Basemaps within OCHRE

Every Map View in OCHRE requires a basemap. The coordinate system of the supplied basemap determines the coordinate system of the current OCHRE Map View. All other items in the view must have been georeferenced within the same coordinate system as the basemap, or they will be re-projected on-the-fly as they are added to the View.

The basemap determines both the extent and the resolution of the Map View. Items can be placed on the Map only within the geographic boundaries defined by the basemap. Similarly, the zooming capabilities of the Map in OCHRE is limited to the resolution provided by the basemap; that is, the basemap image will not pixelate in order to zoom in beyond its natural resolution. For example, in ArcMap you can right-click a Layer in the Layer pane (on the left) and "Zoom to raster resolution." This will illustrate the maximum resolution to which OCHRE will be able to zoom.

A basemap represented by a supported raster image is added to OCHRE as a regular Resource item with its Type set to "geospatial."

Important! Any georeferenced raster image used as a basemap in OCHRE MUST have a defined spatial reference. That is, the coordinate system used to plot the image in space must be explicitly set; it cannot be "undefined." For example, if viewing a raster image in ArcMap, right-click the Layer that represents the image to view its properties. The Source tab of the Layer Properties must show a properly assigned Spatial Reference (scroll past the other Raster Information to view the Spatial Reference properties). 

Alternatively, you can select one of the basemaps provided by Esri and made available through OCHRE. Note that the Esri basemaps all use the common latitude/longitude-based world coordinate system and so are mutually compatible.

The basemap identified on the Map Options of the Resource Inbox is the one that is used as the backdrop for Map View. 

Use the Set default extent option to target a specific geographic area. The basemap will be presented in a View. Use the pan and zoom controls to position the map so that the desired region is in view. Upon clicking the Set default extent button on the View menu, OCHRE will capture the coordinates of the required extent and save those for future reference.

The Map Options tab is available on all hierarchies and sets. By establishing options at the level of a hierarchy or set you override the default settings on the Resources Inbox. Views of items within such a hierarchy or set will be displayed on the basemap provided by that hierarchy or set, if any. In the event that no basemap is specified at the level of the hierarchy or set, the basemap identified on the Map Options of the Resource Inbox will be used. 

Local Basemaps

As mentioned above, OCHRE needs a project-level basemap specified on the Resource Inbox to use as the backdrop for Map View. But in the case of an archaeological project, for example, a basemap that covers the full extent of the site at an appropriately detailed resolution would likely be impractically huge. OCHRE's Map View allows you to attach a more local basemap to any hierarchy, using the Map Options of that hierarchy. Simply link in a raster image Resource as the basemap of a hierarchy and it will be available in Map View. The Information button in Map View will toggle on additional icons that identify the geospatial character of the corresponding item.