[MLB-WIRELESS] Elevation maps on BrisMesh site

[Tim Hogard]

> 
> I don't know what we have behind the loc finder but I assume there is a 
> rdbms somewhere there. Rather than pre-draw the images we could 
> pre-calculate and then render the appropriate data sets.

The database just has lat/lon of very poor quality.

> Is anyone actively working on a countour hunting algo?
> Can we borrow the Brisbane one?

There are two types of data for elevation.  One is the old
survey data which is lines at specific elevations.  Depending
on the area and age it was done in feet or meters and a large
assorment of map datums.  The other data is the srtm data which
is roof/tree top data with a data point about every 90 meters.

All you need to do with the srtm data is fine the two points that
are at the end of the location and find the height of nearby grids
along the direct line and that should give you a good idea.  The
problem is that the strm data is all in WGS84 and all the coordinates
on the web site are mostly in one of the Aus map datums (mostly
66).  the problem with the map datums is that often a signle local
reference point will be used that was never properly surveyed so
you end up with local offsets.  The only way to use the srtm data
is have a map viewer were people can find their house using the
srtm data and that requires lots of funny shifts in the elevation
data to enhance the contrast.  If you look closely roads do show
up in the data.

-tim
http://web.abnormal.com

To unsubscribe: send mail to majordomo at wireless.org.au
with "unsubscribe melbwireless" in the body of the message