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Hi everybody.

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Welcome to the second tutorial
on Google Earth Engine.

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This tutorial is gonna help you complete

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your Yellow Dig assignment for the week.

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So, if you wanna look at
the Yellow Dig prompt,

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before watching this video,
that might be helpful.

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I'm gonna teach you in this
tutorial how to draw an ROI

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or a region of interest,

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and then how to pull up
some very basic imagery

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to go into that ROI.

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So, in order to draw ROIs
in Google Earth Engine,

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there is a way to code,

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how to code with
coordinates your geometry,

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but it's easier to use
these functions down here.

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So, as I showed last week,

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we have this hand function
that helps us move around,

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but we also have these
other geometry buttons.

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So for example, if we
wanted a point feature,

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we could drop a point

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and that's created a
geometry with our point.

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I'm going to delete that,

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because I don't wanna point right now.

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We can also draw lines or polygons

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or this is a rectangle.

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Today I'm gonna draw a polygon

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and I'm gonna put my ROI as Fort Collins,

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since that's where I live.

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You should use an ROI
that might not be the ROI

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that you wanna do your final project on,

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but a location that is
of of interest to you.

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Okay, so I'm gonna click
on this little polygon icon

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and now I can start drawing.

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So, I'm just gonna click
around Fort Collins.

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I can do as many dots as I want

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and once I click back on that first dot,

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it'll complete my polygon.

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We can also,

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if you want to look at the satellite,

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you can do that.

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I'm gonna keep it on the map for now.

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So, when you've drawn a geometry,

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if you wanna change some elements

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of the geometry immediately,

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you can change its name.

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So, Fort Collins, you could do that.

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You can also change it from a geometry

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to a feature or a feature collection.

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A geometry just has
coordinate information.

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A feature can also have properties.

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So, if you want, you can
add some more data to it.

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For now,

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I'm just gonna keep my Fort
Collins geometry as a geometry.

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So I'm gonna say, okay,

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and you might notice that
up in my script editor,

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a variable has been added at the top.

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So, it's taken this geometry down here

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and include it as a variable here.

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So, now it's ready for
me to do analyses on.

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Okay, I'm actually gonna turn
off the geometry down here,

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because I kind of find the geometry

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to be distracting sometimes.

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You'll see if we visualize imagery,

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the geometry always sits
on top of the imagery

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and I don't want the imagery
to be sort of shaded red.

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I wanna be able to see it in full.

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So, I'm gonna turn this off,

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but it still exists, it's still in there.

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And by the way,

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if we wanted to see the coordinates,

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we could go in here and see
each one of those points

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that I drew.

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We could see the the lat and
long coordinates for that.

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Great.

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So, I'm gonna start by
importing some imagery,

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some Landsat imagery.

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If you remember, we talked
about Lansat imagery last week,

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and I'm gonna use Landsat Eight.

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So, I believe Landsat four
through nine are in here.

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Yeah, so that it doesn't seem
like they have Landsat Threes,

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but four through nine are in here.

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I'm gonna use Landsat Eight.

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You're welcome to use
another one if you want.

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I'm gonna use the top of
atmosphere reflectance.

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You don't want the raw scenes,

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those are unprocessed.

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So, top of atmosphere, TOA reflectance,

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and I'm just gonna say Import.

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And now it's imported into my script.

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We can rename it by clicking on it.

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I'm gonna rename it L8, for Landsat Eight.

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Another cool thing is
that you can click on

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this blue name of the dataset

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and a little box pops up and it can,

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it tells you information
about that dataset.

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So, for example, the dataset
is from 2013 to the present.

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There's more description here.

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If you click on these tabs,

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it tells you other information,

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like it tells you the band names

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and what they are describing.

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So, the important information
here might be that

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the red band is band four,

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green is B3

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and blue is B2.

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So, that'll be helpful

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when we wanna make a true color image.

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We can see some image properties.

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So, it has some information
about cloud cover.

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We'll get into that more next week.

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And then it has some terms of use,

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including how you might cite
or acknowledge this data.

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Okay, so great.

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I'm gonna click Close

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and I'm gonna start processing
this Landsat Eight imagery.

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So, I'm gonna create a variable
called Landsat Eight image.

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So right now, if you see,

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this is an image collection.

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So, this L8 variable
includes every single tile

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of Landsat Eight that is available.

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I don't want all those tiles,

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that's way too much information.

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So, I'm gonna start filtering
this image collection down,

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so that it's just a single image.

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And the way that I do that is
I'm gonna create a variable.

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I'm going to put L8 dot,

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and then I'm gonna filter it.

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So, first I'm gonna filter it by bounds.

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So, that basically means that I only want

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the imagery that is touching my geometry.

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So, I've said dot filter bounds.

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And then within these parentheses,

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I've put the name of my ROI,

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so Fort Collins.

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So, if I left it right here,

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that would basically give
me a new image collection

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that is much reduced.

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That only is imagery, again,
touching Fort Collins,

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but that's still an
image collection, right?

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So, if we want just an image,

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we need to filter it down even more.

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And there's a variety of
ways that you can do that.

