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How to use HRSCview

HRSCview is a web interface to the Mars Express HRSC image archive at the Freie Universitaet Berlin. It carries out on-the-fly image subsetting, stretching, compositing, and the the case of perspective views, projection of map-projected data-products. Access to the images is provided through a footprint map, by coordinates or by image identifier. The site is provided jointly by the Freie Universitaet and the German Aerospace Center (DLR).

View mode

You can switch between the image footprint modes (all images, archive DTMs) and one of the image modes (Nadir, Elevation, or one of the colour modes) using the radio buttons. The same coordinates apply to both views, but note that the scales are selected independently: the map scale for the images, and the footprint scale for the footprint views.

Navigation

There are three ways to select a region of interest using HRSCview:

- click in the image or footprint map: the view will be recentred, and the coordinates of the point you clicked will appear in the latitude/longitude boxes. Clicking beyond the edge of an image will take you into an adjacent image if there is one

- enter the desired surface coordinates into the latitude/longitude boxes: the view will be recentred on the chosen point

- if you know which image you are interested in, enter its number directly into the Identifier box. The view will centre on the image

- at surface points covered by more than one image, the image identifier box will contain a list of the images to select from

Footprint view - all images

The footprint view displays the coverage of the Martian surface by released HRSC images. Bright areas have been imaged, the level of the brightness giving an indication of the image resolution: the brighter the area, the higher the resolution. The background map is derived from MGS MOLA altimetry. After clicking on an image the identifier will also be seen in the identifier box.

Footprint view - archive DTMs

This shows the footprints of images for which archive-quality DTMs (digital terrain models) are available for download. The higher resolution DTMs can be explored using HRSCview and, if desired, downloaded via the product page. To access this page, select the image and click the Image Identifier link. These data-products are currently available only in VICAR format, compressed with gzip.

Map scale

The map scale is selected in metres/pixel as shown on screen. The scale bars are likewise true to the image as shown (for the footprint map, the scale bar show the equatorial scale). The pixel scale and other parameters of the original image may be found by clicking on the Identifier link after selecting an image.

The elevation scale bar, when present, shows the elevation range of the current view, i.e. the range between the minimum and maximum surface altitudes.

View size

Pick a size from this list to determine the size of the viewing window. Sizes are given to suit common monitor dimensions, both landscape and portrait. Note that many browsers allow you to increase the viewing area by pressing F11.

Image modes

There are seven image modes:

- nadir, the highest resolution, downward-looking channel of HRSC

- elevation, a colour-scale stereo-derived DTM (for archive DTMs only)

- nadir-DTM, the nadir channel colourised with the stereo-derived DTM

and five colour modes where the nadir channel colourised with three colour channels (R-G-B or IR-G-B) via an HSV transform. The image has the same detail resolution as the nadir mode, but its colour resolution is typically somewhat lower:

- Mars-like: a predefined stretch intended to give an approximation to the colours which might be observed at the surface

- raw: each colour channel presented as captured by the camera

- stretched: each colour channel stretched independently

- enhanced: each colour channel stretched independently and then squared, to enhance colour differences

- ratio: the three ratios ir/r, r/g, and g/b stretched independently and presented as an r-g-b composite

Contours

Show elevation contours (not for quick-look DTMs)

Substitute IR for red

Selecting this box causes the colour composite to be made up from the infra-red, green and blue channels instead of the usual red, green and blue channels.

Perspective views

Transforms the view from nadir (overhead) to a simulated perspective view, looking in any of the four directions: north, east, south, west. The vertical exaggeration can be varied using the drop-down list. A value of 1 shows the relief in its true proportions.

Update view

After making changes to the image settings, press the Update view button to generate a fresh view.

Scale bars

The grey scale bar indicates the distance scale in the current view. The colour bar, when present, indicates the range of altitudes in the present scene.

Download

When there is a valid image identifier in the box, a download link appears, which brings up the science data-product page. From there it is possible to download full image strips.
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Updated: 06.03.2007