# New scent detection algorithm integrated into Dinosaur Island.

The finished equation for determining the probability of a dinosaur detecting the smell of another given wind direction, velocity, distance and bearing. Click to enlarge.

Above is the equation for calculating the probability that one dinosaur can smell another dinosaur given the wind direction, wind velocity, distance and bearing of dinosaur one to dinosaur two. A great deal of work went into this equation and I must thank my good friends and colleagues, Alberto Segre and Mike Morton, for all their help, feedback and encouragement.

Below are examples of the output of the equation with various wind direction and wind velocities:

Results of the equation showing likelihood of detecting a scent at a specific location given the wind direction and wind velocity. Each square is 100 meters.

Results of the equation showing likelihood of detecting a scent at a specific location given the wind direction and wind velocity. Each square is 100 meters.

Results of the equation showing likelihood of detecting a scent at a specific location given the wind direction and wind velocity. Each square is 100 meters.

Below is a screen capture from Dinosaur Island showing the results of the new scent detection algorithm (coupled with the newly added olfactory acuity variable, see New sight and smell variables added to Dinosaur Island).

Screen capture of Dinosaur Island with new scent detection algorithm integrated into the AI. Note AI output on right (highlighted by red box): Gertie, the Edmontosaurus, cannot see Jim, the T. rex, but she can smell him. Click to enlarge.

While developing the scent detection algorithm and reading about the extent and frequency of injuries sustained by T. rex (broken ribs appear in about 25% of known T. rex fossils) it seemed very likely that an old T. rex (and T. rex did not achieve sexual maturity until their twenties) had to be a very cautious hunter. An Edmontosaurus regalis tail could break T. rex ribs if the Edmontosaurus was aware that the T. rex attack was imminent. As we will see in the next post, a smart hunting T. rex must have had to employ clever tactics to avoid both visual and olfactory detection as it approached its prey.

# New AI enables T. rex to anticipate prey’s future location.

In this screen capture from the Dinosaur Island AI testbed program a T. rex (John, left) is stalking an Edmontosaurus (Muffie). The long yellow line intersecting the shorter yellow line is where John anticipates that Muffie will be 40 seconds in the future and he is planning accordingly. The blue lines are angle of vision arcs (140 degrees for Edmontosaurus, 55 degrees for T. rex). John can see Muffie. Muffie cannot see John. Click to enlarge.

We recently added ‘blinders’ to the dinosaurs by restricting their ‘vision’ to accurate angles calculated from the position of their eye sockets in their skulls (see new sight and smell variables added to define dinosaur species).

After restricting the T. rex’s vision to 55 degrees we observed some unexpected behavior: while pursuing prey a T. rex would occasionally ‘lose sight’ of his target and not be able to reacquire it. Upon investigation we discovered that the cause of this was that the T. rex would advance, single-mindedly, towards where the prey is now. Under some circumstances, and if the simulation’s ‘time slices’ were sufficiently larger (> 8 seconds), and if the prey moved away at an oblique angle, or disappeared behind a hill, it was possible that their prey was no longer observable within the restricted angle of vision.

The solution was to give the T. rex the ability to anticipate and calculate its prey’s position in the future.

If we simply wished to use ‘cheating AI’1 the solution would be trivia. Because the current goal for every dinosaur is stored in memory a ‘cheating AI’ could simply look up the objective for its prey and arrive there first. That is not what we did.

Instead, if the T. rex sees a prey animal and begins stalking it the future position of the animal at X seconds2 in the future is calculated given the prey animal’s bearing, current speed, expected terrain traversal and anticipated slope traversals.

Again, we must ask: are we making the T. rex too smart? At this point; we must be pushing the extreme levels of dinosaur calculations and planning abilities. However, as a predator – and there is solid evidence that T. rex was, at least, occasionally a predator –  he must have possessed the ability to calculate future positions of prey animals. Furthermore, he must have been very familiar with his hunting territories and, consequently, possessed a priori knowledge about terrain and slopes.

This AI technique probably makes a hunting T. rex in Dinosaur Island the most advanced NPC (Non Player Character) in all current computer games.

1) Cheating AI: There are numerous examples of ‘cheating AI’ in computer games. Without going into specific details, some of the more common methods include giving the computer AI information that should be hidden (such as enemy unit positions and intentions) and weighting random factors in the computer’s favors. See also Artificial intelligence (video games) and The Computer Is a Cheating Bastard.

