In a further exploration of using PovRay to do fast calculation of Voronoi polygons, let’s look to a real stream system as an example. Here’s where the magic comes out, and where medial axes are found. Here’s the povray code: Continue reading Fast Calculation of Voronoi Polygons in PovRay– Applied
Yet further abuse to follow in the application of PovRay for spatial analyses– be forwarned… . Calculating Voronoi polygons is a useful tool for calculating the initial approximation of a medial axis. We densify the vertices on the polygon for which we want a medial axis, and then calculate Voronoi polygons on said vertices. I’ll confess– I’ve been using ArcGIS for this step. There. I … Continue reading Fast Calculation of Voronoi Polygons in PovRay
Today, I just show pictures of my process for filtering the medial axis of extraneous elements. I’ll let the pics tell the story for now: scale axis transform 3 scale axis transform 2 scale axis transform 1 previous post original Continue reading What is the center line of a complex polygon? New approach.
I didn’t remember that I had 4 previous post on this topic, but I’ve gotten a little obsessed with this problem– how to (with relatively little computational cost) kind the centerline of complex polygons, so we can extract flow lines from streams, label long complex polygons, easily generate the centerline parcel boundary line for river bound parcels, etc.. FYI, here are my 4 previous posts … Continue reading What is the center line of a complex polygon? (cont. again!)
In my previous post, a long 24-hours ago, I proposed some automatic modification of line for cartographic reasons. I had some flaws in my code. The points were over-rotated by 45 degrees. Can you spot why? Tip: it’s a basic trigonometric mistake. Here’s the corrected code (though there may be a better way): An alternate approach is to only move those points that are too … Continue reading PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines
I’m still working on this query, but I thought I’d post what I’ve done so far. My intent is to produce scale-dependent exaggeration of the distances between quasi-parallel lines. The reason for this is so that lines such as street lines which are nearly coincident at a particular viewing scale can be spread from each other, much in the same way great cartography lies a … Continue reading PostGIS Cartographic Effects– Cartoonify Nearly Coincident Lines
From earlier post: “I’ve managed to pilot most of a fast high resolution landscape position workflow with PovRay as my magic tool. The final steps I hope to pipe through PostGIS Raster. In the meantime a screenshot and description: blues are riparian, raw ocre, etc upland categories, grey is mostly flat lake plain and mid slopes, all derived from just a high res DEM input … Continue reading Landscape Position: Conclusion? (part 2)
I’ve managed to pilot most of a fast high resolution landscape position workflow with PovRay as my magic tool. The final steps I hope to pipe through PostGIS Raster. In the meantime a screenshot and description: blues are riparian, raw ocre, etc upland categories, grey is mostly flat lake plain and mid slopes, all derived from just a high res DEM input (no hydro lines … Continue reading Landscape Position: Conclusion?
Just a quick post on this one, this time. I haven’t implemented an approximation of Bálint Miklós‘ Scale Axis Transform in PostGIS yet, and I don’t think I’ll dare try in GeoTools for GeoServer just yet, but I thought I’d give a preview of the sensitivity of the medial axis calculations in “bumpy” streams with the following image: As you can see, the problem isn’t … Continue reading What is the center line of a complex polygon? (cont. 3)
I glossed over the difficulties of finding the centerline of a complex polygon in the last couple of posts, and didn’t realize the disservice until we got to the nitty-gritty of finding the centerline of “bumpy” streams, for which our solution, which is arguably a discretized version of the traditional medial axis, is quite sensitive to noise and “bumpiness”. With a little more googling, my … Continue reading What is the center line of a complex polygon? (cont. 2)
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