Shorelines and Islands

Shorelines and Islands (Map Boundaries)

Map boundaries are polygons that can be added to a map project to define the region in which the map is created. Map boundaries can, optionally, also provide depth information that is used during map generation.

The typical use for map boundaries is to define the shoreline and islands of a body of water, with a known depth of zero. The zero depths associated with the shoreline are included in the map calculation as if they were recorded track-points, enabling depth values to be interpolated between the shore and recorded track-points.

Shorelines and islands

·Each map boundary can be either a shoreline or an island.

·There can only be one shoreline per map project, with an unlimited number of islands.

·The shoreline boundary excludes all data that is outside of it.

·Island boundaries exclude all data that are inside them.

Adding and Editing Map Boundaries

Map boundaries are displayed, and can be edited in, the tracks and boundaries view of a map project:

Editing functions for map boundaries, including a list of all of the map boundaries in the current project, can be found under the Map Boundaries section of the project edit panel:

1. Map boundary list

Map boundaries are shown in a list, which each row representing a separate boundary. The boundary name (optional) and type is shown.

2. Boundary operations

·Use the New button to create a new boundary, which will open a new polyline component for editing in the map display area (see Editing Map Layer Components for more information on editing component geometries). Once the geometry has been created and saved, it will be added to the boundaries list.

·Boundaries can be imported using the Import button. Compatible file types are ESRI Shapefile (polygons or paths), GPX and KML/Z (Google Earth). ReefMaster will look for path components within any selected file, and import all of them as map boundaries.

Important: Map boundaries are always imported as islands. This is because multiple islands are allowed per map, but only a single shoreline. Make sure to examine any imported boundaries and set the appropriate shoreline, if required.

·One or more selected boundaries can be deleted by using the delete button.

3. Boundary details

When a boundary is selected in the boundaries list, details for that boundary can be edited in the boundary details section.

·An optional name can be provided for the boundary to assist in identifying the boundary in the list view.

·The boundary type can be changed between island and shoreline. Note that only one shoreline is allowed per map.

·When checked, Provide Depth means that points along the boundary will act as a depth data source during map generation. Typically, map boundaries are shorelines and assume a depth of zero. The actual depth provided by the boundary can be edited as required.

Creating Boundaries From in Google Earth

Tracing shoreline outlines in the Google Earth application is a good way to create boundaries:

·Trace the required boundary in Google Earth as either a polygon or a path. Both polygons and paths are treated the same in ReefMaster, which considers all boundaries to be closed loops.

·Save the polygon or path object; ReefMaster supports both KML and KMZ Google Earth file formats.

·Import the boundary into ReefMaster by following the import process described above.

Tracing boundaries in the field - the most accurate source of map boundaries

On-line map sources such as Google Earth can be very good, but are not always absolutely accurate. The most accurate way to create a map boundary is to walk a shoreline with a hand-held GPS unit and record the trail. It should be possible to convert the recorded track to a GPX file, which can be imported into ReefMaster for use as a boundary.

Using a vector component as a map boundary

Any vector component (polyline, contour, polygon or isobath) from any map project can be employed as a map boundary simply by copying and pasting the component from a map view into the tracks and boundaries view.