Browser’s info pane in the lower left corner in the lower left corner of the browser (see Figure 3.3):

---

---

• Rover Position: The XYZ position of the rover in meters where the image was captured and the heading of the rover in degrees is displayed here. The position and heading are given in the coordinate frame of the site that was active when the image was captured.
• Selected point: position in meters, surface normal, range in meters, azimuth in degrees and elevation in degrees are given if the image is from a stereo image pair. (For stereo image pairs, correlation analysis creates a range map that contains distance to each pixel in the image. ) The position, surface normal, and azimuth are given in either site frame or rover frame. The frame used to report these values is selectable by choosing “SITE” or “ROVER” from the Frame pull down menu located above the info pane.
  

  The elevation of the pixel is given in the rover’s mast coordinate frame. The surface normal is a normalized vector (magnitude 1) that results from a surface fit to the 3D surface, indicating the orientation of the surface at the point in question. The normal points outward from the underlying surface. The range (distance) to the point is in the rover coordinate frame. The pixel coordinates of the selected point (labeled “I,J”) are listed along with the image ID of the image that was selected. The cursor position in the view is also displayed (always the same as the I,J pixel coordinates for a single image, but may be different for a mosaic image). Lastly, the pixel value(s) are listed for each of the one or more bands of the image.

• Ruler: if a ruler has been used in an image, the distance between the endpoints in meters, starting and ending position in meters, and starting and ending view coordinates are displayed. The starting and ending 3D positions are reported in either site frame or rover frame depending on which is selected in the Frame pull down menu located above the info pane. (See Section 3.3.4 for more information about the Ruler tool.)
• Image size: The width and height of the image in pixels and the number of bands (1 for greyscale, 3 for color, etc.) are displayed.

3.3.4 Selecting points

Query cursor

The Query cursor is the cursor that you have when you first load up an Image view. The cursor is pointer-shaped, and when you click once on a pixel in an image a Point of interest glyph is created. (Glyphs are what we call small icons, labels, or other graphics that annotate images.) The Point of interest glyph has a number of important features:

• When you select a Point of interest in one view, that same point is displayed in every other open view that also contains that point. This is useful for comparing one area imaged from two different points of view, or locating a particular image in a mosaic.
• The Point of interest is used to create Features and Targets for Activities (see Section 4.2.1).

Also, the appearance of the Point of interest tells you a lot about the location:

Region tool

The Region tool is useful for selecting a rectangular area of an image. To use the Region tool, select the Region icon on the toolbar or select it from the Action menu. Once Region is selected, click and drag a box in the image to indicate a region of interest for purposes of discussion.

Ruler tool

The Ruler tool is useful for measuring distances between two points. For instance, if there are two tall rocks in the direction that you are considering whether to drive, the ruler can measure how far apart they are to see whether the rover will fit easily between them. Or perhaps you are analyzing a rock in front of the rover and want to measure its size to see whether a particular instrument is suitable to place on it.

To use the Ruler tool, select the Ruler icon from the toolbar or select it from the Action menu. Once Ruler is selected, click and drag from one point in the image to another. If the starting point and ending point both have 3D information available, the Ruler glyph (a yellow line) will appear in the image. The Ruler glyph will also appear in every other open view that contains one or both of the selected points. The distance between the two points and their locations in 3D and pixel coordinates are displayed in the Downlink info pane.

Since 3D information can vary in accuracy in an image depending on the nature of the texture, etc., it is wise to try to measure distances several times, selecting slightly different endpoints for the ruler and comparing the distances that you see. If there are outliers (a value that is very different from others a set of reasonable values) then you can take the median distance of a set of measurements as a better estimate.

3.3.5 Azimuth/Elevation angle display

Many images have associated pointing information that are displayed in Image view in the Azimuth angle display and Elevation angle display. Figure shows an example of an image with both an Azimuth angle display and an Elevation angle display. The Azimuth angle display shows angles increasing in the direction you would turn your head right (clockwise) if you were standing at the rover’s position. The Elevation angle display shows angles increasing in the direction you would tilt your head upward if you were standing at the rover’s position, with 0 degrees looking straight ahead (no tilt). Both angles are displayed in degrees.

---

---

The azimuth angle may be displayed in either site coordinate frame (0 points north) or rover coordinate frame (0 points along the rover’s heading).

By default the coordinate frame is site frame, but you can select the frame of the Azimuth angle display using the Azimuth pull down menu. To check what the frame is that is currently shown, also look to the extreme left of the Azimuth angle display for the letter “S” for site or “R” for rover.

3.3.6 Mosaic views

There are several mosaic views that you can use to view an entire scene at once where the rover has stopped to take images in every direction. The Cylindrical Mosaic view mosaics a set of images as if onto a large cylinder surrounding the rover, similar to Mercator maps of the world that you are used to seeing. The Azimuthal Mosaic view shows a bird’s-eye view of the scene with the rover in the center and north pointing up in the image, similar to a map of the world looking down onto the North pole. The Panorama view puts together the images in a scene in a montage fashion, as if each image was pasted onto a wall like a collage. In the following sections we will discuss each Mosaic view in detail.

Opening a Mosaic View

To open a Mosaic view, you select a collection item from the Downlink selection tree. The collections folder is always contains folders for each site (each major destination that the rover visits). Within a site, the rover drives through a number of positions, which are all numbered starting at 0. The items in the collections-¿sites folder are named by instrument and the position number within the site. If the rover takes a Navcam panorama as soon as it reaches a new site (which it often does), The collection would be called “NAVCAMWedgeSet-position-0”. The term “wedge” refers to a single image. Each image in the collection looks in a particular direction, and the collection can be thought of as a large pie with the rover in the middle. In that sense, a single image is one wedge of the entire pie, and “wedge set” is the whole set of wedges.

---

---

Cylindrical Mosaic View

The Cylindrical Mosaic view is the view that you see when you drag and drop a collection item from the Downlink selection tree to open a view. An example of this type of mosaic is shown in Figure 3.5. This creates a 360^omosaic, with 0 pointing north. Like in the Image view, you can switch the Azimuth angle display between displaying direction in site coordinate frame (north-aligned) to rover coordinate frame (0 degrees pointing in the rover’s forward facing direction.) (see Section 3.3.5 for more on this.) The elevation display on the left side of the mosaic shows 0 pointing level with the ground, 90 degrees pointing straight up, and -90 degrees pointing straight down.

Viewing One Image from the Mosaic

When you are viewing a mosaic and you are interested in one particular image, you can directly open that image in its own Image view. To select an image to view, click on any pixel in the image to place the Point of interest cursor inside it and then select the Open Selected Wedge menu item in the Action menu. It is usually a good idea to configure your browser for multiple view panes before opening an individual Image view from the mosaic to prevent the Mosaic view from being replaced when the new view opens.

Setting the Mosaic Start Angle

If you are viewing a mosaic and a particular area of interest happens to fall near the left edge or right edge of the image, you can reset the starting azimuth angle of the mosaic to split it at a different location and reposition the area of interest nearer to the center of the image. To set the mosaic start azimuth angle, select the Set Start Angle menu item from the Action menu and a dialog will appear asking you to enter a new angle in degrees (between 0 and 360 degrees is recommended). When you click Ok, the mosaic will repaint, shifting the images with respect to the start angle you entered.