Opened 22 years ago

Closed 20 years ago

#199 closed defect (fixed)

Raster map queries

Reported by: neteler@… Owned by: warmerdam
Priority: high Milestone:
Component: MapServer C Library Version: 4.1
Severity: normal Keywords:
Cc: mcilhagga@…

Description

Hi,

a long standing wish is the possibility of raster map queries.
We desire the possibility to query pixel values from displayed
raster maps.
It were great to have that implemented.

Daniel, just sitting besides me here at Trento, mentioned that
the display function and the raster file opening might need to 
be separated for this task.

The temporal solution to make vector polygons from a raster field
representation does not make too much sense....

Kind regards

 Markus Neteler

Change History (7)

comment:1 by fwarmerdam, 21 years ago

Status: newassigned
I would just like to add that Steve and I have discussed at some length now
how this would be done, and I indicated I would do it.  However, other pressing
matters have forstalled my work on this and I don't think it will be complete
for MapServer 3.7 release.

comment:2 by dmorissette, 21 years ago

Cc: steve.lime@… added
Owner: changed from sdlime to fwarmerdam
Status: assignednew
Version: 3.54.1
Reassigned to Frank as per comment #1.  Also setting version to 4.1 since there 
is no time for this in 4.0

comment:3 by fwarmerdam, 21 years ago

Status: newassigned

comment:4 by mcilhagga@…, 20 years ago

Frank, we may have some funding opportunities to get this completed. Any idea
how much work would be involved in providing raster query support? This would
have to be for GDAL sources.

We were talking here about some of the issues in dealing with raster querying
(ie. do you do the closest pixel to the point click, or take an average). For
this particular case, a closest pixel value would be perfectly acceptable.

Dave McIlhagga

comment:5 by mcilhagga@…, 20 years ago

Cc: mcilhagga@… added

comment:6 by fwarmerdam, 20 years ago

The basic capability would be not too hard.  However, when Steve and I 
talked about it we also considered some other possible addition ... basically
making mapserver more aware of information about the underlying rasters. I 
don't remember all the details of that, and can't seem to find the email 
where we discussed it now. 

The most obvious thing to implement would be returning the pixel value(s) at
the picked location.  However thing we also might want to consider:

 o interpolating values at pick location from 4 nearest pixel for 
   subpixel accuracy.
 o extracting pixel windows - pull a 3x3 window around pick point for instance.
 o extracting all pixels in a query box/polygon/etc - what kinds of constraints
   are supported for shape queries?
 o do we return scaled or unscaled values?  (presumably unscaled by default). 
 o do we have an option to return class name for classified rasters?


comment:7 by fwarmerdam, 20 years ago

Resolution: fixed
Status: assignedclosed
Raster queries are now essentially complete in the 4.3 source tree. 

Code in maprasterquery.c. 

See details at:

  http://mapserver.gis.umn.edu/cgi-bin/wiki.pl?RasterQuery
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