Hydrological processing with python script

Python for Spatial Analysis in ArcGIS Advanced Python in ArcGIS for Spatial Analysis
10 minutes
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In class to learn the hydrological tools under Spatial Analyst to create a flow direction accumulation. Last class we learn the basic tools to create a basis from flow directions. In this class, I will introduce you our new tool which is called watershed. Okay, that's the recall over Python script. In class two, we link the flow direction, flow accumulation and conditional to make the streams the main class seven, we added the base into after the flow direction. This class let me show you the difference between watershed and paste into under hydrological tools is special To listen to what is the difference between basing and ownership.

Let's do an example first. So I have already prepared the field a DM from the SOS dm, the flow direction from the DM and the flow accumulation from the flow direction. Now let's do a base thing first. Add the flow direction as the input. And then here is the result. You can see there are many different colored regions in this map.

That means they're different facings need to have a better visualization effect we can use conversion from raster to polygon tools. This tool will help us to create polygons from a raster file. Okay so now, this the polygon we created for the base things. This try watershed tool. The input is the flow direction and it has another input which is support data. You can basically define your own pour data from the flow accumulation layer needed to define your data on the river.

So we need to zoom into the river. lighter colored one is the river. Practice, I have already created a poll data that's added the poll point data and to make it more visible it changes. Okay, so the green.is the poor point it's checking if it's on the river. See, it's actually landed on the river line. But what if it's not?

Let me introduce you the editing tool. editor, start editing truth layer we want to add it, which is a poor point. When that when that error change like this, you can move the points anywhere you want. Just move it back to the river and stop editing and escape at it. Now, we have all the input layers ready. That's to try to create a Watership using the watershed tool.

Input flow direction, the pool point and that's over output. To make it more clear, we can convert it to polygon. See, this is a difference. The watershed is on The light colored polygon, the basics are the blue colored ones. Let's compare watershed is only a small segment of the painting while basins use the edge of the sauce, the sauce flow direction as the outlet, the wondershare that you support point as the outlet. So, there are many things, but there is only one watershed using this one pole point and that the upstream parts aligned only the downstream part due to a different outlet.

Why is larger one is smaller. Now, let's talk about two important things of raster data. One is the resolution of raster data. I have prepared to use three sets of Digital Elevation Model data for the same region 400 meter resolution 19 meter resolution and a 30 meter resolution. I prepared the surface the DTM under the hillshade. So, it will give you a better visualization.

If I uncheck the hillshade the map will look more like flat with handshape it give us a like a three D effect. So, let's just check the hillshade as well. From the current zoom window, you cannot really feel the difference between different the resolution and less looming that's how 450 meter resolution dm look like. That's how 90 meter resolution that half 30 meter looks like. As you can see with find a resolution, the map will contain more details and the finer resolution the end will also take up more memories. So there is a balance between resolution of the region the DM is covering how detailed you want the map to be, there's a balance.

The good thing is the ArcGIS can't allow us to resemble over data to make sure we can have different resolution. The resemble data is under data management tool raster raster processing, please sample input is our range of data set. The output is the resemble the data set, we can pick up the resolution by the existing layers we have added or define the resolution. Let's talk about the second most important coordinate system. This is the current projection system, we can right click layer tech property. Coggan data system.

The current system is WGS 84 has to change the new projections this I'm going to see how the map will look like. has changed a different one that's changed a protected system. The map now looks different. The shape is stretched The wider now let's change another projection system to make it a more clear shape of the map is just tort because we use the different the projected system. However the projection is the sum is only changes in our way we look at it to change in the data projection, make sure each data is actually projected in the new projection system, we need to use a tool. The tour is under data management, projection, transformation, raster projector raster.

Input is the data arranged in our data and the output is the projected data We want to introduce the projection system here from the geographic coordinate system from the projected coordinate system, all from the layer coordinate system, the layer where the layers has been added into the workspace. Understand that a resolution of raster data and projection system of raster data is the whiteout for us to conduct spatial calculation between raster layers in our future classes.

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