Re: Using 0.75 arcsecond CDED data??

Ingrid and Kris wrote:

> I've finally managed to get Terragear to compile on my Linux machine, 
> and have been trying to generate some scenery based on the Canadian 
> 0.75 arcsecond DTED data available (free) from www.geobase.ca 
> <http://www.geobase.ca> . I've been running into some problems though. 
> It seems to pass the Demchop stage, but I'm not sure if it does so 
> correctly. I skipped the vmpa0 and airport data steps (I just want to 
> see if my DTED data works), does skipping these steps prevent you from 
> getting output? At any rate, here is the results of the 
> fgfs-tools-client program:
>  
> Output directory is .
> Working directory is .
> Tile id is 1712603
> Center longitude is -110.664
> Center latitude is 33.3529
> X distance is -1
> Y distance is -1
> Load directory: ./Dem-.75
> result of setting mem limit = 0
> Building tile 1712603
> Construct tile, bucket = -76:3, 45:3
> array_path = ./Dem-.75/w080n40/w076n45/1712603
> Opening array data file: ./Dem-.75/w080n40/w076n45/1712603.arr.gz
> Opening fitted data file: ./Dem-.75/w080n40/w076n45/1712603.fit.gz
> Found Array file ./Dem-.75/w080n40/w076n45/1712603
> origin = -270900 163350
> cols = 1201 rows = 601
> col_step = 0 row_step = 0
> Done parsing
> poly_path = ./Dem-.75/w080n40/w076n45
> 1712603.arr.gz 1712603 'arr.gz'
> 1712603.fit.gz 1712603 'fit.gz'
> loaded 0 total polys
> clipping polygons
> Running master clipper
> (-75.25,45.375) (-75,45.5)
>  
>  
> The end result of this is no file (tile) is created. One thing that's 
> really odd is that it says that the Center longitude is -110.664 and 
> latitude is 33.3529....but I'm building around -76.00 long and 45 lat. 
> The other thing that seems odd is that X distance and Y distance are 
> listed as -1. Additionally, col_step and row_step are listed as 0. Is 
> this a problem with the 0.75 arcsecond format (truncation to int perhaps)?
>  


Kris,

Ignore the "center lon/lat" message at the beginning.  You can specify a 
tile id to build (and if you don't, you can specify the tile by lon/lat 
which is what this message is relating to.)  Basically the lon/lat which 
defaults to the values shown is ignored if you specify a tile id.

Here's what I suspect is going on.  Tiles are a collection of 2d data 
that is first clipped and prioritized.  Then this 2d data is, elevated 
based on the SRTM/DEM data.  If there are no 2d polygons defined for 
your tile, you will end up with nothing.

One thing that vmap0 provides is basic landmass outlines, so that is 
most likely what you are missing.

Regards,

Curt.

-- 
Curtis Olson        http://www.flightgear.org/~curt
HumanFIRST Program  http://www.humanfirst.umn.edu/
FlightGear Project  http://www.flightgear.org
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