Category: NZTekonverse -> Qgis

NZ Rail Maps: Using Gimp To Georeference Retrolens Aerial Photos [4]: Getting Started With Overlaying

So now we can look at how we actually do the georeferencing. This happens as a multi part process, and explaining the steps gives you an understanding of how it all works. The basic of georeferencing a historic aerial photo, is that by aligning it to a current aerial photo, of which we know the…

2020-05-24
NZ Rail Maps: Using Gimp To Georeference Retrolens Aerial Photos [3]: Getting Imagery Into Gimp

So let’s get this rolling. First thing I need is to download the layers from Linz Data Service. Which in this case is at the following URL: https://data.linz.govt.nz/layer/53399-northland-01m-urban-aerial-photos-2014-2015/ The layer is called Northland 0.1m Urban Aerial Photos (2014-2015) and covers the stations of Whangarei, Portland and Kamo. It also covers the port area of Whangarei,…

2020-05-23
NZ Rail Maps: Using Gimp To Georeference Retrolens Aerial Photos [2]: Preliminary Considerations

So I aim to write one post every day about this topic (this post was supposed to be finished last evening but has stretched through until this morning) until all the parts are completed, there are probably three or four parts. This is easy because I am doing georeferencing at the moment on a particular…

2020-05-23
NZ Rail Maps: Using Gimp To Georeference Retrolens Aerial Photos [1]: Introduction

OK so here is another post in the NZ Rail Maps category and this post will explain how I carry out the georeferencing of the historical Retrolens aerial photos to produce the maps for the NZ Rail Maps project. This is a very rewarding aspect of the project but it does take a lot of…

2020-05-21
NZ Rail Maps Technical Review 2020-04-18

So we are now at Qgis version 3.10.4 for the NZ Rail Maps map production task. Back a way we had a lot of trouble with Qgis with WMTS layers which were unusable at that time. Since then however we haven’t been able to replicate the problem but we suspect that their code has bugs…

2020-04-18
NZ Rail Maps: Large Area Raster Tiles At Reduced Quality Setting

Using Qgis to draw the maps, we’ve run against a few times some sort of limitation on the number of raster layers that it seems to have, which runs out a long time before hitting the actual resource limits of the computer it’s running on. This in turn limits the number of raster layers that…

2019-11-18
NZ Rail Maps: Optimising Gimp and using 4x4x4 grid for mosaics [4]

Last time I posted I wrote about my experiments rescaling layers in Gimp from 0.4 metres to 0.2 metres pixel spacing and 0.3 to 0.15 metres pixel spacing and seeing how these matched with the NZR station surveys. I am still in two minds about whether to go with 0.2 metres from 0.4 metres source…

2019-05-18
NZ Rail Maps: Optimising Gimp and using 4x4x4 grid for mosaics [3]

Since last writing on this subject I have further determined that I can scale 0.3 and 0.4 metre pixel resolution background Linz aerial images to double the scale (0.15 and 0.2 metres) and these scales work very well with the 1:4300/4325, 1:5500 and 1:8000 scale Retrolens aerial photos which are the best ones for creating…

2019-05-08
NZ Rail Maps: Optimising Gimp and using 4x4x4 grid for mosaics [2]

In the previous post in this section I wrote at some length about the use of grid segmentation of Linz base layers that were at resolutions of 0.3 to 0.4 metres pixel size. The grid segmentation being used to rescale these layers to 0.1 metre pixel size and then the original grid references were assigned…

2019-05-01
NZ Rail Maps: Scaling up map mosaics & creating new tile grids

One of the issues that comes up with doing the map mosaics for NZ Rail Maps is that the resolution of Retrolens aerial imagery can often be very high, when using the official NZR survey images at the scale that they appear on Retrolens. A typical scale is only 1:4300 which gives us a lot…

2019-02-09