Loading raster data

The guides below detail how to load raster data for the following products:

QGIS

It is assumed that the user will have already set the default co-ordinate reference system in QGIS to British National Grid (EPSG 27700). Instructions of how to do this can be found in the QGIS Getting Started Guide;

Loading and Displaying GeoTIFF supply

Open QGIS. Select ‘open raster layer’ from the left hand toolbar.

In the next window, click ‘browse’ and navigate to the folder where the OS OpenMap-Local GeoTIFF files are located.

Select one or several GeoTIFF files as required. Once selected, click ‘open’.

The files will then appear in the QGIS map window.

Zoom to the desired map scale using the zoom buttons or set the scale using the drop-down option at the bottom of the window. It is recommended to set the viewing scale to 1:5000 or slightly less.

As an alternative to loading the GeoTIFF files one at a time or in groups, it can be quicker and easier to create a virtual raster table (VRT) to load the data.

In the QGIS main menu, select ‘Raster’ and then in the drop-down menu select ‘build virtual raster (catalog)’. In the resulting window, the user has the option of selecting a folder containing all the raster GeoTIFF files, or the user can simply select several files with which to build the virtual raster table.

It is highly recommended, for OS OpenMap-Local, to keep the maximum size of the VRT file to a 100km2 grid square, for example, SU. In some cases, the maximum number of tiles will be smaller than this.

The user also has the option of loading the virtual raster table when finished. Once the choice is made click ‘select’ and then navigate to the selected folder.

It is then necessary to specify the name and location of an output VRT file. It is normal procedure to place the VRT file in the same folders as the GeoTIFF files.

Once the user is happy with the name of the VRT file and its location, click ‘Save’.

The dialog box is now populated with the data required to construct the VRT file.

When satisfied, click ‘OK’. The process should now start and run to completion. It is important to note that in testing with the beta release data, the actual maximum number of OML raster tiles that could be included in a VRT file was considerably less than a 100km2 grid tile, as indicated previously in this guide. This is because there are 400 separate GeoTIFF files within a 100km2 tile and the actual size of the GeoTIFF file does vary according to the density of detail in the area which it covers. The user must experiment with their own system to find the optimal number of tiles for a VRT table.

The user can now click ‘OK’ twice and then close the Build Virtual Raster catalog dialog box.

The OS OpenMap-Local raster data should display in a similar fashion to the example below, if the ‘load data into canvass when finished’ option was ticked in the building dialog window. If this option was not selected, the VRT file will have to be loaded manually by selecting the load raster data button as described previously and then selecting the .VRT file just constructed. For best viewing results, set the viewing scale to 1:5000 or slightly less.

ArcGIS ArcMap Desktop

For the purposes of this guide, it is assumed that the user is familiar with the procedure of creating a file geodatabase within ESRI ArcGIS. A file geodatabase is used to contain a raster catalog. The procedure for creating a raster catalog will be described later. The construction of a file geodatabase is described in the loading of the vector version of OS OpenMap-Local section of this guide.

Loading and Displaying GeoTIFF supply

Open ArcMap. To load the GeoTIFF file on an individual basis, or in small groups, click ‘Add Data’.

In the dialog box, browse to the folder where the GeoTIFF files are to be found. If the folder is not in the list of connected folders, the user will have to create a new folder connection to it in the usual way. Select the GeoTIFF files required and click ‘Add’.

In the next dialog box, the user should consider whether or not pyramids should be created before loading the raster data. In this case we are not going to create pyramids with the data.

Click ‘no’ on this dialog box. This must be repeated for all the raster files selected to be loaded. The data loaded should appear in a similar fashion to what is displayed in the next example. Select a suitable scale for viewing the data, probably around 1:5000 or less.

The best way of loading multiple raster files in ESRI ArcMap is to use a raster catalog to store the data. This method works from within a file geodatabase, which can also be used to store the vector version of OS OpenMap-Local if required. Details of how to create a file geodatabase in ArcCatalog are described in the loading of the vector version section later in this guide.

