GIS 300 Week 7: Viewshed analysis of a trail in QGIS 3.16

good morning gis 300 it is time to get into some terrain analysis specifically visibility analysis where the question is what can you see from here or vice versa from where can you be seen now you may already know from for 242 or prior knowledge that you can get the view shed from a single point in google earth you do that by creating that point placing it where you want to be there on the pike towards the knife's edge hit okay right click and show viewshed it'll ask you if you want to automatically adjust so it's two meters above the ground that's where the eye should be adjust automatically it'll think about it for a moment and then once that's done it'll give us a hopefully correct view shed which gives us a pretty decent view there i mostly believe that if you see an all green circle here you have to check on the button for terrain if you don't have the terrain jacked on of course it's not going to work at all so you can allegedly see all of this and all of this but i can't see the elevation model i can't see exactly where the highest point is and i can't show the view along the entire trail all of those things i want to do so first of all we need some lidar data we want to have a lidar data set because one we have it that's wonderful and two it's going to be the most accurate and we want to use our lidar derived data set to do this so search noaa lidar from the coast.noaa.gov noaa data access viewer elevation slash lidar and then go ahead and zoom in on katahdin and you can check on the satellite image there so you can see where you're going it's a little bit low there and there's katan now we're going to evaluate the a-ball slide trail or whatever has replaced it or maybe the hunt trail so we're going to use our dropbox and we're going to click hold drag and release a box that shows about that area can't go too big on this because this is a very big data set almost a billion points there you don't want to go much over a billion points it starts to bog down so click there add to cart and from there go to the cart and say next we want the output product to be a raster we want the grid method to be a spline i've tested out all the different methods for this for this location and this one fills in some gaps that persist with the other methods and we want to change that grid size to five so that's going to be a five by five meter raster grid and that's a pretty good balance i'm finding between the the precision that can come from linear and computational time finally let's change this to utm zone 19 north and hit next go ahead and give it your email not mine and then hit next again review your order and submit and in due time you'll have an email that looks like this one this order has been split into a number of different parts looks like about 20 different tiff image files which we'll have to stitch together so i'm going to click on that download link which will take me to a zipped or compressed file which hold on have to extract that's finished downloading now and here's my zipped folder which i then have to extract here i'm going to browse and place that in my gis nt gis 300 week number seven select that folder and extract now normally we would add data in through the browser tab but here we actually want to stitch them together before bringing them in under raster miscellaneous merge we have to select the inputs here and then i'm going to add directory and i'm going to go to where i just saved that which is gis 300 week number seven select that folder and here is an interesting issue that i've been having where this is the last thing i did one of the test trends i did for this you see how this is the anu dem thing this is sort of held over in its memory it seems so i need to clear all that and let's see if i can add the directory again see this is where it was before it just got a little confused there so i need to select week number seven and there is week number seven so check your file path there if this is your first time doing it you shouldn't have this problem but there you go so i also want to uncheck these other things that i don't want stitched together these are other files that i have in the same folder and this dot xml doesn't want to be checked on either once i've got the ones i want here then i hit ok now i'm going to scroll down save to a temporary file and run and when that finishes i end up with this merged together this is all of the different rasters stitched together into one and i like this so i'm going to save it permanently right click export save as and now i see that i made an error here so sometime while i was exporting this or telling noah digital coast what i wanted exported it switched itself back to one one one by one meter resolution that's fine it's going to give you a very nice view of this thing but for you i recommend 5x5 it's going to take a lot less time to process or if you have a very fast computer by all means go with one by one meter resolution so this needs a name and i'm going to plot that in week 7 and i'm going to call that the viewshed dm because that is the elevation model i'm going to use for my viewshed okay that loads there and now i can right click remove that layer and we're ready before we get started we can do some things like change the min max value settings to the updated canvas which means the highest and lowest values are always going to be calculated within this screen which is good for when you want to see what the highest point is so i can see pretty well somewhere in here is going to be my high point but this color wrap isn't the best for that let's change that double click instead of single band gray single band pseudo color and i'm going to use this default ramp classify it but i want to actually invert that color amp so there you go and then i'm going to go to my min max value settings and set the statistics exact extent to the updated canvas again okay and i had to zoom in and out once to make that go from all red to display as i wanted now as i zoom in i can see which ones within this view are the highest it's either going to be one of those and then i can use this identify features tool to get the exact values of 5248 0.84 0.64 0.84 so this is the top point that's going to be important when you do your view shot analysis because if you're not on the highest point if you're here instead of here this could block your view when you're really trying to answer the question of what's my view from the top now let's make this look a little bit better with a hillshade model right click duplicate layer and then double click and instead of single band pseudo color he'll shade okay uncheck that one check that one on that's the traditional hill shade i don't love that for todd so let's try the multi-directional apply that that's a bit better i want to change