Today we had our second GIS-meeting online. Attendance was still limited, but at least we have found a rhythm now. Today's meeting was short but informative.
Extracting islands from DEM
We discussed the May topic at length, which could not be covered last time. The solution is posted under the original question.
Raster reprojection in QGIS
Fabian asked an intriguing question. As most QGIS users know, there are at least two ways to reproject a raster layer in QGIS.
1) 'Raster > Projection > Warp' using this tool you can reproject a raster file to a new CRS and save it to a new file.
2) 'Export > Save as' when saving a layer you can assign a new CRS.
You can also use other external tools from GRASS or SAGA to reproject. However, when comparing the results of these ways, you will see that the reprojection results are slightly different. This effect is known in the community (https://gis.stackexchange.com/questions/214757/raster-reprojection-in-qgis-leads-to-different-results), but there appears to be no detailed explanation so far. Apparently the different ways use different tools for the reprojection. We do not know, which one gives the best results. Further research (e.g. QGIS-User-List) would be useful.
Ideas for next meetings
Fabian explained his troubles to connect GRASS 7 with R. He will prepare a little presentation on that topic for the next meeting. We decided to dedicate the next meeting to interfaces of GIS to other software packages.
Martin asked for an introduction to spatial network analyses. This will be our topic for the august meeting. We will prepare a data set and Benjamin agreed on a little intro to that topic. Benjamin also showed us the GAMA-Project, which is an open source software for agent based spatial modelling (https://gama-platform.github.io/wiki/Home). This tool can also be used for network analyses.
High quality test and open data sets are available for free from the Mexican governmental surveying office (https://www.inegi.org.mx/datos/). The problem is, that so far non of us has any archaeological data to combine with these.