2) X seconds: we are currently using 40 seconds as the future point in time for anticipated position calculations.

# New sight and smell variables added to define dinosaur species.

Two new values have been added to describe a dinosaur species: Angle of Vision and Olfactory Acuity. Screen capture (click to enlarge). Note: the T. rex Angle of Vision has been increased to 55 degrees per, “Binocular Vision in the Theropod Dinosaurs by Kent Stevens”.

We’ve added two new variables to describe a dinosaur species: Angle of Vision and Olfactory Acuity. The Angle of Vision describes the width of the field of vision for a dinosaur. The greater the number the greater ‘peripheral vision’ the dinosaur has. Olfactory Acuity represents the dinosaur’s ‘sense of smell’. We know that some dinosaurs had large olfactory bulbs from casts of their brain cases.

It is widely understood that predators, like T. rex had stereoscopic vision, like humans but their field of vision was limited to about 20 degrees while prey animals, like Edmontosaurus had eyes set far apart on their heads which allowed for very wide fields of vision.

In this screen capture from the Dinosaur Island AI testbed program you can see a T. rex with narrow, 20 degree field of vision (shown by the blue lines) and two Edmontosaurus with much greater (120 degree) field of vision. Click to enlarge.

In the above screen capture you can see the difference in predator and prey fields of vision. This will have an important impact on the AI that governs prey stalking and herbivore defensive strategies. In our previous post (Calculating the ‘cone of stink’ for a T. rex) we demonstrated how a T. rex would have to maneuver downwind of its prey before beginning it’s final rush towards its victim. A herd of Edmontosaurus, however, had numbers on their side. More eyes scanning the terrain might well give advance notice of an impending predator attack.

In the next few weeks we will see the AI for both these attack and defense strategies implemented.

Following a comment from Paleontologist Dr. Jordan Mallon (below) with a link to the paper, “Binocular Vision in Theropod Dinosaurs” Stevens, Kent, Journal of Vertebrate Paleontology 26(2): 321-330 June 2006, we’ve modified the field of vision for the T. rex to 55 degrees and the Edmontosaurus to 145 degrees (see screen capture below).

Screen capture from the Dinosaur Island AI Testbed program showing a T. rex with a 55 degree field of vision stalking an Edmontosaurus with a 145 degree field of vision.

Specific information about the field of vision for hadrosaurs (like Edmontosaurus) does not appear to be available however, quotes such as, “The eyes were placed on the sides of the head which suggests that hadrosaurs were probably specialized for wide-field rather than for binocular vision,” definitely suggest a very wide field of vision.

Dinosaur Island is specifically designed to easily change values such as field of vision for a species.

# Calculating the ‘cone of stink’ for a T. rex

Calculating the direction and intensity of the smell from a T. rex. Note wind direction and speed at bottom. The red line is the direction that the T. Rex named Bob’s scent is being carried. Angle from Gertie to Bob is blue line. Screen capture from Dinosaur Island AI testbed (click to enlarge).

Yes, it has come to this: we are calculating the ‘cone of stink’ of a T. rex.

I’m working on not just the ‘combat models’ for Dinosaur Island see (“Creating a combat model for T. rex versus Edmontosaurus regalis“) but the AI that drives the decisions and actions of the dinosaurs as well. While creating the AI I realized that scent was probably as important as sight to any dinosaur that didn’t want to become dinner. At the same time, predators – successful predators – should take wind direction into consideration when planning their attacks and consequently maneuver to be downwind of their prey.

After watching a number of predator / prey scenarios in Dinosaur Island I became convinced that the T. rex didn’t just see an Edmontosaurus from 500 meters away and start charging towards it. I think the T. rex maneuvered into position (downwind) and only then ran at top speed when it was within 50 meters of the victim. I don’t think that a T. rex had energy to burn – and they sure burned a lot of energy running with all that weight at top speed – and even an unarmored prey like Edmontosaurus could pack a terrific wallop with its tail if it was forewarned.

As we shall see in the next few postings, dinosaur predators were not just big dumb brutes and scavengers.  For them to survive they had to plan their attacks in advance or be incredibly lucky. Also, we shall see how ‘olfactory acuity’ and ‘angle of vision’ played an important role in detecting predators before it was too late for big herbivores like Edmontosaurus and that the key to their survival involved group defensive tactics.

# Creating a combat model for T. rex versus Edmontosaurus regalis.

A T. rex (Bob) is attacking an Edmontosaurus (Julie) while its companions (Gertie & Muffie) flee (screen capture of the AI test bed program). Click to enlarge.

