May 03 2008

Terrain Megaprim Sculpties – HOWTO

Published by at 1653h under SL In General

Today I would like to share the inside production notes (it’s quite low tech for the most part) on making terrain sculpties. I have included a full region’s worth of working raw terrain, and a set of four megaprim sculpties that should help to clarify some of my mutterings in earlier posts. Stuff like precisely which values go into the sculptie gradient maps (shown in a spreadsheet), what it looks like when one takes textures that are 960×960 and add a 64-pixel-extent collar around them, and how to actually configure a region to load and display the 250-meter square at Military Grid Reference System / US National Grid 10SEG_6550_9200, with all the necessary bumpmap and texture files, and instructions for both OpenSim console-side and SL client-side actions.

obdam_40h_php This is how I have created the 40 regions using MGRS / US National Grid naming convention, particularly if the terrain has been scaled to 1.024:1 so that exactly 250×250 meters of RL terrain are loaded into each OpenSim region.

obdf_2_7_f32 This is a single region’s raw float terrain file. The original input digital elevation model had been gridded to have postings every 30cm in X and Y. The nominal scale for OpenSim terrain is 1 meter in X and Y. For large grids of real-world regions, there is reason to scale things up slightly so that there are exactly 16 regions per square kilometer. When one does this, as I have here, the samples are 977 mm and the real-world scale is 1.024:1 or a couple of percent larger than life.

sculpt_gradients_132 is the magic for the sculpties, all one needs to do is take the precise spreadsheet values and create three 8-bit grayscale images from them, using a raster program of your choice, to fit 132×132 size for use as a starting point. Then in the middle 130×130 area of the Z-value image (third or blue channel), insert your 8-bit rescaled values of terrain surface. After that, stack the X, Y, and Z grayscales together as Red, Green, and Blue channels to make a single RGB that will be your UV bumpmap.

Working Example single terrain megaprim bumpmap and texture
This is a single sculptie bumpmap+texture set intended to be placed on a megaprim named ‘nw’ that is sized with ‘edit-scale nw 132 132 164’ on the OpenSim console.

Full 1.024:1-scale region with f32 terrain and four megaprim terrain sculpties This is the real deal, one of the 40 regions in the Open Berkurodam sim and I think it’s an interesting part of its steeper area. The link is to a 10MB zip file that is named for the 250-meter square MGRS/US National Grid region that it represents: 10SEG_6550_9200, the grid point at its southwesterly corner. This archive contains a single-float terrain “obdf_2_7.f32” raw file ready for loading into an OpenSim region; the file name results from a raster dicing script and this is the second region down and seventh region over from the northwesterly corner of the 40-region sim. The archive also contains four pairs of bumpmap+texture Targa files; their file name results from the same dicing script but the indices are higher because these are quarter-region areas.

10SEG_6550_9200_xml Region configuration file for the following example (I neglected to include it above)

To try out the full region set, take an available OpenSim region, and load in the terrain from the OpenSim console with the following sequence

change-region 10SEG_6550_9200
terrain load obdf_2_7.f32
terrain bake

Next, seed the region with four prims. I tend to fly into the middle of the region or teleport and turn left 90 degrees so I am facing northerly, drop four cubes a few meters apart, then name them by their quadrant: ‘nw’, ‘ne’, ‘sw’, and ‘se’, ensuring that the Prim’s new names have stuck by checking at least one. Then I fly to the outer edge of the region, or just over into the next southerly one. This is not strictly necessary, but it feels like the right thing to do, sort of like walking a safe distance away after having set four large underground charges. That’s because the next step involves super-sizing. In my lab, the OpenSim server is an Ubuntu Linux box running Mono 1.2.6, but my SL client is on Windows XP, and I switch between machines on a KVM switch going from the OpenSim console to SL client, and it is so much easier to see the megaprims if you aren’t inside them after they have been inflated. On the console:

edit-scale nw 132 132 164
edit-scale ne 132 132 164
edit-scale sw 132 132 164
edit-scale se 132 132 164

The Z value is the one I use in the steepest part of the sim, and this makes some really big cubes. I tend to pull them apart far enough to tell them apart.  Be careful here–I’ve hung a sim that was running fine for a week by planting the seed prims not close to the center and then dragging the centroid of the megaprim over into the next region. Sometimes when handling these megaprims it’s handy to ensure that you have the SL client’s draw distance maxed out to 512 meters, and also to zoom the view out from default one notch with “CTL-8” to trade of field of view with distance from the prims you are handling. So when you’ve got one of the megaprims selected for editing in the SL client, move them into position by keying locations into the Object tab while being very careful not to touch the values in the Size category (thus saving yourself a visit back on the OpenSim console to reinflate the megaprim) When using but four terrain sculptie megaprims per region, their positions in X and Y are always the same, and the Z position will depend on how you’ve rescaled your floating-point terrain to fit into the 8-bit unsigned approximation. For the example megaprims that I have posted, use these:

Prim ‘nw’ XYZ = 64, 192, 188
Prim ‘ne’ XYZ = 192, 192, 188
Prim ‘sw’ XYZ = 64, 64, 189.5 (tweaked for amphitheater vs. region terrain)
Prim ‘se’ XYZ = 192, 64, 188

Once I can see that the prims have snapped to fully cover the region and are all nearly the same height, I change their Building Block type to Sculpted and see four really large apples that may be somewhat subterranean. If I hadn’t already done so, I use File > Bulk Upload to get all the bumpmap and texture Targa files into inventory. When you have four megaprim sculpties, you should choose the following for Object/Sculpt Texture and Texture/Texture:

Prim ‘nw’ Sculpt = ‘ob40_03_13_z3.tga’ ; Texture = ‘ob40e_03_13.tga’
Prim ‘ne’ Sculpt = ‘ob40_03_14_z3.tga’ ; Texture = ‘ob40e_03_14.tga’
Prim ‘sw’ Sculpt = ‘ob40_04_13_z3.tga’ ; Texture = ‘ob40e_04_13.tga’
Prim ‘se’ Sculpt = ‘ob40_04_14_z3.tga’ ; Texture = ‘ob403_04_14.tga’

For the sort of appearance that looks best at first, I have kept the background color in the texture to all 255’s and set the Full Bright to checked. That setting does not do well when it’s night in the sim, but it overcomes some sort of fade that is visible in the texture around the edges of the sculptie when Full Bright is not set. More improvements for the future!

Deep thanks to Adam Zaius for pointing out that I hadn’t really made clear these details in the blog. Enjoy!

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