the z-factor to 2. i like that for that kind of a model and i'm going to change that brightness to drive 40 apply there 60 apply there 80 apply there pretty difficult with this very steep terrain but let's look at what this looks like with the elevation model on and we're going to move this over and change the transparency and we'll set that down to try 65 percent that's looking a bit better let's try that that's looking pretty good so as we zoom around let's see how that changes pretty good pretty good that gives a very nice view of the knife's edge which might be important soon next we're going to open up the trails network for the state park and see that this does not exactly follow along the exact ridge here that's going to be a bit of a problem we can see looking at the air photo though that is a bit off but the trail of pamola peak is pretty well dead on so you know what i'm gonna do i'm gonna digitize my own representation of the knife's edge and i'll have you do the same because when you look at this with your five meter resolution elevation model you should follow along the highest points on your trail it could be slightly different so what we're gonna do right click on your working folder new shapefile going to call that a geometry type line and we're going to use utm zone 19 north and let's see we have location we have a type we have a coordinate system don't need fields yet so go ahead and hit ok and now we have a new trail line here and what did i just call it new layer i should have given that a name but i can rename that here i'll call that knife's edge and i'm going to make that a nice bright red simple line a bit thicker and we'll make that a nice bright red okay okay good to go so what i need to do is right click on knife's edge toggle editing and now i can add new features so this one here add line feature click that and now we're working with that tool go ahead and zoom in on where you want the start to be and i'm going to start from pamela peak and then i'm just going to click along and i'm just going to connect the high points here is that going to be exactly right maybe maybe not but i think it gives the best representation of the knife's edge trail and what you might expect to see from them so the end result of all of this is what can you see as you're walking along here and which of these points has the most visibility and of course the knife's edge gives you a great view you know that even if you haven't been up there one look at this you can tell well this is about as high as you can get in the state of maine and you have pretty good unobstructed view all the way around so we're going going and going but of course there's places you can't see there's a whole mountain in front of you in some places you can't see what's on the other side and sometimes there's such precarious going that you're not really even looking around here trying to look for a handhold and not fall to your death so we do for fun right right carrying along carrying along so every time i click that adds a vertex so we're creating points the line oh run off base there ctrl z doesn't let me do that oh well so we're just gonna go with that and we'll just call that a happy accident we're doing gis bob ross now and forgive you for fast forwarding through this if you do we'll get there we're getting close to baxter peak now and we'll just keep following this ridge along and down a little off it there that's okay or happy accidents and we'll end there okay and there it is so now we can see we have a new trail or a new representation of that trail that follows that ridge line of knife's rage exactly so we can get a quick estimate of the length of this line by just more or less following along there total thing about 1400 meters close now we want to create some points and we have a tool to create points randomly along this line which is actually not bad from a statistical perspective because we don't really have any regular interval by which we'll know we'll be looking so as we walk along at some random points we'll turn around and take a look so let's go ahead under vector research tools random points on lines and we're going to use the knife's edge as an input we're going to generate 100 points where we'll take a look around us and we'll say give us a minimum 10 meters between points should do and go ahead and run that close so it looks pretty good not perfectly evenly spaced but randomly enough to be believable as you're walking along taking this hike and look it includes just about the end of baxter peak there so that looks like a reasonable representation of all the times a person might break their head up take a look around as they're hacking across the knife's edge now we need to install a plugin and i think we've talked about this before but qgis is built around plugins the language that the program itself is written in is open source so you can read that language and then speak that language back to it give it instructions for how to do a specific task and in this case that task is visibility analysis so plugins manage install plugins and let's see what i have installed here so i have profile tool i have visibility analysis i'm going to uninstall that because i need to show you how to install it so that's going away now i go to all so all here search visibility analysis this one click once install plugin it'll load what it needs bring all that in close and now that's installed over here in your processing toolbox you have a variety of tools if you don't have processing toolbox under view panels processing toolbox and after you've installed this plugin you'll see visibility analysis at the bottom and you can open that up we need to do two things first is prepare the data under create viewpoints double-click observer locations the random points on the lines and the digital elevation model is our few shed dem in this case that's what i've called my elevation model and we have the observer ids and we want to change that to the random point id i'm going to keep the radius of the analysis and i'm going to keep the observer height as standard defaults there keep all the rest and create a temporary layer go ahead and run so that's just loaded information about those points onto those points you see how they changed color and now we're working with this output layer and not the original random points on lines so now these points know what they're going to do now we need to go into analysis and view shed double click and our analysis type is binary viewshed our output locations are the output layer we just created and the digital elevation model is our same elevation model from before we have some options here with how to combine multiple outputs but we're going to keep the default save to a temporary file hit run and expect this to take a little while and 25 minutes later the view shed