Google Earth image Rendering of STL file Photo of finished carving
Keu­ka Lake (Google Earth) Com­put­ed STL sol­id mod­el Fin­ished prod­uct

It start­ed when L. spot­ted an arti­cle in Ready­Made about Flu­id­Forms, a com­pa­ny which makes cus­tomized “Flu­id Earth bowls” out of wood. You go to their Web site, select a geo­graph­ic area of inter­est, and their com­put­ers carve a scale mod­el of that ter­rain out of a slab of wood. In the­o­ry you can use it as a bowl for your veg­eta­bles.

“That’s easy,” I decid­ed. We had recent­ly acquired a 3-axis CNC router at work, and although I didn’t yet know how to use it, I fig­ured it would be sim­ple enough. We were slat­ed to vis­it New York’s Fin­ger Lakes region in a cou­ple of weeks, so an obvi­ous first project would be a gift which shows the ter­rain near her family’s lake house. Now, for the data.

Google Earth was the log­i­cal start­ing point, since every­one knows how to use it. Unfor­tu­nate­ly, it is also a closed-source com­mer­cial pro­gram. They make it very easy to put data into it, but for var­i­ous rea­sons it is very dif­fi­cult to get data back out. NASA offers a sim­i­lar appli­ca­tion called World Wind which solves the open­ness prob­lem, but the full fea­ture set is only avail­able on the Microsoft Win­dows ver­sion. What to do?

The solu­tion was pro­vid­ed by the US Geo­log­i­cal Sur­vey, which oper­ates a Web ser­vice called The Nation­al Map Seam­less Serv­er. The USGS pro­vides a vari­ety of geo­ref­er­enced data prod­ucts free of charge. These are nor­mal­ly divid­ed up into rec­tan­gu­lar quad­ran­gles which do not nec­es­sar­i­ly cov­er the entire area of inter­est. But the Seam­less Serv­er can qui­et­ly stitch togeth­er mul­ti­ple maps. You sim­ply select the area of inter­est, choose the data prod­ucts you need, and down­load them.

Flu­id­Forms, like Google Earth, relies on world­wide ele­va­tion data from Feb­ru­ary 2000’s Shut­tle Radar Topog­ra­phy Mis­sion. NASA cal­cu­lat­ed the height at every point on the Earth’s sur­face using space-based radar inter­fer­om­e­try. Because it is based on radar reflec­tions, it is not tremen­dous­ly accurate—it can’t dis­cern between dense tree­tops and the ground, for example—but it does cov­er most of the Earth at 30 meter res­o­lu­tion. But because I’m mod­el­ing loca­tions in the Unit­ed States, the USGS offers me a bet­ter choice: the Nation­al Ele­va­tion Dataset. The NED is derived from a vari­ety of sources, includ­ing tra­di­tion­al sur­vey­ing, and is large­ly hand-checked for accu­ra­cy. It is avail­able in ridicu­lous­ly high res­o­lu­tions (present­ly 10 meters, with 3 meters com­ing soon). As a result, even lit­tle streams and creeks are vis­i­ble. Per­fect!

The next step was to find a pro­gram to con­vert down­loaded ele­va­tion datasets into 3D sol­id mod­els in a for­mat that could be under­stood by com­put­er­ized man­u­fac­tur­ing tools like 3D print­ers and CNC routers. I quick­ly dis­cov­ered that no such pro­gram exists, so I wrote one. The cho­sen DEM data for­mat (Geo­T­IFF) as basi­cal­ly a grid of float­ing-point alti­tude val­ues geo­ref­er­enced to the UTM coor­di­nate sys­tem. Had I been inter­est­ed in a larg­er area, I would have had to “unwrap” the Mer­ca­tor pro­jec­tion onto a spher­i­cal or ellip­ti­cal sur­face, but because the lake is rel­a­tive­ly small, I decid­ed to forego the extra math. The pro­gram sim­ply applies the prop­er scal­ing fac­tors and adjusts the Z-height to reflect the desired min­i­mum thick­ness of the wood. The sol­id mod­el out­put is in STL for­mat, which is basi­cal­ly a giant mesh of inter­con­nect­ed tri­an­gles in 3D space. Each tri­an­gle is described by 3 ver­tices and a unit nor­mal vec­tor to tell the com­put­er which side is the out­er sur­face. For sim­plic­i­ty, I turned the entire X-Y grid into tri­an­gles. The pro­gram con­nects the tri­an­gu­lat­ed sur­face with yet more tri­an­gles which describe the sides and bot­tom of the fin­ished prod­uct. Done.

Unfor­tu­nate­ly, in my zeal for detail, I dis­cov­ered that STL files with more than one mil­lion tri­an­gles can choke even a pow­er­ful com­put­er. Ide­al­ly I would reduce the num­ber tri­an­gles in non-detailed areas, but such algo­rithms are beyond my skill lev­el. I’m just an elec­tri­cal engi­neer here. I wound up reduc­ing the res­o­lu­tion of the whole area.

With the STL sol­id mod­el com­plete, all that was left was to gen­er­ate toolpaths—the actu­al motions that the CNC router will fol­low while carv­ing. For­tu­nate­ly, the router comes with CAM soft­ware to accom­plish this task.

