[Xastir] Ridge Radar images

[Rick Green]

Please take my previous message with a grain of salt.  When I zoom out to 
a wider view, I see the apparent circle of coverage for the radar is 
displaying as an ellipse, and the values I entered for the second tiepoint 
don't correspond to the apparent lower-right corner of a rectangle 
enclosing the ellipse, and the center of this ellipse is well east of 
White Lake, MI, where the radar is located.
   So my calculations  are still off.  I need help after all.  Is maybe the 
'map units' referred to in line1 and line4, NOT decimal degrees?  If not, 
what are they, and how do I calculate a second tiepoint from them?

Rick, N8BJX


On Fri, 25 Dec 2009, Rick Green wrote:

> I, too have sorely missed the WMSRadar images, so I was excited to see the 
> link to the RIDGE data discussed here a week or so ago.
>  I dove in and re-read README.maps, as well as the web pages referenced in 
> that thread.  I created the following .geo file for the Detroit RIDGE radar, 
> placed it in my maps directory, reindexed all maps, and selected it in the 
> map chooser.  No joy, I see no radar data displayed.
>
>  So I began to compose this email to ask for some help.  In the process, I 
> retraced the steps I took, so I could document them, and discovered the 
> arithmetic error in my latitude calculation.  Doh!
>
> Since I'd already typed in my step-by-step, I decided to send this email 
> anyway, not as a request for help, but as a HOWTO and example for others.
>
>
> Each of the RIDGE radar image has a "world file" associated with it. A world 
> file is an ASCII text file associated with an image and contains the 
> following lines:
> Line 1: x-dimension of a pixel in map units
> Line 2: rotation parameter
> Line 3: rotation parameter
> Line 4: NEGATIVE of y-dimension of a pixel in map units
> Line 5: x-coordinate of center of upper left pixel
> Line 6: y-coordinate of center of upper left pixel
>
> Here's the .gfw file I found corresponding to the image I selected:
>
> 0.00978707053444604
> 0.000000
> 0.000000
> -0.00978707053444604
> -86.4032277471369
> 45.3865516246449
>
> I downloaded the .gif file, saved it, and used gwenview to open it and 
> examine its properties, to learn its size, from that, I generated the 
> IMAGESIZE line.
> the first TIEPOINT line is generated directly from lines 5 & 6 of the .gfw 
> file.
> The second TIEPOINT line was generated by multiplying lines 1 and 4 by the 
> corresponding size parameter, and subtracting from corresponding line 5 or 6 
> value.
>
> Longitude = line5 - (line1 * 600) Latitude = line6 + (line4 * 550)
>
> Here's the complete geo I generated:
>
> #RidgeDTX.geo
> # Base reflectivity from Detroit (white Lake) RIDGE radar
> #Label		X	Y	Long		Lat
> URL	http://radar.weather.gov/ridge/RadarImg/N0R/DTX_N0R_0.gif
> TIEPOINT	0	0	-86.40322	45.38655 TIEPOINT	599 
> 549	-80.53098	40.00366
> IMAGESIZE	600	550 REFRESH 120
> TRANSPARENT 0x0
>
> I placed this above TIGERMAP.geo, and below WORLDHI.map, and I now have a 
> radar image overalyed on my xastir display.
>
>
> -- Rick Green
>
> "Those who would give up essential Liberty, to purchase a little
> temporary Safety, deserve neither Liberty nor Safety."
>                                  -Benjamin Franklin
>
> "As for our common defense, we reject as false the choice between our
> safety and our ideals."
>                               -President Barack Obama 20 Jan 2009
>

-- 
Rick Green

"Those who would give up essential Liberty, to purchase a little
temporary Safety, deserve neither Liberty nor Safety."
                                   -Benjamin Franklin

"As for our common defense, we reject as false the choice between our
safety and our ideals."
                                -President Barack Obama 20 Jan 2009