3d Line of Sight - Satellites

[ConorCahalane]

Hi All,

Im looking at the LOS tool in 3d Analyst, and I'm trying to see if there is a way of modelling an observer point, their environment (buildings etc) and GPS satellites in orbit top figure out if someone would have signal or would it be blocked.

I know it can be done, ive found at least three papers online by people did it. I have been experimenting in the office this morning but am a bit rusty on my ArcMAP. I have access to ArcMap 10 and 3d Analyst.

LOS seems to work with a line between observer and target? This seems a pretty time consuming way of doing it. If i have to draw a line between each point, i could just as easily tell then if they were blocked or not. From the LOS dialog box..

"The input lines should be simple, straight lines with only two vertices each, representing observer and target positions"


If i was trying to define a dynamic target, how should i go about it? Create a table with a an xyz representing each satellite position over a period of time? I would probably need to thin them down a bit, and if i included multiple satellites it would be quite computationally intensive...

This doesn't need to be perfect, just a proof of concept for my owen benefit. Any ideas about where to go would be appreciated.

PS - Somone told me recently avenue isnt used any more, what is used these days, python?

[AlexMahrou]

con20or, This seems like a really cool project.  Are you using the GPS almanac for your analysis?  In that case you are dealing with ECEF coordinates, which are unavailable in the ArcGIS environment.  You might need to translate them in terms of the coordinate system of your observer point on the ground. 

Tell me, are you performing some advanced GPS mission planning?

I created LOS between known control points and observed GPS point under canopy in a recent blog post.

[ConorCahalane]

Hi admahrou,

Interesting blog post, and im looking forward to reading part two in the urban canyons, its similar to what im doing in a way. Yes, it will be GPS planning, but for urban areas.

I had intended to get the details off the almanac, for GPS and Glonas at least. The transformation problem had occurred to me, but i hadnt thought it through properly,  the issue of z values was causing me a bit of bother, because they would be so hugem i dnt know if arc will model them!

What I had been planning was making a table with time as the primary key, and then xyz for each satellite. Then if you interactively picked apoint on a map, and a time, you could get LOS to satellites. Like I said, this has been done, but Im not sure how to go about using the LOS tool properly, and was hoping someone could help here. The current LOS tool seems VERY manual, and not easy to use with bulk data. For example in one of the papers I found, they wrote some avenue code

Count = 0
for each aTarget 'possible observable satellite
if (aTIN.LineOfSightsAsShapes (anObserver, aTarget,
ListOfShapes) = True) then
Count = Count + 1
end
end

Any suggestions?

[ConorCahalane]

had a change of mind today, im using 'observer points' instead and it seems to be working alot better.

[AlexMahrou]

Conor,

Have you seen the online Ashtec GPS Mission planner?  It allows you to visualize the time of day with Google Earth. 
http://asp.ashtech.com/wmp/

If you go through the steps, and then select "Smart 3d" for visualization, you'll get some pretty cool results.  The reason that I bring this up, is because you might attempt to get in touch with the programmers for this online app.  They might let you access the kml service or tell you how they got it done.

[ConorCahalane]

that is really excellent - and the 3d/google earth is great for illustration purposes