Jul 31 2008

OpenSim LiDAR sculpties – too much of a good thing?

Wow it has been a lot of effort to get the 40 regions built out with their LiDAR surface sculpties. Someday when the process gets automated I’ll look back and likely feel like a fool for not loading the BLOBs in MySQL directly, and coding the XML to load these directly. But I built them by hand, using 64-prim linked sets that covered each region. Region-wide linking works fine when the Admin settings are used to “go to God”. Also there’s a new SL client 1.20.15.92456 that works OK and helped a wee bit with the build.

My priority is to create good graphics for large-format display, but I’ve posted a rush of the first end-to end plod by the Ruth named “UC08 Visitor2”. At the moment, I’m still a bit shaky about just how solid the sim will be for demonstration purposes. None of he LiDAR surface sculpties are physical; I’ve been able to turn on ODE. I can’t bear the time to let the sculpties get meshed so there’s none of the cool walking on them, but I have tried boosting the detail settings to 64, in hopes that perhaps the sim will put out 4096 points per sculptie [my bump-maps to define each one are 16K so there’s plenty of info behind the detail boost.

As usual, if YouTube is blocked or you don’t have flash in the browser that you read this with, the video is here: http://www.youtube.com/v/srwRPgjFjnQ

2 responses so far

Jul 22 2008

OpenSim – First LiDAR reflective DEM sculpties placed

OK, not everyone in the immersive modeling universe has been holding their breath on this one, but hey, I’m happy to say that the production line is fired up and creating 2560 sculptie bumpmaps to inflate the Open Berkurodam sim using LiDAR reflective digital elevation model (DEM). The registration with orthoimagery is not perfect, and small offsets are very distracting, but the first two have been placed, and should illustrate the concept. (Two rezzed, 2558 to go…)

Sather Tower as two reflective digital elevation model sculpties

The reflective DEM sculpties have 16 times greater resolution (that’s resolution as NURB point density) than the underlying terrain megaprims. This means that for the 40-region Open Berkurodam sim, there are 160 terrain megaprims, and 160 tiles of 10-cm orthoimagery. The reflective DEM sculpties number 2560 and will be textured using the same orthoimagery.

Reflective DEM surfaces ride over the tops of trees, rooftops, or any structure. They are defined by the first return of the LiDAR reflected signal. By contrast, the terrain megaprims are based on a model of the last return (in these data up to the seventh return signal) that represents the ground under and around all structures and trees.

No responses yet

Jun 17 2008

Reflective DEM has been gridded

Published by under OpenSim

After mucking around a bit, I was able to use free tools to browse the contents of the classified LiDAR, then used ArcGIS 9.2 tools from 3D Analyst and ERDAS Imagine to get where I wanted to go with this surface. First, I needed to know how many returns there were, and what each of the classes meant. The LAStools info function helped there. Then I used ArcGIS 9.2 3D Analyst “LAS to multipoint” conversion tool, but selected only the first return. Multipoint was an annoying format because it did not seem to fit anywhere in the cool new ESRI “terrain” feature data type. In the end, I gave up on ESRI terrain and went straight to the classic TIN. For maximum overlap, I did not filter out any specific angle from nadir, taking whatever was sent along from the contractor to Alameda County.

Of course, I had to negotiate the treacherous 3D Analyst menu items that were necessary. Getting multipoint into a TIN required creation of a TIN (obvious, but with blank result) and then the non-obvious choice of “Edit TIN” which effectively accepted the multipoint data that were imported from LAS and allowed me to specify the delunay method of choice. Once canned as a TIN, it was a familiar step to specify a raster gridding. I haven’t found a way to reproject the TIN, so I was still in NAD83 California coordinate US Survey feet, and an assumed NAVD88-Geoid 2003 CONTUS-feet vertical while I tried several grid resolutions. In the end, I was happy with 1 foot gridding.

Then, raster on disk, I was able to reproject to WGS84 UTM zone 10 north meters, and chose bilinear resampling on a 25 cm grid posting interval. Once in my favored projection, I rescaled the Z values to NAVD88-Geoid 2003 CONTUS-meters, and began to examine the need for a bit of grayscale morphological processing. I’ve been a great fan of mathematical morphology for over 20 years, so it was a pleasure to craft a kernel or 3 to compensate for some artifacts. Because the TIN-to-grid was so highly oversampled, I was able to use a combination of a tall, narrow 7×3 kernel for morphological CLOSE, followed by a 3×3 DILATE, and a diamond-shaped 5×5 ERODE to finish off the task. In case this morphological stuff sounds like odd stuff to do, these operators are variations on focal max and focal min convolutions. The results are rather important for my application, as shown in the following images.

First is the reflective DEM surface, and the same with the Open Berkurodam 40-region overlay.

This is the gridded reflective DEM here it is with the OB40 image overlay

Next are more detailed images, near the Greek Theater, showing why I ran the morphological filtering and also how I was able to mostly conserve building footprint areas while inflating trees. The main artifact attenuated was interlace-type effects at the end of overlapping LiDAR scans. The long axis of the morphologcial CLOSE kernel was perpendicular to these artifacts.

Here is the reprojected and rescaled reflective DEM, unfiltered Same area, but with morphological filtering as sketched above

Here is the morpho-filtered reflective DEM, with the 10 cm natural color imagery overlaid.

overlay of natural color image on morpho-filtered reflective DEM

Next up, I’ll need to figure out how to best use this 25 cm surface. It really seems a shame to use it in the way that I have thus far with terrain megaprims–where using four megaprims per region I have effectively downsampled the terrain to 4.26-meter grid postings. That wasn’t so bad for the bare earth model. Here I’ve got something over 290 times denser with 0.25-meter grid surface samples.

But to use many more than 160 megaprims for the entire 40-region model, I really must automate the placement of the (auto-generated) sculpties. For that, I’ll need to ask around the OpenSim community for advice!

No responses yet