Map Algebra and Math 1

Python for Spatial Analysis in ArcGIS Advanced Python in ArcGIS for Spatial Analysis
10 minutes
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Today we will learn how to conduct sale by sale calculations. There are two ways one is using the visual analyst tools. Another way is to use the raster calculator. Let's see what's in the raster calculator. Well a raster calculator is under map algebra. It basically it builds and executes a single map out your box expressing using Python thing text in a calculator like interface is conditional tools.

Can gang comb pick that now has caught cause corresponding tools and its mass to has courage pounding And there's more functions on the functions in the raster calculator like this one has corresponding tools in the toolbox. Basically this interface contains everything I need to just make the calculation can be written more easily during example, I have already added em raster data as open the raster calculator and choose this raster data and I just add a value of 100 to this data. Here is the final result. This is the mean tech the value you can already actually see range of value, the maximum and the minimum already 100 larger. This will mean to see what the values change for one. So let's use the identify button and choose the layer to be visible layers.

So when we pick one sale, both layer value will show. again see for this sell, the new map value is 100 a larger than before. Let's open a raster calculator again, let's just do our more complicated a calculation this time. Let's just say is the layer times 1.25 and then plus a number. Maybe make it more complicated. I'm just gonna randomly put something using a brand kit.

Just make this formula a little bit more comprehensive. It doesn't really have any meaning here. Okay, let's finish this equation and our one. Here is the result. This check the value again. See, the value changes, we call the function is 1.5 times the input plus one point is three times two.

Another kind of calculation is by judging whether or not a equation is true or false. If it's true value is what if it's false, the value is zero. Besides the right corrector formula, there's another thing very important, which is the environment for doing this calculation. Let's just go through the environment first. Really quick. There are all those environment attacking nations here, you can change.

And currently I'm just showing the default for the environment setting of all the settings. The raster analyst setting is the most important one. Okay, now let's get it ready to use to to, to use the Python script for the two as Steve was saying the tool There are environmental settings as well in the tag raster analyst. So you can peek one from the existing layer or make a definition for the cell size over itself. And a mask. mask basically means the region, you want it to conduct that calculation.

You don't need to calculate the whole dataset, you can actually just draw a region or import a feature layer which covers the region where you want to conduct the calculation. Environment The setting is optional, but they're helpful. Okay, let's go model builder and export it the Python syntax for this tool Let's add the tool here and a few the tool by click on it. Let's just use those layer as an example. Okay, we have our first go to already, let's add another two minus two. Let's put a parameter for this too as well.

Let's just use our random layer as the example that's used to output the first calculation as the input and the truth another layer for the other input. Okay, now let's get the environmental settings to survive. counted to go to variables environment. raster analyst. There are two things we can change for the environment attachment one cell size. Another one is Mac.

Let's get the cell size first. Currently the default setting for cell size maximum of all the input layers and other environmental settings we can do for the raster analyst is the mass. We can choose the mask from the existing layer we have used it to to align the cells the output layer now the model builder is finished. Let's export to Python script Okay, so this is a Python script for the model we just viewed, has changed it so it doesn't have the redundancy. There's our nother way of using this model builder is using the layers we actually use the constant values to create a raster ourself. It's very easy.

Let's just go back to the model builder. change to the layer two is constant value. Now the model builder is finished. Let's export to Python script Make sure all the blanks are filled with a pyramid. Now let's export the model builder into a Python script open. So now you can see the code still has some redundancy.

Let's just modify it really quick. This is a Python redundancy. If you know Python language, then this is very easy to understand. Instead of pass the variable two times you can actually just say this way. Okay. Next To cast this to our real practice using the code in our tools that we have learned from the class.

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