Re: [racket-users] HtDP2e, exercise 5

[Fernando Basso]

On Sunday, August 13, 2017 at 9:28:50 AM UTC-3, Jens Axel Søgaard wrote:
> 2017-08-13 13:21 GMT+02:00 Fernando Basso :
> The description of the problem is:
> 
> 
> 
> “Use the image primitives to create the image of a simple automobile, boat, 
> or tree. Make sure you can easily change the scale of the entire image.”
> 
> 
> 
> What sort of math am I supposed to know in order to apply this concept of 
> "scaling" the image?
> 
> 
> 
> Perhaps something like:
> 
> 
> 
> (define SIZE 200)
> 
> (define car-body (rectangle (* SIZE 1) (* SIZE 0.4) "solid" "orangered"))
> 
> (define tire (circle (* SIZE 0.1) "solid" "black"))
> 
> 
> 
> I think if I do something like that I can then later change SIZE and 
> everything should still work fine.
> 
> 
> 
> Is that the expected approach or I am missing some other math concept here?
> 
> 
> 
> Basically, but it is a clearer if you make the scale explicit.
> 
> 
> Something like this:
> 
> 
>     (define scale 2)
>     (define TIRE-RADIUS  (* scale 10))
>     (define CAR-LENGTH (* scale 90))
>     (define CAR-HEIGHT  (* scale 40))
>     ... draw car ...
> 
> -- 
> 
> Jens Axel Søgaard

All right. Thanks a lot for your time and explanation. Much appreciated.

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Re: [racket-users] HtDP2e, exercise 5

[Jens Axel Søgaard]

2017-08-13 13:21 GMT+02:00 Fernando Basso :

> The description of the problem is:
>
> “Use the image primitives to create the image of a simple automobile,
> boat, or tree. Make sure you can easily change the scale of the entire
> image.”
>
> What sort of math am I supposed to know in order to apply this concept of
> "scaling" the image?
>
> Perhaps something like:
>
> (define SIZE 200)
> (define car-body (rectangle (* SIZE 1) (* SIZE 0.4) "solid" "orangered"))
> (define tire (circle (* SIZE 0.1) "solid" "black"))
>
> I think if I do something like that I can then later change SIZE and
> everything should still work fine.
>
> Is that the expected approach or I am missing some other math concept here?
>

Basically, but it is a clearer if you make the scale explicit.

Something like this:

(define scale 2)
(define TIRE-RADIUS  (* scale 10))
(define CAR-LENGTH (* scale 90))
(define CAR-HEIGHT  (* scale 40))
... draw car ...

-- 
Jens Axel Søgaard

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