Since our last blog post some three weeks ago, the focus has been on creating various volumes with the intention of these being uploaded on the Volumes site. Work has been going on for Volume 10, as well as parts of Volume 11, the most notable latter example being the maps which have been created for the Dunback and Makareao Branch lines.
Whilst the intention is to get the Volumes site working as quickly as possible (and we see this being implemented in some form in the coming week), Volumes content has also been important. The most important development has been a redesign of the template for producing the individual map images which has been trialled in the Dunback-Makareao maps and is now being deployed to all subsequent volumes, at the time of writing for the updated section of the Main North Line’s Picton Section. The change principally incorporates a field to display a unique filename, the actual text of which is based upon the distance in kilometres of the covered section. The changed filename system is important – previous filenames were based on a linear sequence of the volumes commencing from the point of origin – because in the recent updates of the existing Main North Line content the existing volumes images had to be renumbered numerous times as new images were added to the volume.
By creating a filename based on the absolute location (distance) instead of a sequence number, the filename for a particular location can be unique and so it becomes possible to create the volume images out of order, without having to have created the rest of the volume from the beginning first. This greatly facilitates updating selected areas of content at a later time without having to use a script to change existing filenames as was done quite recently in Volume 10 (Main North Line). Having the filename displayed on the map itself is important because it makes it possible in the case of some maps that use historical aerial photos, to ensure there is some identifying information displayed on the map to show what location it is of. It is also relevant as the last four characters of the filename indicate the year depicted which in the case of historical aerial photo layers finally provides an automated capability to display this information about the age of the aerial photo(s) used in the image.
In the last few days a script has been written to further automate and speed up the task of volume image creation. This is accomplished by making use of the Qgis Python scripting capability to select the layers which are being included as the background of a map automatically as soon as the filename for the volume image has been specified. In other words there are just a handful of steps to create a volume image: set up the map in the Qgis layout template that controls the exact view, specify the filename to be used and then run the script, which automatically selects the layers to make up the image and then exports it from the layout to a file. By automating the layer selection, this balances the extra work needed to choose and enter a filename for each map image. All volumes produced henceforth will use the new system and eventually the few existing volumes which precede it will be updated to it.
As the new content has been added to the Dunback and Makareao Branch maps recently the Webmaps will need to be updated for this area and also for the Picton Section maps, however the maps of the full Picton Section have not yet been completed; it is mostly the historical aerial mosaics of this section which are almost ready for use but from which maps still have to be drawn in a number of areas. Volume image creation is therefore focusing on the areas which were recently updated as part of the Picton Section maps e.g. Wharanui-Ward, south and north ends of Seddon (not the township itself), Wairau Bridge-Para and Elevation. The rest of the Picton Section volume images will be updated to the current standard of design and content as the maps for each part of the Picton Section are finalised.