analysis is complete go ahead and close that here is our trail which is represented by 89 points now i did ask for 100 points but i told her they couldn't be any less than 10 meters apart so we dropped the number a bit this is our trail and the lighter the color the more times it can be seen from the trail zooming out a bit we can see the wider view shed here and the edge of that five kilometer radius so all of this area the table lens is not visible from the knife's edge because oh there's a whole mountain in the way but now we want to know which point has the best view this can be the tricky bit so we're going to go under view panels log messages and then over to view shed info what you see here is a comma delimited data format we have to copy the point id all the way down here and then ctrl c now i'm going to go into notepad and if you're on a mac i'm not sure if this is the same it might be if it isn't we're going to have to figure it out you see how we have point id comma visible pixels comma total pixels and then all of that i can go file save as and i'm going to save that in gis 300 week number seven and see it's only giving me one option there that's a bit of a lie so i'm going to call that visibility dot csv comma separated values csv and see if naming at that makes it so a csv file this is essentially the boundary between one column and the next column in a spreadsheet so here we are visibility as a csv i need to close this one first so bye bye and then i can double click on that and there it is in excel so it knows since it's a csv the comma means different row now i want to change this no space spaces are terrible in names so visible and then total so point id visible total save it's going to ask do you want me to keep using csv essay yes yes i do thank you very much click out of that and this is the tricky bits so you do have to say don't save you did just save but it gets confused if you say save again it asks you again so don't save that's fine now we can go ahead into week number seven we're going to have to refresh this and with that refresh done we can go ahead and look for that and we are looking for visibility.csv which we can double click and bring in and we can right click and open that attribute table take a look at our data yes that looks good thank you very much and now we can go ahead and take our output layer right click properties and go to joins just like we did with the bearer and moose data and deer too go ahead and add a join here and we want to use the join layer visibility the join field point id target field id and now okay and okay now remember these are unstable right after a join you have to export to make a permanent feature so right click export save feature as i'm going to save this in week number seven and that is visibility points area dot shp all else looks good okay okay and there we go new points layer now i'm going to right click on that open its attribute table and take a look here so we have visibility and then that visibile one so that is the number of pixels each pixel is one meter square or one square meter and the visibility one that is the potentially visible area that is the radius five thousand meters or 5 kilometers less the area that's off the edge of that dem data layer so in some cases we have a five kilometer radius in other cases well that hits the edge of the map there and there may be monsters out there but there is no elevation data but to the point now we have the visible area from each one of those points which we can right click symbology graduated value [Music] now it's not doing the graduated option there because our visibility is text and not a number so right click open attribute table visibility there that's just text so it needs to be a number let's see if we can fix it this way so we want to create a new field the output is this area and we'll call that yeah whole number there's no fractions there and that just equals visibility so let's see if we can convert that preview looks good okay same number same everything but now if we go in here let's toggle let's toggle the editing here tab editing save the edits double click there there's a sad noise wasn't it and then we want graduated and now ha ha we have it there's a lesson on data types now classify we have from smaller to greater visible area from each one okay there you go so you can see more according to this model from the ones that have a darker red and why can we not see the most from the top of baxter peak go ahead and turn off that and that oh well we missed the high point so the high point looks like it's somewhere other than where our points fell so that if you really wanted to know what you could see from the very peak of baxter peak then you would have to put a dot right on top of it and that would almost definitely get you the best view so that's one of the perils of having a crazy high resolution data set where it's pretty easy to go off track might be a touch better with a five meter resolution that'll give you a little more room for error right now my margin for error is one meter and if i put it behind a rock it's behind a rock and you can't see much so picture this laying out a road in a national park you want to have the best view from the park so you can pick a couple of different potential routes and then see what the visibility is from each which one is going to give you the most bang for your buck you can only build one road so which one gets you the best view way back in the day before gis this is still a known concept and when the carriage trails down in acadia national park were built for the rockefellers who owned it at the time the landscape architect was very careful to make sure that every time the road made it turn you had what they called a vista and that vista is some beautiful view so as you're coming up on that turn hopefully not getting distracted and driving off the edge of a cliff but you'd have some nice view out over a pond or an ocean or something waterfall mountain something so you would have the biggest visual impact as you're going around that curve on the other hand if you're building a road and you don't want that road to be seen from somebody's house you might be careful to make sure that the visibility of the view shed from that house does not line straight up with that road there's just a ton of uses for this and i want you to do two things here one go ahead and replicate this analysis use the five meter resolution data set don't mess up like i did and get the one meter if you do try again it'll speed things up and then pick one other spot of your choice so two visibility analyses one like mine one of your own choice

Channel: UMFK Forestry

Views: 412

Rating: 5 out of 5

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Id: YBo-frNIz5Y

Length: 25min 15sec (1515 seconds)

Published: Fri Mar 05 2021