Right, I think there are two use cases:
1) data exploration - can be slower but needs flexibility
2) production serving - needs to be fast, and probably limits
flexibility to some predefined models
I think that there is also another angle to this, which is how the
summary data is computed for example:
1) min/max/average/std
2) statistical analysis
3) binning into some number of classes
4) removing outliers so the results are not skewed by them
5) etc
There are a lot of ways the people might need to summarize they data.
If the data is in a database, then you can add all the analysis, slicing
and dicing to the database and the rendering to mapserver.
So, I think that it would be nice to be able to read some "metadata"
about a layer and then use that for building the display using something
like colorramp and datarange. We might want to look at ways that we
could establish in mapserver for fetching the "metadata" about a layer.
For example:
1) define the "metadata" in the METADATA object
2) define a .met file for a shapefile or tileindex that contained the
"metadata" for that layer
3) define a separate SQL query that could be used to fetch the
"metadata" for the layer
4) something similar for other layer providers.
5) scan the data in two passes to compute some simple "metadata"
Thoughts?
-Steve W
Jan Hartmann wrote:
If you allow two passes, you can have all sorts of summarized values in
the template, to be used in the second pass, like Bart's actual extent
used for coloring. Doesn't look to difficult to implement to me, as long
as the two passes only get called when really necessary. I'm not sure if
performance is an issue for MapServer itself: if you really want high
performance, you should use the underlying format or database directly.
Jan
On 3-2-2010 17:02, Lime, Steve D (DNR) wrote:
How big a change would depend on the implementation. The brute force
approach where you simply loop through features once to compute ranges
and then again to draw would be probably pretty straight forward and
driver independent. Wouldn't be fast (but would be simple). Complexity
would be added as you try and boost performance by:
- allowing drivers to compute stats in their own way (e.g. add to
the layer API something like msLayerGetStats(...))
- caching geometries from a first pass through the shapes for the
second
Steve
BTW The color ramp support needs to be cleaned up first. I think we
scared the originator of that code away when an RFC was originally put
together.
-----Original Message-----
From: mapserver-users-boun...@lists.osgeo.org
[mailto:mapserver-users-boun...@lists.osgeo.org] On Behalf Of Bart van
den Eijnden
Sent: Wednesday, February 03, 2010 5:12 AM
To: mapserver-users@lists.osgeo.org
Subject: [mapserver-users] colorramp and datarange on the fly?
Hi list,
is it possible to have a colorramp in Mapserver based on the min and
max value in the current extent?
So instead of predefining the min and max in DATARANGE, have Mapserver
use the min and max value of the dataset in the current extent?
If not, would it be an easy change or a very complex one?
Best regards,
Bart_______________________________________________
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