Assuming the user has a file geodatabase already created to hold the data, the following procedure can be used to create a raster catalog to hold the raster files.

Open ArcCatalog. Right-click on the file geodatabase that has been created to fold the data and select ‘New’ ‘Raster Catalog’.

In the resulting dialog box, the user must give the raster catalog a name. In this box one can also specify a co-ordinate reference system and if the catalog will be managed or unmanaged. A managed catalog will physically contain all the raster tiles, and will take longer to create. However, if the file geodatabase is to be shared, the data will be available with the database and can be shared more easily with other users. In the example we have created a managed catalog with the British National Grid co-ordinate reference system. Click ‘OK’ when finished.

Once the catalog has been created it will appear as an entity within the file geodatabase. Refresh in ArcCatalog to see if it has been created. To load the raster files into the catalog, right-click the raster catalog and select ‘load raster datasets’.

Browse, in the next dialog box, to the folder where the raster datasets are stored and select the ones required for use. Click ‘OK’ when finished. The list of selected raster will now appear in the dialog box.

The output geodatabase will normally be the correct one where the raster catalog is located, so the user can then click ‘OK’. This process may take some time if there are many files to be loaded to the catalog, and the catalog which is being used is of the managed type. Once completed, the user will see the list of files in the catalog listed in the view pane of the main ArcCatalog window.

In ArcMap, select ‘Add Data’ and then browse to the file geodatabase where the raster catalog is stored. Select the raster catalog and then click ‘Add’. The data will now appear in the ArcMap main map window.

Select the raster catalog and then click ‘Add’. The data will now appear in the ArcMap main map window.

If a grid similar to what is shown in the example below is seen, it means that the catalog contains over the maximum number of raster tiles set to be displayed in ArcMap, which then defaults to a wireframe grid.

If this happens, the wireframe mode should be turned off. Right-click on the raster catalog in the table of contents window, select ‘Properties’ and then select the ‘Display’ tab. Click on the ‘Never show Wireframe’ radio button. Then click ‘OK’ or ‘Apply’. The raster data should now display correctly.

MapInfo Professional

For the purposes of this guide, it is assumed that the user is familiar with using MapInfo Professional and knows how to perform certain functions required to handle raster data. MapInfo Professional 64bit version 15.2.4 is being used in these examples. Users of the 32-bit version of MapInfo or those using earlier releases will see different screens to those shown here.

To open the GeoTIFF raster files, select Open Table either from the ribbon button list at the top of the screen or select the ‘Home’ tab and select the table option.

In the next window, navigate to the folder in which the raster files are found. Initially, on a first load, the user will need to change the files of type to raster image from the default ‘tab’ type.

Select the number of raster tiles required and then click ‘open’. The raster data is now displayed in the map window.

MapInfo has loaded each of the raster tiles individually. Although this is normally OK for a small number of tiles, when working with large numbers of raster tiles and/or multiple layers of data, it is more efficient to create a seamless table in MapInfo to hold the data.

The user will need to load the seamless table manager under the Tools button in the Home tab of MapInfo Professional.

The user must load at least one raster tile into the map window to start the process of creating a seamless table. Once this is done, double click seamless manager in the tools drop-down as shown above. The following window will appear.

Click ‘New Seamless Table’. Then select a folder in which to store the seamless table and give the table a name. Then click ‘Save’

MapInfo has now created a seamless table containing the one table that was loaded in the map window. The user can now add additional tables to the seamless table by appending additional tables to the one just created. This procedure works differently to the process used in earlier 32-bit versions of MapInfo. In MapInfo 64-bit, all the tables to be appended need to be loaded into the map window first.

This time click the ‘Append to Seamless Table’ Option. The browse window will appear.

Select the seamless table to be appended. In the example above it is ‘OML.TAB’. Click ‘open’. The following message will appear depending on the number of tables loaded into the map window.

From now on, the user can load all eight tables (in this example) at once simply by loading the seamless table. It is also important to note that the seamless manager will only work on tables created by MapInfo when loading in the original raster files. It will not work with GeoTIFF files directly.

CadCorp Map Modeller