Xander,
You could have a look at using GDAL's virtual format (VRT) to point
to your original data and specify the nodata value in the VRT (you could
even get exotic by using TILEINDEXs of VRTS).
Another option is to instead use the PROCESSING "LUT=..." directive.
This may allow you to specify the target nodata value as well as the
source nodata value when you tweak the directive for each of your
elevation layers. But I haven't tried it...
Best Regards,
Brent Fraser
On 12/27/2011 9:04 AM, Enzmann, Alexander R. wrote:
Brent,
Thanks for the tips. Was able to make some progress.
A couple of quick notes on the source data - it is either text based (.asc) or
GeoTIFF. In either case, individual pixels are 16 bit signed values (meters).
The intended use is to use it as terrain (WMS access to terrain information in
.bil or .tif formats), not to generate colored images. So while GDAL is great
for turning the source uncompressed data into LZW compressed GeoTIFF files, the
tools for shading/coloring aren't useful in this application.
OFFSITE might work if I can figure out how to use it for a 16 bit signed value
instead of RGB. If I try something like this:
OFFSITE -9999
The parse fails. Using a color like this:
OFFSITE 0 0 0
Gives a useable result, pulling content from the coarse (SRTM30) terrain when
there are negative values in the higher resolution terrain. I suspect it works
for the wrong reason (e.g., negative values in the source data are mapped to
the color 0).
However, it isn't quite the right result. What I'm really looking for is the
ability to specify the value(s) where the source data has missing values
(typically -9999 or -32768) or a range of data to ignore (Google Earth Fusion
allows this) such as: -32768:-20000,-9999,0.
Xander
This is a nearly working .map file:
# Query that would pull a piece of the earth:
MAP
NAME "ASTER"
EXTENT -180 -90 180 90
SIZE 512 512
UNITS DD
IMAGETYPE bil
PROJECTION
"init=epsg:4326"
END
OUTPUTFORMAT
NAME "asc"
DRIVER "GDAL/AAIGrid"
MIMETYPE "application/asc"
EXTENSION "asc"
IMAGEMODE INT16
END
OUTPUTFORMAT
NAME "bil"
DRIVER "GDAL/EHdr"
MIMETYPE "image/bil"
EXTENSION "bil"
IMAGEMODE INT16
END
OUTPUTFORMAT
NAME "bil16"
DRIVER "GDAL/EHdr"
MIMETYPE "application/bil16"
EXTENSION "bil"
IMAGEMODE INT16
END
OUTPUTFORMAT
NAME "gtiff_16"
DRIVER "GDAL/GTiff"
MIMETYPE "image/tiff"
EXTENSION "tif"
IMAGEMODE INT16
END
WEB
IMAGEPATH "/tmp/"
IMAGEURL "/tmp/"
LOG "/tmp/srtm.err"
METADATA
wms_title "ASTER Terrain"
"ows_enable_request" "*"
END
END
#
# Coarse (30 ArcSecond) terrain. There is worldwide coverage, so this
# is good for areas uncovered by SRTM data, as well as for high
# scale values.
#
LAYER
NAME "aster"
TILEINDEX "SRTM30/bathmetry.shp"
TYPE RASTER
STATUS ON
METADATA
"wms_title" "SRTM 30 ArcSecond Bathmetry"
"wms_group_title" "aster"
"wms_srs" "epsg:4326"
"wms_style" "Default"
"wms_extent" "-180 -90 180 90"
END
MAXSCALEDENOM 1000000000
MINSCALEDENOM 1
END
#
# Moderate resolution (1 ArcSecond) terrain. Coverage is available worldwide
# for most land areas between latitudes -80 and +80.
#
LAYER
NAME "aster"
TILEINDEX "/mcgi/Terrain/asterz.shp"
TYPE RASTER
PROCESSING "RESAMPLE=BICUBIC"
STATUS ON
METADATA
"wms_title" "ASTER 1 ArcSecond Terrain"
"wms_group_title" "aster"
"wms_srs" "epsg:4326"
"wms_style" "Default"
"wms_extent" "-180 -80 180 80"
END
MAXSCALEDENOM 1000000
OFFSITE 0 0 0
END
END
-----Original Message-----
From: Brent Fraser [mailto:[email protected]]
Sent: Friday, December 23, 2011 9:01 PM
To: Enzmann, Alexander R.
Cc: [email protected]
Subject: Re: [mapserver-users] Multi-Resolution Terrain Map File
You could use the OFFSITE value in the higher resolution layer.
Basically in this scheme, mapserver would render each layer, and any
place with an OFFSITE value would show the value from the layer under
it.
A more basic problem is how do you want the elevation value to be
rendered to a visible image? You could use GDAL to pre-process the
SRTM DEMs (http://www.perrygeo.net/wordpress/?p=7), or use mapserver to
classify the DEM values to colors on the fly.
Best Regards,
Brent Fraser
How do I construct a map file that can handle different resolutions of
terrain, with fallback to lower resolution when a no-value is found? In
Google Earth Fusion, I can specify multiple terrain sources and tell it
which value(s) represent missing data, and it will then process the
terrain, checking for availability of each type of terrain, falling back
if there isn't any in a geographic area and falling back if there is
missing data.
For simple fallback based on area coverage, I can use a map file like the
one below (using 30 Arcsecond SRTM and 1 Arcsecond DTED). Now, what would
I need to do to have it use/interpolate data from the 30 Arcsecond values
when there is a missing data/NODATA/hole in the DTED? In the file below,
gdaltindex has been used to generate the coverage shapefiles.
The example below is a simple one, and it would be really helpful to be
able to have multiple terrain sources and a way to automatically fill
voids the same way that transparency works with raster image layers.
Specifying that terrain values are posts and not pixels would be good too,
but lower priority.
Xander
_______________________________________________
mapserver-users mailing list
[email protected]
http://lists.osgeo.org/mailman/listinfo/mapserver-users
