Hillshade

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En provenance du cours de University of California, Davis

Imagery, Automation, and Applications

369 notes

University of California, Davis

Imagery, Automation, and Applications

369 notes

Cours 4 sur 5 dans Specialization Geographic Information Systems (GIS)

Welcome to the last course of the specialization (unless your continuing on to the capstone project, of course!). Using the knowledge you’ve learned about ArcGIS, complete technical tasks such raster calculations and suitability analysis. In this class you will become comfortable with spatial analysis and applications within GIS during four week-long modules: Week 1: You'll learn all about remotely sensed and satellite imagery, and be introduced to the electromagnetic spectrum. At the end of this week, you'll be able to find and download satellite imagery online and use it for two common types of analysis: NDVI and trained classification. Week 2: You'll learn how to use ModelBuilder to create large processing workflows that use parameters, preconditions, variables, and a new set of tools. We'll also explore a few topics that we don't really have time to discuss in detail, but might whet your appetite for future learning in other avenues: geocoding, time-enabled data, spatial statistics, and ArcGIS Pro. Week 3: In week three, we'll make and use digital elevation models using some new, specific tools such as the cut fill tool, hillshades, viewsheds and more. We'll also go through a few common algorithms including a very important one: the suitability analysis. Week 4: We'll begin the final week by talking about a few spatial analyst tools we haven't yet touched on in the specialization: Region Group to make our own zones, Focal Statistics to smooth a hillshade, Reclassify to change values, and Point Density to create a density surface. Finally, we'll wrap up by talking about a few more things that you might want to explore more as you start working on learning about GIS topics on your own. Take Geospatial and Environmental Analysis as a standalone course or as part of the Geographic Information Systems (GIS) Specialization. You should have equivalent experience to completing the first, second, and third courses in this specialization, "Fundamentals of GIS," "GIS Data Formats, Design, and Quality", and "Geospatial and Environmental Analysis," respectively, before taking this course. By completing the fourth class you will gain the skills needed to succeed in the Specialization capstone.

À partir de la leçon

Digital Elevation Models and Common Algorithms

In this module, we'll be looking at DEMs and workflows. In the first half, we'll make and use a handful of products derived from digital elevation models, including contour lines, hillshades, viewsheds, and the cut fill tool. In the second half of the module, we'll go through a few common algorithms, starting with one of the most important ones to know: the suitability analysis. Then, we'll learn about the hydrologic processing you did in the tutorial assignment for the previous module and go through it step by step together.

Module 3 Overview0:36

Rencontrer les enseignants

Nick Santos
Geospatial Applications Researcher
Center for Watershed Sciences

[MUSIC]

Hello everyone and welcome back.

In this video I'm going to show you a bit about making a hillshade from a digital

elevation model.

This is something we've done informally in the videos and then more explicitly in

assignments in previous courses, but I want to show you a few tips and

techniques that maybe we didn't cover in those previous hillshades.

So first, we have our trusty digital elevation model here for

the Navarro River watershed.

And creating a basic hillshade is actually a pretty simple thing.

And if I go to Spatial Analyst Tools and

then I go to the Surface tool set, I can run the Hillshade tool.

And I can set the input raster and

output location, which I'll call navarro_hillshade.

And I can set basically the sun angle, which angle is on on the compass.

And how high above the horizon it is for

how it will handle the shadows in the hillshade.

And if I wanted to maybe do a low sun angle model,

maybe if I wanted to try 15 degrees above the horizon model, I might do model

shadows so that it can have shadows cast across the landscape by larger features.

So, let's first take a look at what that ends up being when we run it.

In the meantime, we'll set up another hillshade, Which

we'll call navarro_hillshade_normal,

or maybe, 45, for the altitude.

And I want model shadows, and I'll just keep the altitude standard.

And let's see what that looks like.

So here's this one, where you can sort of see shadows

keeping across the canyon here from these taller features.

Whereas in this other more normal more typical hillshade,

what we really just have is

enough of the shadow to show you what the features on the landscape look like here.

So, with shadows we're getting these deep dark pockets in here but

without them, we get really just enough information to see what's going on.

So we'll keep this one for now.

Now, I've never been a huge fan of the sort of metallic gray hill shade that

is generated here.

I don't tend to like using it alone.

So, what I end up doing is something that combines the digital elevation model and

the hillshade.

And I'll go to display on the hillshade, and

I'm let's try making it 40% transparent for now.

And now, we get sort of a more glowing effect

of the hillshade based upon the elevation.

And as we get up higher the hillshade's actually even just a little

brighter from the elevation.