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One of those ways is you can
just get the first image,

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within that image collection.

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And you would do that by saying dot first.

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Another way is you can get
the median of those images.

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You can go crazy as well.

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You can get the max of
all of those images.

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That won't look very
good, but you can do it.

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I'm gonna start off by just
getting the first image,

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within that image collection

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and then I'm gonna show
you how to visualize that.

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So, the function to visualize anything

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in Google Earth Engine
is called map add layer,

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and then parentheses after that.

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There's a variety of arguments

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that go within this map add layer.

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Again, if we want to know all
of those different arguments,

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we can go into the docs

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and look at this function map add layer.

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And let me just,

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map, add layer, there you go.

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So, if I click on this,

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it shows the different
arguments that are helpful.

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So, the argument that is
not italicized is required

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and the arguments that are
italicized are optional.

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So, you need an object to visualize.

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And then an optional argument
is the visual parameters.

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Another optional argument is the name,

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the shown, the opacity.

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And you can see what each of
those things mean down here.

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So, the image or the object

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that I am visualizing is the
L8 underscore image variable.

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And I'm going to leave

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the visualization
parameters blank right now,

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but it within these curly parentheses

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is where they would go.

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And then inside the quotation marks,

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I'm just gonna name it,

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I'm gonna say, this is
my Landsat Eight image,

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and I'm gonna run that.

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It might not look very good,

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but I'm gonna run it
just to see what happens.

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All right, so what we're
looking at right now

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is an entire tile of Landsat imagery.

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If I want just my Fort Collins geometry.

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So, remember we made that geometry.

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It's much, much smaller
than this tile, right?

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So, if I want the imagery
just to fall within that tile,

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I'm gonna use the function called clip.

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I'm gonna put Fort Collins in there.

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So, I'm gonna run that again.

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And now the imagery is just
within this Fort Collins ROI

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that I made.

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This still doesn't look great

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and there's a few things
that we can do to help it.

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So, I'm gonna use the inspector tool

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and click on the imagery and
I'm gonna see what's going on.

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So, let's see if I click this.

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There you go.

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So, it shows the reflectance values.

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The pixel that I clicked,

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it shows the reflectance
values for all of the bands.

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So, this gives us some good
information about what the range

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of those bands might be.

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So, within the visualization parameters,

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some things that we can input
here are the min and the max.

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So, it's pretty clear that
the max values are pretty low.

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I'm gonna say the max is about 0.02.

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And then also,

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I'm not really sure what
it's visualizing here.

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We can go into the layer and
click this little settings

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and see what it's doing.

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So, it is doing a three
band visualization right now

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with band one, band two and band three.

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But if you remember in Landsat Eight,

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the red, green, blue is bands,

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bands four, three, and two.

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So, red, green, blue,

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red is band four,

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green is band three,

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and blue is band two.

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So, I'm gonna put bands in here.

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And when you have lists
in Google Earth Engine,

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you have to put them in brackets.

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So, I'm gonna make my
list of the three bands

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that I'm gonna visualize.

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Band four, band three, band two.

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And then I have my min and my max.

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So, I'm gonna run that again.

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Okay, that looks better.

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I can see some things
in the landscape now.

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And the min and the max also helped a bit.

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There's some clouds here.

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I'm not gonna worry about that right now.

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But next week I'll show you
how to get rid of clouds.

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I'm gonna now show what happens
if I use some different ways

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of summarizing my image
collection into an image.

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So, rather than using first,

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what if I use median?

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What does that look like?

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And it's gonna take a bit longer,

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because it has to get the median,

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over all of those different images.

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So, it's a little bit slow.

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So, if you run this on your computer

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and median takes forever, that's okay.

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Maybe just use first for now.

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Okay, the image is kind of washed out,

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so if I did median,

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I might wanna change my min
and my max a little bit.

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Just for fuzzies, let's
see what max looks like.

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It's probably gonna look very white.

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It's probably gonna take the image

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that has like the most clouds.

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Yep,

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because clouds have a really
high reflectance value,

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remember?

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So, when I put max here,

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it's basically taking,

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all of the pixels within
this huge image collection

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that have the absolute
max reflectance values

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and combining those into an image.

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So, not the most intuitive
or interpretable image ever.

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I'm gonna also show mosaic.

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I think the book uses mosaic a lot.

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And I believe what mosaic does is,

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oh,

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yeah, interesting.

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So, mosaic is also giving me
pretty high reflectance values.

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But mosaic is helpful

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if you have, for example, your ROI

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is in between two different tiles,

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then it'll help join those tiles.

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But honestly, median is,

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it does the same thing.

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Median also mosaics tiles.

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So, the two functions that
I use the most are median

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and first.

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Great, so this is all that you need to do

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for Yellow Dig this week is draw your ROI

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and then just visualize
some data within it.

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You can use Landsat Eight.

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You're also welcome to challenge yourself

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and use Landsat Nine or
Seven or Five instead.

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An important part of coding,

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save your work.

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So, click Save

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and then I'm gonna not save it.

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And then don't forget to get the link

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by clicking this button and
then copy paste this URL.

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All right.