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Re: [pygame] how to "think rotation" on a longitude-latitude reference system ?

Hi Massimo,

You may find the quaternions in pyeuler useful:

http://code.google.com/p/pyeuclid/
I'm not sure, but I think using that terminology, if you have a quaternion representing your position/orientation on the surface of the sphere, then converting it to euler angles gives your (longitude, latitude, heading) = their (heading, attitude, bank). Your motion routines should all be straightforward: convert each of your directions to quaternions, and then multiply. 

You will end up with something like

current_pos = Quat()

frwd = Quaternion.new_rotate_euler(...)
left = Quaternion.new_rotate_euler(...)
rot  = Quaternion.new_rotate_euler(...)

while True:
 # to move forward
 current_pos *= frwd

 # to move back
 current_pos /= back

 # similarly for others

 (long, lat, head) = current_pos.get_euler()
The details are probably a little off (I'm a little rusty on quats myself, and it depends on the conventions you use), but I think that's the gist of it. The link in the source for pyeuler (http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToEuler/index.htm) seems useful. 

--Mike

Massimo Di Stefano wrote:

Hi All,
" i'm not expert programmer, just a biologist student :-/ with self-teached python experience 
so apologize my questions if they are based on wrong assumptions "
for my study i need to write a code to inteface a joystick device with an open source application similar to google earth. 

this application is a 3d globe based on openscenegraphic (OSG),
it has a "tcp listner interface" that accept xml message to move a camera-view around the globe 

the message to move the globe is something like :

go_to_lat_lon(latitude longitude roll picth head)
i tried to code in python using pygame, the results is (my fault) an "ugly" code that is not able to update the position according with heading changes (view direction).
exactly i have a 3 axis joystick 
axis_x -> +/- longitude
axis_y -> +/- latitude
axis_z -> +/- 0-360° (heading)
axis_v = 0-1 (speed)
the code i wrote use the axis_x and axis_y to change longitude and latitude and axis_z to change the view direction.
but it is totally wrong beacouse if i have heading = 0 = 360 (e.g. look to north) the code works as aspected ... but if i change direction (view turns) the axis code is not update. so if i look yo east and put the joysrick up (go ahead) it don't go to east .. but go ever to north. 

move the axis_y up move the planet to north
move the axis_y down move the planet to south
move axis_y left and right move the planet to west and east
but beacouse my code is totally separated by the heading changes, if i change heading the joystik x/y axis action is immutate.
this beacouse i connect the x/y action to a code that simply do an increase/decrease lon-lat values.
increase : 
for i in arange(j , j+1):
lati = [sum(zlat)]
a = abs(axis_v) * abs(axis_x)
lati.insert( i+1,a )
zlat = array(lati)
lat = sum(zlat) j = 0.1 

for i in arange(j , j+1):
lati = [sum(zlat)]
a = abs(axis_v) * abs(axis_x)
lati = [sum(lati) - a]
zlat = array(lati)
lat = sum(zlat)
j = 0.1
i used the increase decrease code to handle all the avaiable condition, North, South, East, Ovest, Ne, Nw , Se , Sw : 

1)

axis_x < 0
axis_y == 0

2)

axis_x == 0
axis_y > 0

3)

axis_x > 0
axis_y == 0

4)

axis_x == 0
axis_y < 0

5)

axis_x < 0
axis_y > 0

6)

axis_x > 0
axis_y > 0

7)

axis_x > 0
axis_y < 0

8)

axis_x < 0
axis_y < 0
i hope exists already a function in opengl that can help me to solve this problem reading a lot on google seems my problem can be solved using complex math like quaternion 
or rotation around an arbitrary axis.
i can ignore roll and pich, beacouse i can chenge them using the joystick hat .. an roll and pich are ininfluent on the lon-lat position ... while the heading is strictly related to the position beacouse it represent the movment direction. 

plese apologize again my ugly code, this what i'm actually using :

http://www.geofemengineering.it/data/epi_joy.py

this the results :

http://www.geofemengineering.it/Site/Media/ossimplanet_joystick-2.mp4
while here i tried to learn quaternion .. but my brain is not hable "yet" to undstand how to works with quaternion in a "longitude - latitude" space :-( 

http://www.geofemengineering.it/data/epiquath.py

i hope some one can help me!
please i'm italian so it is a bit hard to find the right word to describe my problem for eny more detailed explanaton, please ask me where i need to give more precise informations. 

thanks to help me!

ciao,

Massimo.