For our first piece, we lam­i­nat­ed 3 pieces of Baltic Birch ply­wood with PVA glue. The out­er dimen­sions are 16 x 14.5 inch­es. The carv­ing takes about 3 hours: a first pass with a 1/2″ diam­e­ter mill roughs the wood down to the approx­i­mate shape, then a final pass with a 1/8″ ball-end mill cre­ates the final sur­face. After about an hour of sand­ing and a cou­ple coats of Dan­ish oil, the bowl was done. Suc­cess!

May 31, 2008 May 31, 2008 archives by Scott 3 Comments

I passed a bus ear­li­er today shrink-wrapped with a Nation­al Grid adver­tise­ment boast­ing that “by run­ning on nat­ur­al gas, this bus saves 54 tons of car­bon from the envi­ron­ment.”

To which I say: what’s so unde­sir­able about the Earth’s sec­ond most abun­dant ele­ment by weight? The sole com­po­nent of graphite and dia­mond? The key to turn­ing ordi­nary iron into steel, which brought forth the Indus­tri­al Rev­o­lu­tion? The basis of organ­ic chem­istry? The chem­i­cal basis for all known life?

Maybe they meant “car­bon diox­ide.”

While we’re on the sub­ject, we need to imme­di­ate­ly stop the spread of the vogue term “car­bon foot­print” before it takes over the world. Its brevi­ty makes it a poor choice for explain­ing how glob­al warm­ing works. It also recalls oth­er irri­tat­ing­ly bad abbre­vi­a­tions of this decade, such as the use of “ter­ror” to mean “ter­ror­ism.”

May 22, 2008 May 22, 2008 archives by Scott No Comments

Grover Norquist was the guest on the Col­bert Report last night. I am apalled by his bla­tant over­sim­pli­fi­ca­tions of obvi­ous­ly com­plex issues—he claims that the fed­er­al gov­ern­ment should pro­vide lit­tle more than safe­ty and secu­ri­ty (to which Col­bert teased that we could prob­a­bly do with­out the Inter­state High­way Sys­tem too).

But I can appre­ci­ate his theme of reduc­ing unnec­es­sary gov­ern­ment restric­tions on com­merce and pri­vate life when­ev­er pos­si­ble. So I won­der: why are the Repub­li­cans not the biggest cham­pi­ons of legal­iz­ing gay mar­riage?

May 15, 2008 May 15, 2008 archives by Scott No Comments

This com­par­a­tive analy­sis of the 50 largest Amer­i­can cities is a trea­sure trove of infor­ma­tion and clever analysis—one which could be the spring­board for a thou­sand future con­ver­sa­tions.

One of my favorite met­rics is the ratio of eth­nic restau­rants to fast food restau­rants. Boston ranks well at #3. Cincin­nati is at the bot­tom of the list (#50).

May 6, 2008 May 6, 2008 archives by Scott No Comments

The country’s first all-plas­tic road bridge is being built in my old neigh­bor­hood in Cincin­nati.

April 26, 2008 April 26, 2008 archives by Scott No Comments

It’s always fun to see your home­town on the big screen, but this film is bet­ter sum­ma­rized as “two hours of my life I’m not going to get back.”

Also, my $6 bag of pop­corn was repul­sive­ly bad. Thanks, Regal Cin­e­mas.

April 23, 2008 April 23, 2008 archives by Scott No Comments

A cap­tion on the Boston Globe web site says that Prime Min­is­ter Gor­don Brown “will speak today to Boston” at the JFK Library.

That state­ment is sim­ply untrue. I checked, and in fact the whole library is closed for the day. (Boston was not invit­ed.)

April 18, 2008 April 18, 2008 archives by Scott No Comments

Sun­day, after the race, L. and I dropped by the Smithsonian’s Hir­sh­horn Muse­um and checked out their exhib­it “The Cin­e­ma Effect: Illu­sion, Real­i­ty, and the Mov­ing Image.” The qual­i­ty of the pieces was all over the place. But the unmis­tak­able whirring of a large film pro­jec­tor (heard from an adjoin­ing room) led me to my favorite piece: Rod­ney Graham’s “Rheinmetall/Victoria 8.” In a room by itself, on a plat­form, a giant 1961-vin­tage 35 mm film pro­jec­tor (the Vic­to­ria 8), equipped with a clever auto­mat­ic loop­ing device for its 10 min­utes of film, clat­tered away effort­less­ly. It was pro­ject­ing a film of an even old­er type­writer (the Rhein­metall) being dust­ed with snow. The pro­ject­ed black-and-white image was pow­er­ful, bright, and gor­geous­ly contrasty—standing in sharp con­trast to neigh­bor­ing exhibits with lack­lus­ter dig­i­tal pro­jec­tion. But despite the com­pelling yet inan­i­mate sub­ject of the film, I found myself drawn like a mag­net to the pro­jec­tor. The intense glow from its lam­p­house seemed reluc­tant to be con­strained by its enclo­sure, spilling out of every crack like sun­light through the walls of a dark barn. The film spool­ing out of the infi­nite loop plat­ter moved swift­ly and smooth­ly. It was beau­ti­ful mechan­i­cal har­mo­ny, and great art.

April 9, 2008 April 9, 2008 archives by Scott No Comments