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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 System (CRS) can be selected among the list of CRS 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. This (Note: this list is available only if the EPSG geodetic dataset has been installed, which is not the case by default for licensing reason (a future version may provide a plugin download mechanism for easier installation). 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:

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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.Image Removed