So I have been working on two mosaics in particular, the ones of Lake Dunstan from Cromwell to Luggate, and the ones of Clyde, over the past week but not as much as the previous week but that is what happens with ebb and flow of different time commitments etc.

The Lake Dunstan ones are complete. I am not going to show any more previews at the moment but just talk about the challenges as they have involved 72 current aerial photography layers from Linz in a matrix 8 wide and 9 high, plus three historical layers from Retrolens – a total of 75 layes. When you work out the numbers that is around 2,000,000,000 pixels which is a lot, and in the XCF file that is a 12 GB file. That is easily the largest GIMP project I have ever worked with, and very much tested the limits of my dedicated graphics computer with its 16 GB of RAM. When it came to rendering out the aerial maps for Qgis, they have been divided into six large tiles each of which consists of 12 of the original tiles (4 wide and 3 high) and these tiles are up to 200 MB each in size as a JPEG at 100 quality. The resource demands were such that I could only crop and render one of these six tiles at a time before Gimp ran out of resources and crashed (when the CPU, memory and swap meters were all maxed out) so I had to keep closing Gimp and reopening it to do the next tile. Qgis also has trouble handling them even on the map drawing computer with 32 GB of RAM and again I am seeing maxed out CPU, memory and swap and have had to put these images into a separate project just for this section. The next thing of course is to draw the map details and then produce the final images.

The main intention of this post as far as pictures go is to show the progress on Clyde. This image is from the Gimp project to re-mosaic the Clyde historic aerial imagery at a higher quality by scaling up the Linz layers to four times as many pixels so that we don’t have to scale down the historical images so drastically and lose so much of their high quality (mostly the NZR surveys which they intended to show a very high level of detail on the ground).

Part of the old station site with at far left the engine shed foundations (not sure when this closed) and towards the right hand side you have the turntable pit and one of the houses at this end of the station yard. The railway precinct at Clyde covered a significant area compared to some of the other stations, perhaps reflecting the fact that it was originally expected to be the railhead. There were at least two areas of housing in the yard and at least six houses of which several remain today, but there is no obvious trace of the turntable or engine shed foundations on aerial photography and a considerable amount of the station yard has been built over since the station closed in 1980.

I am still doing the rest of the mosaic which will cover up to 1991 when completed and I expect it will be completed today so that the map tiles can be produced and brought into the maps.