Mapping: Managing Point Coordinates

By Sandra Schloen, May 2014

Updated December 2017

Using a georeferenced raster image in the built-in OCHRE Map viewer, you can easily and interactively assign map coordinates to database items. This is particularly useful for specifying findspots for artifacts from georeferenced top plans.

  • Begin by creating or linking into your taxonomy a Variable of type "coordinate." This is a special variable type that expects an x and y, and optionally z, decimal value. See Variables of Type Coordinate.

  • Create a Predefinition that includes the coordinate-type variable created above. This may or may not include other properties. The predefinition should contain only one coordinate-type variable (if others are present then only the first will be used).

  • Create a Resource for a georeferenced raster image. Be sure that the image is tagged as a "geospatial"-type resource. View this image. It will be displayed using OCHRE's integrated Map viewer.

  • In the Map viewer, use the picklist provided on the Map viewer toolbar to select the Predefinition created above.

  • Use the Linked Items pane to find the database item whose coordinates you wish to assign. For example, find the "Locations & Objects" item using the "Find by name" feature and select it using the checklist feature of the Query Results pane. Alternatively, navigate to the required item in the appropriate hierarchy in the Linked Items pane.

  • Click the "Identify Coordinate" tool from the Map viewer toolbar. The cursor will become a cross-hair. Position the cross-hair at the required location on the map and click. OCHRE will capture the x and y coordinate values at the mouse-click location.

  • OCHRE will prompt you to enter the optional z-value for the coordinate. For artifact find-spot locations, for example, this would typically represent an elevation. If no z-values are being entered you are given the option of suppressing subsequent prompts for z-values.

  • OCHRE will have you confirm the value of the given property being assigned to the selected item. Upon confirmation this property will be merged with any other properties of this item and posted to the database. If the property-variable already exists a new instance of it will be added (that is, it will not overwrite existing values). If an observation is needed (that is, if the item has not yet been described using any properties) it will be created automatically.

  • Repeat as necessary, selecting appropriate items from the Linked Items pane and clicking on their coordinate locations. Note the toggle button on the toolbar that lets you turn on grid-lines, drawn at integral-intervals based on the map unit across the extent of the map both horizontally and vertically, to help locate coordinates..

Coordinate property values will display appropriately, to two decimal places, in the item's View. In addition, items included on the view of a query-based map will plot their coordinate locations appropriately.

Copying Point Coordinates

(since summer 2017)

Point coordinates can be copied from one item to another. An archaeologist may want to do this, for example, to assign the closing elevation(s) of a locus of excavation to be used as the opening elevation(s) of a new locus.

  • Begin by bringing into view the elevation points to be copied.

  • Zoom in far enough to be able to distinguish and select the point(s) you wish to copy.

  • In the navigation pane in the left-most panel, select the item to which the points are to be assigned.

  • In the Predefinition pick-list, select a predefinition to be used to assign the point(s). Be sure to choose a predefinition that includes an appropriate coordinate-type property.

  • Click the x,y-marquee coordinates button to activate its selection mode. Click-and-drag to select the point(s) to be copied. OCHRE will copy only visible points.

  • OCHRE will display a confirmation message, indicating the action that will be performed; confirm or cancel. If you proceed, the selected coordinates on the map canvas will be assigned to the currently selected item in the navigation pane.

OCHRE will avoid copying duplicate points, for example, if it is difficult to avoid selecting redundant points that are clustered closely together. We also mention this because the item will plot itself on the map as a confirmation of the success of the action, in effect dropping its new points directly on top of the original ones. Keep this in mind as you toggle items on/off in the View.

As a result of copying the points, the coordinates are assigned to the item using the given predefinition. If there are any problems, these can be edited manually, or removed in the usual way (by any user with edit access).

[Option to Use a Point Shapefile as the Source of Coordinate Data -- out-of-date]

As a alternative to clicking coordinate locations with a mouse, if you already have a point-based shapefile that contains points at the required coordinates, these points can be used instead.

  • View the point-shapefile as an OCHRE resource and select the layer that contains the points. The Feature Selection tools will become active.

  • Use one of the Feature Selection tools to select the required point (e.g. circle it with the Circle tool).

  • As above, use the Linked Items pane to select the OCHRE item to which this point's x- and y-values are to be assigned.

  • Click the Identify Coordinate tool. This time, because you have already identified a point coordinate, this coordinate's x- and y-values will be assigned to the currently selected item. You will be prompted, as above, for the z-value, if relevant. You will also be prompted to confirm the assignment of the coordinate values to the currently selected item.

  • Repeat as necessary to assign the coordinates of other point shapes to their respective items.