Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

Posts Tagged ‘Viewshed’

pov-viewshed on GitHub

Posted by smathermather on July 21, 2013

GitHub week for me:

https://github.com/smathermather/pov-viewshed

More to come, but in the meantime, enjoy.

Viewshed with Trees
Viewshed, terrain only

Viewshed Summer

Viewshed Winter

Posted in 3D, Analysis, github, Optics, POV-Ray, Viewshed | Tagged: , | 1 Comment »

Viewshed Analyses in Povray– Final Image

Posted by smathermather on January 28, 2010

I completed this project a long time ago and have not blogged on it in over a year.  None-the-less, I realized that I hadn’t posted any final images for the viewshed analysis with Povray.

So here is the summer viewshed analysis.  This is rendered with about (I think) 150,000 trees, each with 100,000+ leaves.  The cell tower here is in red.  The landscape colored in cyan where the tower can be seen from.  A property boundary shows up in green:

And here is the same viewshed but a winter scene.  Since this is a very flat wetland landscape, it’s important to understand the visual penetration of the cell tower with the vegetation, with and without leaves:

Posted in POV-Ray, Viewshed | Tagged: , , , , | 1 Comment »

Povray Viewshed with Trees (finally) (cont.)

Posted by smathermather on October 9, 2008

Ok, your average terrain-only based viewshed (view is from a road to the southeast, viewshed is in cyan):

Note that based on these estimates, we should be able to see most of the valley walls from this little slice of road.  I don’t buy that.  That section of road is pretty closed in with trees.  Let’s add them:

As you may see, just a little cyan in the southeast mostly along the road.  Here’s where you can see the trees occluding our view of the viewshed a bit.  But, it’s a first good stab, even with such boring results… .  I’ll have to get that section of road in here that peeks out over the gorge.  But first, I’ll have to see if I can get tree stem locations from the lidar, so we can trade up for some veracity in our analysis.  Stay tuned.

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Povray Viewshed with Trees (finally)

Posted by smathermather on October 8, 2008

Povray Viewshed with Trees: still some tweaking to do, especially tweaking that represents the real location and size of trees on the landscape, but if we cannot yet have veracity, best to have some verisimilitude.  Also, long term, it’d be nice if the light sources would be effected by the trees, but not the camera.  The trees occlude the ability of the camera to see what the full viewshed is.  Not clear what I mean?  Give me a few days, something nagging the back of my brain says the solution is trivial.  In the mean time, here’s the code:

Now for the include files:

light_posits.inc:

tree_coords5.inc (can you tell I’m not using version control):

Images to come of the output.  It is rendering as we speak.  I didn’t like the Povray 3.7 beta versions I ran at work on a much faster computer, so now I’m waiting for it to finish on my wife’s laptop… .

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Povray Landscape with Trees

Posted by smathermather on October 4, 2008

Just a short teaser post until I remember to bring the code home with me, but I’ve placed trees within the bounds of a canopy layer determined from some county LiDAR dataset.  The tree locations, heights, and rotation are set using pseudo-random numbers, which looks a lot better than a monoculture of the same tree.  Eventually, estimating stem locations and canopy heights to do this would be preferable, but one step at a time… .  We’ll first look for a reasonable result, and follow with an accurate one.  For now I get a pretty realistic canopy over a gorge area for a creek, so below are the first, middle-ish, and last frames in an animation I did of that canopy.

Close in:

rendering partway up…

(Check out the creek running through the gorge)

(Check out the creek running through the gorge)

And the final frame:

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POV-Ray for viewsheds (with trees?)

Posted by smathermather on September 26, 2008

In some of my first posts, I discussed the possibility of using povray for viewshed analyses, since it is a more flexible tool, and can better handle complex analyses, like terrain + vegetation, something which most GIS tools cannot.  In the end though, I just produced a simple terrain based viewshed analysis.  Now, I’m getting ready to go deeper.  Now, I’m ready to put some 28,000 trees on our viewshed terrain.

So, why not just use a digital surface model instead (an elevation model that shows us the top of all vegetation, buildings, ground, etc.)?  Well, trees, especially if there is a single row of them, are not going to necessarily block all views, so a digital elevation (or terrain) model in conjunction with an estimate of tree locations is a far better solution for accurate estimations of viewsheds.

So how do we get there?  I started with a dense LiDAR dataset with 3 returns.  I performed my analysis only on points that were either return 2 or 3, which tells me I very likely am dealing with canopy vegetation.  Then I take a moving average using (yes, I know) ArcGIS’ Spatial Analyst Point Statistics tool to determine canopy heights.

Now, to make things easy, rather than figuring out where the trees really are, I’m going to then generate random points approximately 30 feet apart, and use the elevation from my raster from the Point Statistics tool to determine the heights of my canopy.

To save on parsing time in povray, I’ll generate 28,000 non-unique trees across the landscape and see how things look.

