Topic: EPSG4326->EPSG3857 Formula

[snownut2]

Ok I'm stumped,

Trying to convert a formula from "C" to lisp.  The formula converts coordinates in Google EPSG4326 (WGS 84) to NOAA Data Viewer coordinates EPSG3857 (WGS 84).

The resultant points will be used to define an AOI (Area Of Interest) window.  So they can be a "little off".

Below is what I've got so far, the 2nd to last line is the culprit, I know nothing about "C" programing.

Any assistance in getting this line right would be great.

Code - Auto/Visual Lisp: [Select]

1.  (defun EPSG4326->EPSG3857  ( vertex / smRadius smRange smLonToX smRadiansOverDegrees  vertex1  vertex2 y tan)
2.  
3.     (defun tan (x) (if (equal (cos x) 0.0 1.0e-16) (if (minusp x) -1.0e200 1.0e200) (/ (sin x) (cos x))))
4.  
5.     (setq
6.       smRadius  6378136.98
7.       smRange  (* smRadius  pi     2.0)
8.       smLonToX (/ smRange        360.0)
9.       smRadiansOverDegrees (/ pi 180.0)
10.       vertex1  (*(car  vertex) smLonToX)
11.       y          (cadr vertex)
12.     )
13.     (cond
14.       ((> y  86.0)
15.         (setq vertex2  smRange)
16.       )
17.       ((< y  -86.0)
18.         (setq vertex2  -smRange)
19.       )
20.       (T
21.         (setq
22.           y (* y  smRadiansOverDegrees)
23.           y (log  (+ (tan y) (/ 1.0 (cos y))))
24.           vertex2 (* y  smRadius)
25.         )
26.       )
27.     )
28.     (list vertex1 vertex2)
29.   );defun
30.  

"C" Code -     y = Math.Log(Math.Tan(y) + (1.0 / Math.Cos(y)), Math.E);

This  (setq test  (EPSG4326->EPSG3857 (list -72.5 42.6)))

Should return this - (-8070663.08251234 5251284.60483522)

edit - This is now solved, posted code works fine.....

Thanks,

Bruce

[dgpuertas]

Mayby change

Code: [Select]

(log  (+ (vle-tan y) (/ 1.0 (cos y))(exp 1)))
to

Code: [Select]

(log  (+ (tan y) (/ 1.0 (cos y))(exp 1)))

And define:

Code: [Select]

(defun tan (x / co)
(if (zerop (setq co (cos x)))
   1.79e308  ;Infinit
(/ (sin x) co)))

[Dlanor]

Code - Auto/Visual Lisp: [Select]

1. (setq y (log  (+ (tan y) (/ 1.0 (cos y))))
2. ;where
3. (defun tan (x) (if (equal (cos x) 0.0 1.0e-16) (if (minusp x) -1.0e200 1.0e200) (/ (sin x) (cos x))))
4.  

my "C" is very rusty, not used it for +20 years, but log in autolisp deals with natural logs and I don't  think you need the (exp 1) which as the memory dims is the base for the Math.Log

[snownut2]

Thanks,

Dlanor that works perfectly, BricsCad has the vle-tan function so there is no need on my end to construct a tan function.

I will post it in the original code so it is useable for ACAD user. 

This transformation function will allow users to call the NOAA Data Access Viewer site and open at their AOI window. 

I am using it to assist the users in locating LIDAR data for later use.

Bruce

[Dlanor]

No problem