The "Visual" tab visualizes the selected variable. The image is initially shown in the native Coordinate Reference System (CRS) of the data, but can be reprojected. User can pan the raster, zoom with mouse wheel or rotate with keyboard (Alt + arrows). Colors can be modified by clicking on the "Colors" title on the left side. The screenshot below shown an example.

Credit: raster data shown in this page were taken from G-Portal by Japan Aerospace Exploration Agency (JAXA).

The above GCOM-C raster data uses more than one value for representing missing data. The kinds of values are listed in the "Category" section and are (for that example): "Missing", "Retrieval error", "Cloud" and "Land". Each kind of missing value can be assigned a different color by clicking the corresponding cell in the "Colors" column. In above example, we assigned a green color to missing values of "Land" category. This action caused a few islands to become visible in the lower-right corner.

Coordinates and data values under mouse cursor

By moving mouse cursor over the image, user can see the temperature value in °C together with geographic coordinates (see lower right corner in above screenshot). If the mouse cursor is over a missing value, the category name (e.g. "Cloud") will be shown. The Coordinate Reference System (CRS) used by the status bar can be changed independently of image CRS by clicking with the right mouse button on the status bar. For example it is possible to view the image in a Mercator projection and still show mouse positions with geographic coordinates.

Coordinates precision

The coordinates shown on the status bar use the minimal amount of fraction digits needed for separating two screen pixels at current zoom level. This precision varies with map scales: user can see the number of fraction digits increasing during zoom-in, and conversely during zoom-out. This calculation works even if the image and the status bar use different map projections. For example the number of fraction digits may increase when the mouse moves toward a pole (depending on the map projections).

The process of transforming mouse coordinates to raster coordinates to status bar coordinates may be complex. If that chain involves a datum change, then the results have an uncertainty which can be anything between a few millimeters to a kilometer. If the uncertainty is smaller than the precision of coordinates shown in the status bar, then the accuracy is not provided. But if user zooms enough, the coordinate precision may become finer than positional accuracy. In that case a text such "± 1 m" appears. Screenshot below is an example with the status bar showing coordinates in a Mercator projection. A 3 kilometers uncertainty seems high, but it is because no datum shift information is available in this example, in which case Apache SIS assumes a worst case scenario.

Raster reprojection

The raster can be reprojected to different Coordinate Reference Systems (CRS). For applying a reprojection, click with the right mouse button somewhere on the image. The click location is significant, because Apache SIS will adjust zoom and rotation after reprojection for minimizing visual changes around that point. The contextual menu offers two ways to choose a CRS: the first way is the “Reference system” menu item, which offers a list of predefined CRS. If the desired CRS is not in the initial short list, click on “Others” for choosing among the +6000 CRS supported by Apache SIS. (Note: this list is available only if the EPSG geodetic dataset has been installed, which is not the case by default for licensing reason). The “Filter” field can help to find the desired CRS. The dialog box shows a warning in red if the selected CRS does not have a domain of validity intersecting the raster geographic area. Example:

The second way to select a CRS is the “Centered projection” menu item. It offers projections configured for the location where mouse click occurred. For example if the “Universal Transverse Mercator” (UTM) sub-menu is selected, Apache SIS will chose automatically the appropriate UTM zone. It often makes shapes more recognizable. In the example below, the raster become more rectangular when choosing a CRS adapted to its location on Earth. The CRS name is displayed in the lower-left part of screenshots.

Note: an interesting choice offered by “Centered projection” menu item is “Azimuthal equidistant”. When choosing this sub-menu item, the mouse click position become the map projection center. Distances and angles measured from that point are corrects (but only from that point, not between arbitrary pair of points). See Wikipedia for more information.