 Hello, this is Hans van der Kwas, senior lecturer at ICH Doft Institute for Water Education. In this video I'm going to show you how to make a beautiful visualization of the flow accumulation using ARIA lot, but first we need to do some pre-processing steps and we use QGIS and PC Raster. In another video I've explained how to enable the PC Raster scripts in QGIS on KONDA, so you can check it on this GitHub page, the link will also be in the description of this video. So I can activate the environment and then run QGIS from KONDA. And then QGIS starts and I've added four tiles from the SRTM, shuttle-rated topography mission and first I'm going to build a mosaic using a virtual raster. So I select here all the tiles, I don't want them to be stacked so I uncheck that box and then I save it to a virtual raster, call it DM Mosaic and there it is. I'm going to remove the other tiles, don't need them anymore and you see this question mark that means that we need to set the projection, so here it is in latitude-longitude. Now we need to clip it to approximately our catchment. I use a bounding box shapefile for that, you can also zoom in and use the coordinates of the canvas. I change the project to the projection of the bounding box because that's a projection I want to work with, UTM Zone 32 North and then I can use the export tool to export the DM Mosaic to a smaller version, call it DM Clip and I calculate the boundaries from the bounding box but I first have to set the projection, so it uses the UTM coordinates and then I can specify the horizontal and vertical resolution, I'll set it to 30 meters which is approximately the SRTM 1 arc second resolution. I specify the node data because there's some resampling taking place because the projection changes and there's the result, I remove the Mosaic and I also don't need the bounding box anymore, set the projection and there it is. And now I want to use this with the PC Raster tools, so I have to convert it to the PC Raster map format which is a GDAL supported format. So I go to these PC Raster scripts and there's convert to PC Raster format, it's a bit basic at the moment but it will serve for this purpose, in the future I will make it possible to choose different data types that PC Raster needs but now it will just simply create a scalar output, call it just DEM dot map, make sure you choose dot map and set the projection. The PC Raster doesn't store the projection anyways but this is just for our own reference. The next step is to calculate the flow direction in PC Raster terminology that's called the LDD, local drain direction and we use the LDD create tool for that. Here it is, the input is the DEM and basically it's the fill, sinks and flow direction in one and we keep all these parameters as default to fill it completely and we create the output that we will call flow direction in the PC Raster format. In the future also this algorithm will be improved so you can input spatials for those parameters but now it's just values. We change the projection, the flow direction map in the PC Raster format is different than from Saga, it has a different encoding of the compass direction, it uses the directions on your numeric pad on your keyboard. Now this is an input for the flow accumulation that we can calculate with the aquiflux tool where we need the LDD and a material layer but we don't have that yet so let's first create a material layer and here we will use the spatial function to create a map which just has value one in the scalar data type which means only one unit of material, unit of rain will then be put on every pixel and we use that to accumulate over the flow direction so basically we accumulate the numbers of pixels. There we go, it created the material layer which has just value of one for each pixel and now we can use the aquiflux tool, we choose the flow direction as LDD layer, we save the material and then we save the result to flow accumulation and we run the tool quite quick, there it is and you can imagine that it's quite a logarithmic scale for values with quite some extremes so we're going to style it in a proper way and go to the layer styling panel and here we use single bent gray because area law just needs from black to white where black is low and white is high so we can use the single bent gray but we need to change the stretching of the colors and because this is exponential we can use the cumulative count cut method and here you see the effect of that and you can play a bit with the figures there to get a better result stretching the colors. You'd also like to have some place reference therefore we use the geocoding plugin to find a place name here and this is close to Riemont, so I'm going to look for Riemont which is in the Netherlands and there it puts the point on the map and now if we want it really nicely in area lot we need to make it white because then it will really pop out of the scene so I'm going to make the label white and as you see it contains a bit more than the name of the city so I'm going to edit the attribute table and change it to Riemont the name of the city there it is now I want the placement a little bit better and I think also better to make it a bit bigger and in bold so it will really come out of the scene and now we also need to do something about a purple dot let's also make it white so it will pop out of the scene and remove the stroke and make it a bit bigger here it is so it will be quite prominent in the export so now we can export the result to a nice gray scale png file and we use the export tool and there we use everything that's in the map canvas extent and then we save it and the result can be opened in area lot area lot is a free tool to render these gray scale images into a 3d impression with shading it's open source and you can download it with a link that I'll put in the description let's open our png file that we just created and you see that it starts rendering it immediately it takes black as low and white as high and the blue bar shows how far the rendering is and you see the result improving and it gets sharper now there's a lot of things you can play with so it's just a matter of playing around to get the right result you can change the way of visualization and the exaggeration put it a bit less here you see the effect now and it just every time you change something it starts rendering again you can change the position of the sun the color of the background and yeah just try what's there to make a nice result and with your mouse you can rotate the scene and zoom in and out and then finally you can save your result with a little camera button on the bottom to a png file that you can post somewhere so enjoy and hope to see some nice creative results so this works with any gray scale image that you have just think about that black is low and white is high enjoy