The OSGR Tool for QGIS | Biodiversity Projects

The OSGR Tool for QGIS

This is the help for version 3.n.n of the FSC QGIS plugin which is compatible with version 3.n.n of QGIS. If you want to see the help pages for version 2.8.0 of the plugin, which was the last release compatible with version 2.n.n of QGIS, then follow this link: FSC QGIS plugin for version 2 of QGIS.

QGIS is international in scope and not specifically geared up for the UK context. Although it handles the British-specific CRSs very well, it does not handle the unique OS grid referencing system that we have in the UK. This means that although it understands eastings and northings perfectly well, e.g. the location of the FSC Preston Montford bar which is easting 343292 and northing 314369, it doesn’t understand the equivalent 10 figure grid reference, which is SJ4329214369.

But biological recorders and GIS users operating in the UK  frequently need to deal with OS grid references, e.g. to centre a map on a given grid reference or to find the grid reference at a certain point and creating grids corresponding to OS grid squares. The QSGR Tool provides these functions to QGIS users.

OSGR toolbuttonOSGR Tool for QGISTo start the OSGR Tool, click the relevant button on the FSC QGIS plugin toolbar. By default, the OSGR Tool docks initially at the bottom left of the QGIS window (below the layers panel if you have that opened and docked on the left-hand side). 

The grid reference at the current mouse cursor position is displayed in the tool. By default, this changes as the mouse moves, but this behaviour can be altered so that it changes only when the mouse is clicked in the map view by checking the on click checkbox. If the show grid square checkbox is checked then the grid square corresponding to the displayed grid reference is shown in the map view. The precision of the grid reference displayed is controlled by the drop-down list at the top of the tool. 

You can also use the tool to locate the map at a specified grid reference. To do so, type a grid reference into the area where the grid reference is normally displayed and click the locate button to the right of it.

Tip: Because all of the above functions are specifically of OS grid references, the CRS of the map view must be set to British National Grid (EPSG:27700), otherwise it will not work.

OSGR Tool button to drag a gridThe other function of this tool is to generate grids aligned to the British National Grid (or those for other CRS). To generate a grid, set the precision drop-down list at the top of the tool to indicate what size squares you want in the grid. Next engage the grid drag tool button (bottom left of the tool) and drag a rectangle on the map view over the area of interest.

OSGR Tool button to generate grid over polygonsThe tool button to the immediate right of this performs a very similar function except that it only generates grid squares that overlap a selected feature. So to use this, first select the feature(s) over which you wish to generate the squares and then click the button.

OSGR Tool label checkboxThe grid squares generated by this tool go into a temporary map layer called OSGR grid squares. An attribute (GridRef) stores the grid reference of each square. This can be used to label the layer in the normal way, but a quick shortcut to displaying this as a label is to check the label checkbox on the tool.

OSGR Tool user-specified grid optionInternational users! To generate grids based on CRSs other than British National Grid, you must select User specified from the drop-down precision list. With this option selected, you also need to specify a size for the grid. The dimension you specify should be in the units associated with the CRS - e.g. metres or degrees. Make sure you specify the size in the correct units otherwise the results will not be as you predict! For example, if you want to create a grid based on WGS84, you must first ensure that the projection of your map view is set to WGS84 (EPSG: 4326) and the grid size is set to something sensible such as 0.5. This will give you a grid of dimension 0.5 decimal degrees. 

OSGR Tool layer delete buttonYou can clear the temporary grid layer out quickly by clicking the delete button on the right of the tool. The tool is designed to let you generate these temporary grids extremely rapidly on the fly. But if you save a project with a temporary grid in, it won’t be there when you open the project again. So if you want to save a grid you have created, you will need to use the QGIS layer>save as function to save a copy of the layer to a permanent shapefile.

Video tutorials. (Videos may feature older versions of the plugin so the interface may appear different to the current release and operation may have changed.)

Youtube link
OSGR Tool: working with OS grid references

This demonstrates how to retrieve OS grid references in QGIS and how to re-position the map to a specific grid reference. Note that the video was made with an earlier version of the plugin so the interface may look a little different, but the basic process remains the same.

Youtube link
OSGR tool: generating OS grid squares

This demonstrates how to generate grid square features by dragging a square over the map or by selecting a map feature. Note that the video was made with an earlier version of the plugin so the interface may look a little different, but the basic process remains the same.

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