So, we get kind of nice effect.

I feel like it cleans up the hillshade a bit and

makes it easier to see what's going on when you do this.

One other thing to note is that we don't have to stick with grays as our color.

So we can select a different color ramp here.

And we can go from from white to kind of pinkish if we want too.

That's much harder to see, but

what we could do is go create our own color ramp as we learned how.

So, maybe what we want to do is maybe make it kind of of a grayish brown down low and

a kind of tanner deeper color up high.

Click OK.

And what we get is kind of that reddish tan.

But we still have that white coming through of here.

So, we might trick this more, but we can change the colors of our hill shape so

that we can make it suit whatever project or theme we're using.

Now, some of you might be asking,

why not just use a base map instead of making my own hillshade?

Well, there are few reasons for that.

The topographic base map is great.

I use it all the time, but for some things it's not particularly suitable.

One big issue I have it is that it ends up being slow a lot of times.

I end up spending a lot of time waiting for it to load.

So if I'm trying to get hillshade information but

also pan around the map a lot, I don't really like waiting for that.

And so for longer running projects for me it can be really handy to have my own

hillshade so that I can just turn off the base map and move around as quickly

as I want while still being able to see context for my data.

Another use case for

might be if you're working in places without reliable Internet connections.

You might want to be just be able to download one copy of your digital

elevation model, make a hillshade and

then not worry about whether your Internet is working after that.

And then lastly, from a cartographic perspective,

you might want to tweak the colors.

There's a new feature coming out in ArcGIS now called vector base maps,

where you can create your own base maps with your own data.

And then style them with basically a styling language sort of like

the web uses.

And then you can serve them up on an ArcGIS server of your own.

That requires a lot of infrastructure still, but

it might solve the cartographic problem for some of you of,

not liking the look of the existing base maps for using your projects.

Still, there's nothing quite like having a completely encapsulated

file here where I have all the data I need right here on my machine.

So, you can change the colors and do whatever you like with them.

And then lastly, if I want to save this hillshade out now,

I can kind of make my own new layer with it by going

to export map while looking at it in data view.

And I'll export it, kind of an ultra high resolution here.

900 dpi, and let's make sure actually that we select to make it a TIFF.

So we can make it a GeoTIFF by writing the world files so we can load it back in.

And I'm going to make it 900 dpi so

that we get not quite the same resolution we have now necessarily, but similar.

We could go check by seeing how many pixels wide the current hillshade is.

And then I'll have it compress it slightly with a lossless encoding

algorithm here called LZW.

And then write the GeoTIFF tags into the into image itself so

that we can bring it back into GIS.

So then if I go to, I'm about to save this out,

I'm going to call this hillshade.TIFF.

And it's drawing everything for me and processing the data.

And now I can go to Add Data and find that hillshade.

And it's a triple band hillshade, it's three colors.

And there.

And bring it in this way.

Now, what I'm getting here is a similar problem to when I bring in imagery,

where the bands are mapped to the wrong colors right now.

So, I would need to go figure out which bands are which in symbology.

Or actually, the error isn't related to the band ordering.

It's related to the stretch ArcGIS is trying to do on it.

We already have the image displayed in our existing GeoTiff as it should be

displayed.

But it tries to do the Percent Clip stretch on it, and so

we don't want it to try to stretch our color values.

I'm going to go to None and click Apply, and

then we get the TIFF as we wrote it out.

So, now I can send this hillshade off to somebody else as a single file.

And if I bring up my file browser, all I need is these files here.

I could probably even get away with just sending the TIFF, but

sending the TFW, which has some special information, is a good idea too.

And this OVR file has the pyramids for rapid display.

So if I wanted to send somebody this hillshade now, I could

just right-click and create a zip-file of it to send them off more files at once.

So, that's how we generate our own hillshade.

And kind of bake in the colors to make it a permanent

file that I can use in any other arc map document as well.

There are also some cool new l shading techniques.

One called multi-directional hillshade that you might check out.

That one's built into ArcGIS Pro and

you can install it as an extension in ArcMap as well.

And that's a pretty cool technique that tends to make way prettier hillshades,

even than the one I'm showing you here.

I mean, not that this is great shades or anything.

But you can make much more refined, clean hillshades with that

technique than you can with the standard hillshade options.

Okay, that's it for now.

In this lecture I showed you how to generate a hillshade, how to overlay it on

top of a digital elevation model, change its colors and export it out as

a permanent hillshade raster that you can use in other documents.

And talked about why you may want to do that.

Okay, see you next time.

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