Note #13
Driving scenarios

The United States Army National Training Center at Fort Irwin, California, is a unique place. It is a one-thousand square-mile classroom without walls, a 642,820-acre playing field complete with a very determined, wily "home team" unaccustomed to losing. ...

There were several reasons why Fort Irwin became the site of the Army's most grueling stateside training. For one thing the post is gigantic, with over half a million acres of usable training land. It is bordered by the Death Valley National Monument to the north and the China Lake Naval Weapons Center (home of the Sidewinder air-to-air missile and other high technology implements of destruction) to the west and northwest. Other neighbors in the California desert include Edwards Air Force Base sixty miles or so southwest and Twenty-nine Palms Marine Corps Base sixty miles or so southeast. Barstow is the nearest town of any size, and even it is thirty-five miles to the southwest of, the grim little Fort Irwin cantonment. Barstow, for the record, is more than one hundred twenty miles northeast of Los Angeles, well beyond the San Gabriel Mountains. Also, Barstow is more than one hundred fifty miles from that desert rhinestone, Las Vegas. Irwin would mean utter isolation and boredom to the average American. To the Army, it means unlimited space for maneuvers, no upset civilians nearby, and plenty of landscape in which to shoot everything from pistols to heavy artillery.

And what a savage, unusual landscape it is! The area was formed at the close of the last glacial period when several nearby volcanoes were still active. The action of vulcanism and scouring glaciers provided a mix of rocky mountain peaks, lava fields, and wide, rolling valley floors. Fort Irwin is a high desert, with an average elevation well over 1,000 feet. It is littered with igneous rock, and it has three small mountain ranges - Tiefort to the south; Granite in the western central region; and the Avawatz, straddling the northeast boundary of the post, the southern wall of Death Valley. The mountain ranges have many spurs and outcroppings, usually sloping gently to the valley floor, but in spots they rise as sheer cliffs. Irwin's climate is typical of high desert. Summer temperatures usually exceed 100 degrees Fahrenheit in the daytime, dropping into the 70s at night. In the winter months, days range into the low 80s, and nights are often near freezing. The prevailing west winds rise as the day heats up. Gusts over sixty-five miles per hour can occur, especially in the winter.

The relative humidity is low, around 25 to 35 percent in the hot season and only about 40 to 65 percent in the cold periods. Precipitation is minimal, but when it does rain, the effect is dramatic. Most rain occurs in the winter time, though even July and August have an occasional shower. The rainfall often creates flash floods, which move rapidly through canyons and washes, seeking the low ground. These floods travel long distances in the scrabbly gullies, producing a loud, rumbling noise. Naturally, these "gully washers" have a pronounced effect on the terrain. The lower slopes of all hills and mountains are laced with ditches and stream beds, and many valleys are as wrinkled as washboards from this effect. In deference to similar landforms in the Sahara, these washes also are called wadis. They range from shallow trenches to wide, high-walled cuts that are almost canyons. To soldiers, this broken terrain is a defender's delight. It offers cover from direct-fire weapons.

Plant life is very much in evidence, although the bushes and shrubs are stunted and average only three to four feet in height. Every valley and rolling slope is carpeted with yellow-green creosote bushes, the main form of vegetation at Irwin, although the shadscale scrub, alkali sink, Joshua tree, Mojave yucca, and blackbush juniper can also be found. Only a botanist can tell the difference. The plants have thick stems that can easily puncture a wandering jeep tire. At night creosote looks distressingly akin to the basaltic rock lumps that share the land with the bushes. Dismounted troops can hide in the shrubs: Vehicles cannot find such concealment. Besides rocky hillsides, sandy water-cut wadis, and valley floors dotted with creosote, Irwin also has seven dry lake beds, called playas. Each bed is the low end of a particular valley drainage system. One of them (Bicycle Lake) is an Army airfield. Archaeologists dig routinely at the playas, searching for primitive artifacts.

From "Dragons at War", by. Capt. Daniel P. Bolger, U. S. Army

Straight road

The easiest case, but we need to detect obstacles a long way ahead.

Winding roads

We might just be given waypoints at either end of the road. If the road goes roughly in the right direction, that shouldn't confuse a simple road-following system like the CMU one.

But do we have to handle something like this? Probably.

Turn at an intersection

We're given waypoints P1, P2, P3 and an allowable deviation from them. Those define the area in blue. There's no guarantee that P2 will be within the intersection, and assuming ordinary non-differential GPS accuracy, it probably won't be. It's our job in this situation to find a path similar to the one shown in red.

Underpass

Some sections of an underpass might not have enough clearance.

Detect, back out, mark as impassable and try again.

Typical obstacles

Miscellaneous obstacles in the desert. Even if we're supposed to be on the road, it's not too clear where the road is.

Impinging shrubbery

We can't let ourselves be stopped by one overhanging branch. Yet we can't go plowing through solid obstacles.

Tight fit

We should be able to handle a tight fit like this. It's a good test. The hardest part will be avoiding overreaction to the projecting branches. We can't see alongside, and our map is coarse. More short-range sensors on the sides? Feelers?

Rocky desert hillside

Rough, but we may have to pick a route through it.

We might not have to face anything this tough.

Rocky flats

But we should be able to handle terrain like this.

Our throttle and braking control system has to be smart enough to not overdo the controls on steep downhills like this.

(We can try this one. It's in the Hollister Hills Off-Road Vehicle Park.)

Gully

Go through, or go around?

Wadi

What about water? "The race will not be postponed on account of weather", the rules state. We're likely to encounter shallow crossings like this.

Deep water

The shallow crossing above looks a lot like the one at left. How do we tell the difference?

(Another Hollister Hills location.)

Checkpoint

When do we stop? Do we park, or what? If so, where?

We're not allowed to touch the vehicle at a checkpoint.