Re: [Matplotlib-users] Analyzing unprojected (spherical, geodetic) vector data and Matplotlib

[Zane S. <za...@id...>]

Well, the translation/rotation on a sphere is just a kind of wish-list 
thing... but it would be awfully nice.  It seems like someone must have 
done that, for re-drawing continental outlines as they drift across the 
surface of the earth over time or something.

What I do need, for instance, is to be able to build up a polyline 
object given a starting (lat,lon), an azimuth, and a distance to go.  Like:

start at (lat0,lon0)
go 10km at a heading (calculated based on my location and time)
what is my new (lat,lon)?
Calculate a new heading (based on my new location and time)
go another 10km along that heading.
etc.
etc.

saving each of the (lat,lon) points that I stop at, every X km along the 
way.

It needs to work even if I go near a pole, or across the "wrap-around" 
point in Longitude.

Then I need to be able to take that lineament (list of lat,lon points) 
and compare its shape to the great circle which best fits its overall 
trajectory, e.g. distance to the best-fit great circle from the 
lineament as a function of distance along the lineament.

I want to be able to generate statistically similar synthetic 
lineaments, based on a mapped lineament, like, lineaments that have a 
similar power spectrum (compared to their best fit great circle), but a 
different overall shape, or orientation.

And I need to be able to calculate the points at which different 
lineaments intersect, and the ordering of the intersections along 
lineaments... I.e. the lineament object needs to be able to answer the 
question, given a set of other lineament obejcts, "who do I intersect 
with, and in what order, and how far along me is each of those 
intersections?"

It's only at the very end that I need to be able to take one of these 
polylines and send it to the map for visualization.  Mostly I need to be 
able to analyze it.

Thanks for any suggestions on packages to look at.

I should dig deeper into Basemap to see what all it does.

Zane

Jeff Whitaker wrote:
> Zane Selvans wrote:
>> Hello all,
>>
>> I need to do analysis of vector data (linear features, polylines) on 
>> the surface of a sphere.  Many of the lines span a significant portion 
>> of the circumferance of the the body in question (Jupiter's moon 
>> Europa), and I want to be able to do the display of the data and 
>> analysis within Matplotlib.
>>
>> Rather than writing my own (probably lame) module for manipulating and 
>> generating linear features stored as lists of (lat,lon) points, I'd 
>> prefer to build on someone else's work.
>>
>> After a little searching around, it seems like most open GIS packages 
>> (e.g. OGL, GDAL) seem to work exclusively within a projected planar 
>> space.  Am I missing something?  Is there anyone else out there that 
>> does this kind of thing?  What solutions do people have that work well 
>> with Matplotlib and the Basemap toolkit?
>>
>> Ideally, I'd like to have the ability to perform transformations on 
>> the polylines, rotating and translating them on the surface of the 
>> sphere (without having to do the spherical trig myself), and I have to 
>> be able to have features cross the "date line" and wrap-around 
>> intelligently, calculate great-circle distances (and forward/back 
>> azimuths), best-fit great circles, etc.
>>
>> Thanks for any recommendations you might have,
>> Zane
>>
> 
> Zane:  Basemap can calculate great-circle distances (with forward/back 
> azimuths).  I'm not to clear on the types of transformations you need, 
> but Basemap basically just does the forward and inverse transformations 
> from map projection to geographic (lat/lon) coordinates.  My guess is 
> that it won't do the type of rotation and translation that you want to do.
> 
> -Jeff
> 


-- 
Zane Selvans
Amateur Human
za...@id...
303/815-6866
PGP Key: 55E0815F