We are at the point in the development of the AI routines for the inhabitants of Dinosaur Island where it is time to make decisions about the combat models used to determine the resolution of hostile encounters. As shown in the screen capture of the Dinosaur Island AI testbed program (above), the simulation is placing the dinosaurs in various appropriate states such as: resting, eating, looking for food, looking for water, stalking prey, moving towards water, moving towards food, drinking, fighting and fleeing.

My first thought on the subject of modeling combat between T. rex and Edmontosaurus regalis, the first two resident species on the island, was that it would be handled similar to ‘melee combat’ models that I had previously used for my wargames.

Below is a page from the manual for UMS II: Nations at War explaining the 20 variable equation used to decide combat between tactical units.

The 20 variable equation used to calculate combat in our UMS II: Nations at War (1989). Scan from user’s manual. Click to enlarge.

I was envisioning something similar for Dinosaur Island until I happened to see this video (below) which includes a sequence (starting at 4:45) describing hypothetical Edmontosaurus and T. rex combat.

What I took away from the video was:

• Edmontosaurus regalis  is bigger than I thought. I understood the size mathematically and that they could easily grow up to 13 meters (~ 40 feet) but it wasn’t until I saw this video that it was put in perspective, “they were as big as a railroad car.” And, “they could look into a second story window.”
• The tail of an adult ‘bull’ Edmontosaurus regalis  was a formidable weapon.
• T. rex, like many predators, would have preferred to attack adolescent or sick animals rather than encounter a full-size, and potentially lethal, ‘bull’.
• The correct pronunciation is Ed-MONT-o-saur-us. I’ve been saying it wrong for the last six months!

While there is still debate about whether T. rex was a predator or a scavenger (“Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly sauropods, although some experts have suggested it was primarily a scavenger. The debate over Tyrannosaurus as apex predator or scavenger is among the longest running in paleontology.” – Wikipedia) we know of at least once case where a T. rex tooth was found in an Edmontosaurus tail that had healed from the attack (“T. rex Tooth Crown Found Embedded in an Edmontosaurus Tail – Predatory Behaviour?” “The healed bone growth indicates that the duck-billed dinosaur survived this encounter.  In February of this year, researchers from the University of Kansas and Florida reported on the discovery of evidence of a scar on fossilised skin tissue from just above the eye of an Edmontosaurus.  In a paper, published in “Cretaceous Research”, the scientists concluded that this too was evidence of an attack of a T. rex on an Edmontosaurus.”). From this we can conclude that:

• Sometimes T. rex did attack a living Edmontosaurus.
• Sometimes the Edmontosaurus survived the attack.

Furthermore, we know that some T. rex had suffered bone injuries during their lifetime (“An injury to the right shoulder region of Sue resulted in a damaged shoulder blade, a torn tendon in the right arm, and three broken ribs. This damage subsequently healed (though one rib healed into two separate pieces), indicating Sue survived the incident.” – Wikipedia) consistent with the type of damage that a 5 meter long tail (described as being “like a baseball bat,” in the above, video) could inflict.

In other words, combat between T. rex and Edmontosaurus regalis was not a foregone conclusion. Indeed, it was entirely possible that the Edmontosaurus could walk away unscathed while the T. rex could suffer some broken bones.

The AI for Dinosaur Island will reflect this. When deciding if the T. rex will attack the AI will have to analyze the T. rex‘s chances of victory and potential injuries (risk versus reward) considering the size of the T. rex, the age of the T. rex, the health of the T. rex, the size of the prey, the age of the prey and the health of the prey. And, when the two dinosaurs actually engage in combat the tactics employed by both will probably decide the outcome.

If the T. rex can sneak up on the Edmontosaurus until they are within 50 meters or less and then close the distance with a rush the advantage would certainly lie with the predator. If the Edmontosaurus has forewarning of the impending attack it would either attempt to flee or stand its ground and assume a defensive posture.

There is reason to believe that both Edmontosaurus and T. rex had well developed olfactory bulbs in their brains and smell was an important sense for both animals. We will add wind (and wind direction) to Dinosaur Island and incorporate this into the AI routines that control the dinosaurs. Predators will attempt to get ‘upwind’ of their prey; prey animals will ‘sniff’ the wind and respond if they smell a T. rex even if they can’t see it (see “Dinosaurs, tanks and line of sight algorithms” here).