First the code for the placement of the 28,000 random trees (written in BASH):

Now we have some random tree locations.  We make an include file of it (called “tree_coords2.inc”) that looks like this:

Now we need some trees.  I don’t want my machine to use too much memory, so a good tree “include” would be the ticket.  Pov-Tree seems the ticket here, and I’ll even use one of the pre-built trees, the Linden.

I forgot before to include the pov file for rendering:

So here’s the canopy close up:

Which doesn’t look too bad… .

And now far out:

So now we have a start for putting trees on our landscape (coming next…).

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POV-Ray for viewsheds code

Posted by smathermather on July 30, 2008

global_settings {
max_trace_level 1
}

#include “shapes.inc”
#include “colors.inc”
#include “textures.inc”

height_field {
png “c:\temp\povray\n2225625.png” // 16-bit integer digital elevation
water_level 0.0

texture {
pigment {
image_map { png “C:\temp\povray\n2225625_drape.png” map_type 0 interpolate 2 once// Aerial
rotate x*90
}
}
scale <5000, 65536, 5000>  // Scale to real world size
translate <2224868,0,625008>  // Translate to location in Ohio state plane
}

/// Orthographic Camera
camera {
orthographic
location <2227368.0, 6000, 627508>
look_at <2227368.0, 0, 627508>
right 5000*x //x size of view  (feet)
up 5000*y // y size of view  (feet)
}

// Observer Points

light_source { <2227885, 720, 625464> color Cyan }
light_source { <2228247, 727, 626277> color Yellow }
light_source { <2228091, 729, 626761> color Magenta }

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Follow on to POV-Ray for GIS Analyses–metametacode, no code yet, sorry!

Posted by smathermather on July 30, 2008

Ok, here’s the basic idea– we have an orthographic scene with a height_field object scaled to real world units. The observers in the viewshed become points of light, thus for each observer, we “light” the areas visible from each observer, render, and boom, viewshed created. In addition, if we have three or fewer view points, we can render them in, say cyan, yellow, and magenta, and thus tell which observer points can view a given location. But I digress. I keep leaving the actual code at work so I’ll start out by giving you the

Povray Viewshed Calculation Meta-Metacode:

In a Povray height_field, input elevation images are scaled 1 unit in all 3 dimensions. In our case, the input image is 5000 feet on a side in real world units. So, we multiply x and y dimension by 5000 to scale it. Since the unit values in the Z-direction are scaled to one as well, and they were input as 16-bit, that means that povray effectively divides the data by 65536, so we multiply by 65536 to get back to elevation in feet. Now our x, y, and z dimensions are scaled appropriately to each other.

Since we’re working with geographic data, well put it back in the real world (just in case we want to put other data in our system as well), in this case the Ohio State Plane North NAD83 HARN (feet) projection. So, translate to location in real space (the state plane centroid of the image) and set an orthographic camera above it with an image plane equal to the x and y dimensions. The orthographic camera prevents distortion from perspective, so we retain a flat map. (Side note: I’m contemplating using an orthographic camera and DEM to correct for terrain distortions in uncorrected imagery (and maybe shading as well), but that will take more thought, and may become another post).

Ok. Now to calculate viewshed from a point, place a point light in the scene at the location in question. Render, and boom, we have a viewshed from a point. Want a few points, add a few more point lights. Want to constrain the effect in the x, y, or z direction, add some opaque baffles (I haven’t done this in my code yet), or directional lights.

Finally, just for kicks, we can drape an aerial image on top, and our viewshed lights will only light the parts of interest, something I’ve never seen done in a GIS. But again, (see previous post) the main point is to be able to simulate vegetation, buildings and other comprehensive aspects of the scene, not just a digital terrain (elevation) model. If that’s all we wanted, a GIS would suffice. So, next step, add buildings and trees. Long term, I’d like to do this in Physically Based Renderer (PBRT) or (now that I know it exists…) LuxRender. Heck with physically based rendering, we can do some inverse modeling of physical/chemical characteristics, or WiFi placement optimizations. But again, I digress… .

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POV-Ray for GIS Analyses

Posted by smathermather on July 25, 2008

Well, I tried something that so far has been a real success. I did a viewshed analysis in POV-Ray. Nothing significant in that analysis– it’s just a topography based analysis, just like one might do in GRASS or ArcGIS. But what is interesting, is now I can add buildings (also not hard in a GIS) and trees (which can be quite hard to add). Suddenly the viewshed including trees need not be a solid wall of trees, but something partially penetrable and complex. I’ll do this in part with some new lidar data I have… and update here. In the next couple days, I’ll post the code and results I have so far. The code is very simple and not terribly flexible yet– just a test of concept, but we’ll see where we can go with this.

Posted in POV-Ray | Tagged: , , , , | 1 Comment »