Re: Lat/Lon waypoints for GPS

Martin wrote:
On Sun, 6 Aug 2006 06:51:39 +0100, Keith <keith@xxxxxxxxxxxxxxxxxx>
wrote:

In message <fFTAwIBlzK1EFwB6@xxxxxxxxxxxxxxxxxx>, Keith
<keith@xxxxxxxxxxxxxxxxxx> writes
In message <jz1Bg.257$yG1.208@xxxxxxxxxxxxxxxxxxxx>, Dennis Pogson
<dennis_nospampogson@xxxxxxxxxxxx> writes

I just downloaded the full-size NASA MrSid image from
https://zulu.ssc.nasa.gov/mrsid/mrsid.pl There were no clouds on
this, and the image is startlingly clear and well-defined. The
earth map reference is N-49-20_2000 ( you have to keep zooming in
until the ref. numbers show, then click on Select Image and click
on the above sector in the map.

This will bring up a close-up window of the area and you can then
download the whole area (about 180MB). To view and use sections of
this you need the free MrSid viewer from LizardTech,
http://www.lizardtech.com/download/ which will enable you to
extract sections as tiff files and use them in various nav.
programs.

At full scale magnification and good eyesight you can see the
paddy fields (but not the rice shoots!) in Thailand.


Dennis, I've downloaded the viewer from LizadTech but I cannot find a
method of dowloading the specific area from MrSid.

OTOH I didn't download LizardTech, but did manage to view the area I
was interested in. The result was poor compared to Google Earth.

Google Earth uses thes images from NASA to compile it's own images, but then
adds aerial photography to certain city areas to allow zooming in to great
detail, (houses, cars people etc.)

Some of the images from the MrSid site are better than Google Earth, and
some are not. You have to zoom in to full (100%) magnification on the MrSid
viewer to get a true comparison. If Google Earth has cloudy images, these
can often be bettered by the MrSid images, but not always, you just have to
try both.

I never use these images for sailing navigation as I don't trust them as I
would a chart, and who wants to see a mass of blue water all the time? But I
do often label the maps using Ozi's "map comments" tool to identify specific
areas etc., which adds a little spice to navigating (you can dodge back and
forth between chart and photochart), and Ozi will overlay the Lat./Long onto
the photo, just as Google Earth does. By selecting portions of the
photograph for calibration in Ozi, and using the Print Scrn key, you can
also select the scale of the "chart". (I have some which show large portions
of the West of Scotland one one laptop screenful). If you use this method,
simply save the resultant file as a jpeg or png file.Very impressive.

Variety is the spice of life!

Dennis.




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