[Geomoose-users] Geomoose 2 and custom footer data readouts

[Brent Fraser]

Johan,

     Interesting stuff; could be difficult to get good performance though.  And 
it will take some coding effort.

     GeoMoose's coordinate readout for projected coordinates works fast because 
there is a simple linear (scale and offset) relationship between the current 
cursor location in pixels and the projected coordinates (in say feet or meters). 
  The readout display of Lat/Lon works fast because the map projection formulas 
have been written in JavaScript and get loaded into the browser.  These formulas 
do the heavy lifting of converting projected coordinates to Lat/Lon.

Elevation is a different story.   Each value is potentially unique at any 
location (there is no formula). And while there are ways on the server to 
color-code a raster DEM as an image or contour it as lines, there are no 
facilities (that I know of) to display the elevation directly in a web mapping 
environment.

Here are a few options:

1. Write an elevation server.
     On a mouse move event, have GeoMoose issue a CGI query with the current 
Lat/Lon values.  The CGI service would access the elevation datasets (using 
GDAL's API?) and return a little XML with the elevation value.  GeoMoose would 
then display the value in the status bar with the other coordinates.  And this 
would happen on every mouse move.  Performance could suck, but with using 
fast-cgi maybe not.

     I like this option since it could solve my problem of displaying 
Township/Range numbers on the fly...

2. Extend GeoMoose to be a WCS client
     Add JavaScript to GeoMoose to get an OGC Web Coverage Service raster (e.g. 
a DEM) on every pan and zoom.  GeoMoose would then do the elevation look-up on 
the client side on every mouse move (but no need to hit the server).  Likely 
much better performance than 1. above, but you'd need to find a WCS server (can 
Mapserver do that now?).

In any case, the data management of the DEMs is done on the Elevation/WCS server 
and if it is done right it won't matter how may meg/gig/tera bytes you have.


BTW, some other ideas I had on my Township/Range value display: use imagemaps or 
a GML polygon layer with attributes, then have GeoMoose display the attribute 
value in the status bar.

Best Regards,
Brent Fraser
GeoAnalytic Inc

Johan Forsman wrote:
> Hello All:
> 
> I have an idea to improve our mapserver product, and I come to you asking for help formulating an approach to realizing it.
> 
> What I want to attempt is a seamless, continuous readout of elevation data in the Geomoose footer, next to the coordinate-display and scale-jumper features.
> 
> I have access to elevation data in the form of USGS DEM rasters, either from 1:24000 quads or from a much denser (and far larger) LIDAR dataset. The quad DEM dataset consists of just under 1000 quads, in what appears to be 16-bit signed integer format, 
> each file with a unique name equal to the USGS quad code. Files appear to be 1-2 megs in size on disk.
> 
> The LIDAR dataset appears to use a 32-bit float format, there are over 3500 individual files with unique names that do not correspond directly to the USGS quarter-quad code (but I can possibly generate a lookup table for the translation). Alternatively 
> the LIDAR data is available as CSV format. Files are quite large, 10-12 megs for the rasters and 150 megs for the CSVs. Each.
> 
> I am not (yet) interested in displaying the data as an image, only returning the point values at any given location in the footer, and also in the results header when a user clicks on a spot with the identify tool.
> 
> How should I (can I? do I need to?) approach crafting a mapserver file that points to 3500+ individual rasters?
> 
> Where is the integration point with the footer in Geomoose2? Does the function currently exists to return the type of data I want to display?
> 
> Am I thinking all wrong about this? This is very likely.
> 
> Should I just forget about the whole thing? Can it even be done?
> 
> Please opine at will on this subject.
> 
> Thanks!
> /Johan.
> 
> ----------------------
> Johan Forsman
> Geologist
> Safe Drinking Water Program
> Louisiana Department of Health and Hospitals
> Office of Public Health
> Telephone: 225.342.7309
> Telefax: 225.342.7303
> 
> 
> 
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