[mapserver-dev] Vector field rendering

[Blaise Picinbono]

hi dear dev-list,

I am working at an oceanography lab and I have been asked to build a 
webmapping engine to display some data, such as ocean currents.
Most of the data are stored in netcdf files in a "vector field" format 
(U+V) (two rasters images).
I managed to display the netcdf files with mapserver, but as a raster 
image, only for 1 dimension at a time (U or V).

I am planning to convert the netcdf files in point shapefiles with one 
attribute for the angle and another one for the magnitude, but this will 
duplicate the data that are already very numerous and I am having hard 
times to find a nice symbolization of the point shapefile to display a 
thin arrow starting at every pixel center, with an angle, and a body 
length fixed by the U and V values.

Looking for some tricks in mapserver lists, I found the following thread 
on this dev list from late june, early july 2011 that seems to be 
precisely focused on this issue dealing with a very common way of 
storing winds and currents data in meteorology and oceanography.

As I am not following closely the latest developments of Mapserver, I 
would like to know if this issue is still discussed, or if it is under 
development and if I could try it by grabbing the CVS, or if it is 
already running in the latest stable release.

Thanks in advance,
Blaise




On 07/01/11 12:13, Jan Hartmann wrote:

Vector fields would certainly be very interesting for me. I use them

quite a lot when georeferencing old maps, to indicate the displacements 
between the originals and the (rubbersheeted) projected maps. It's not 
difficult to do with a PostGIS database, but a standalone MapServer 
facility would be quite welcome.

I'm not sure for how many people this would be useful. It really has 
great potential, but old maps are still mostly processed as archival 
documents, and the exciting possibilities of exact georeferencing are 
not fully recognized. A major reason for that is that they cannot be 
realized by predefined buttons in commercial GIS-systems. A more 
flexible instrument like MapServer is much more able to embed this sort 
of functionality. It's up to you whether it is worth the trouble to 
implement it; I would guess the demand from metereologists would be 
quite large too.

To give an impression of the possibilities for old maps, see the website 
for MapAnlyst:

http://mapanalyst.cartography.ch/

and Petr Pridal's web site on georeferencing old maps.

http://help.oldmapsonline.org/georeference



On 06/28/11 22:13, Daniel Morissette wrote:
>/ Hi Devs,
/>/
/>/ We've been asked about the possibility to add support for rendering 
/>/ vector fields in MapServer. I don't think that would be very 
/>/ complicated, but before answering I'd like to gauge interest from 
/>/ others in seeing this feature in MapServer.
/>/
/>/ Vector fields are used for instance in meteorology to store/display 
/>/ wind direction and magnitude. The source is two single-band raster 
/>/ images, one band represents the U component of the vector, and the 2nd 
/>/ band the V component.
/>/
/>/ Using the u,v values at a given location we can compute a rotation and 
/>/ magnitude and use that to draw an arrow of a size proportional to the 
/>/ magnitude and pointing in the direction of the phenomenon (wind, 
/>/ current, etc.)
/>/
/>/ Wikipedia has a nice figure showing what I'm talking about:
/>/
/>/   http://en.wikipedia.org/wiki/Vector_field
/>/
/>/ Would there be interest in seeing support for vector fields added to 
/>/ the MapServer core? Has anyone done work on that front already?
/>/
/>/ Daniel
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