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Relative Speed Of Cars Driven By The Ai


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#1 mcmirande

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Posted Jun 23 2020 - 06:56 PM

Hello everybody

I was comparing how different cars (of the original GPL cars, at least by now) behave when driven by the AI. I tested it in different tracks after copying the Jim Clark "AI" to all drivers and reducing all that I could the random features of the AI, as suggested by Lee Bowden in his AI tutorial.  Following him, I also reduced the number of drivers to allow them to drive with free track.  I left only one car of each brand and put them to qualify for one hour (obviously with accelerated time).

Well, my main and original question was if is there something of the track layouts that GPL takes into account to, together with features of the chassis, "calculate" how quick every car will be.  This seemed to be that way, according to this table (for some tracks only)

See figure


The numbers are seconds slower that each car will be relative to the fastest car for each track in a race of 45 minutes. As you may see, in Rafaela and Avus, the AI Eagle is faster than the Lotus, and numbers of the table in general seem reasonable.

However, there are some numbers that are strange for me. For instance in Reims the AI Lotus is (marginally) faster than the Eagle and in Balcarce and The Moon (not listed here), the  BRM is much slower than the Honda and Cooper.

So, my questions remain the same.  Does somebody know what determines the relative speed of each AI car on every track? Is there something beyond the features of each car and (I guess) some data from the .lp files determining the speed of each car?  (here I note that the .lp files are from just one car and that relative laptimes at Alta Gracia are reasonable even with my rudimentary .lp files).

Well, thanks for any clue.  And I'm sorry if it was discussed in some other thread (that I didn't found).

Cheers, Marcos.

Attached Files


Edited by mcmirande, Jun 23 2020 - 09:26 PM.


#2 jgf

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Posted Jun 23 2020 - 07:32 PM

I believe there is a certain random factor, possibly hardcoded, so the same driver in the same car at the same track will not always do the same lap.  But more importantly we must also consider the lp files at any particular track cannot be optimum for all cars;  were they designed for a particular car?  or a compromise to work equally poorly for each?  So the lp files at one track may work better for the BRM while those at another track may be better for the Eagle.  The lp files do not apply to us so we, as human drivers, adapt our driving to a particular car and track, but the AI follow the same line with the same "braking points" and the same "acceleration" regardless of what car they have.  For the same reason some mods may work better than others at some tracks.

#3 Lee200

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Posted Jun 24 2020 - 09:27 AM

The speeds listed in the track .lp file certainly affect the AI.  I've always thought of them as being speed goals that the AI will attempt to attain providing there isn't something else that limits them.  The AI use the same engine code as the player so acceleration is limited by whatever engine the AI car has.  If the AI car engine is weaker than the car engine used to produce the .lp file, then the AI won't be able to achieve the .lp speeds.

Cornering speed is handled differently and all AI cars will corner about the same given the same driver.

One of GPL's limitations is that AI corner speed will be too fast if the driver settings are set so that the AI car will achieve the same max speed as the player.  My AI Speed Control patch tires to overcome this.  It artificially lowers the .lp corner speed so that a higher driver hype setting can be used to achieve the proper max speed.

http://gplmotorworks...ol Patch v2.zip

#4 jgf

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Posted Jun 24 2020 - 10:54 AM

I've never tweaked GPL lp files, but from all I've read they work the same as in other Sierra sims ...except GPL has to contend with several different physics models while Nascar sims only had one.  So the lp files will have to be a compromise;  set straight line speeds for the fastest car and all the others will attempt to achieve those speeds with their power, grip, and drag, which is realistic;  but what to do about cornering?  the fastest car is certainly not the best handling, set cornering speeds for it and the best handling cars will now be limited in their abilities, set cornering speeds for the best handling car and the fastest car will probably be spinning too often as it tries to achieve those speeds.  Does GPL address this some way internally (hardcoded) or just use compromised cornering speeds in the lp files (fastest car doesn't corner as slowly as it should, best handling cars don't corner as fast as they should).

#5 mcmirande

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Posted Jun 24 2020 - 12:12 PM

Thanks for the answers and comments!

So, maybe in Reims both the Lotus and Eagle are reaching the fastest .lp speed, but the Lotus has better acceleration from the hairpins. That would explain Reims, according to the data from Lee.  Different laptimes for each car in each track, thus, would be probably related to the proportional time in the lap going straight, given that cornering is about the same speed for all cars.  That would also explain the slight difference between chassis in Ahvenisto, in which cars are cornering most of the time.

I could understand that in Balcarce, which is full of braking and accelerating to/from very slow speeds, and relatively long full throttle sections, is especially difficult for the BRM.  But still The Moon upsets me.  In that track the Cooper and Honda ran almost 10 seconds faster than the BRM...

Do AI cars use some kind of "setup"?  I mean, default setups should influence AI laptimes?

Thanks for the feedback!  Marcos.

Edited by mcmirande, Jun 24 2020 - 12:13 PM.


#6 Lee200

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Posted Jun 24 2020 - 03:11 PM

Player setups have no effect on the AI.

#7 mcmirande

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Posted Jun 24 2020 - 05:04 PM

Ok, thanks Lee

#8 jgf

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Posted Jun 25 2020 - 02:35 PM

AI performance is based on a combination of the physics of the car they are driving, their parameters in the player.ini file, and the mapped speeds in the lp files.  But they have no "setups".

#9 mcmirande

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Posted Jun 25 2020 - 11:18 PM

Thanks jgf :)




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