[Mapserver-dev] Fwd: MapServer testing results

[Howard Butler]

Paul,

 From the ArcSDE C API documentation:
>SE_layerinfo_get_envelope returns the user-defined envelope of a specific 
>layer. This envelope is not necessarily the 'true' calculated envelope of 
>the layer's features

My guess is that this is the extent of the layer that is given when the 
layer is loaded. Some of the ArcSDE loading tools loop through each polygon 
and calculate a full extent, but it varies by tool (cov2sde,shp2sde, 
ArcCatalog, etc).  This extent is put in a table and stuffed in the 
SDE.LAYERS table as minx, miny, maxx, maxy.  I believe these are the values 
that are returned by SE_layeinfo_get_envelope.

You choose the indexing method when you specify a "keyword" in the 
dbtune.sde file on the server.  (everything is usually just loaded with the 
DEFAULT keyword, depends on how SDE was setup and how the data were 
loaded). You can adjust the index and update statistics using the sde 
command-line tools, but as far as I know, it should be indexed in some 
capacity when you load it.

So to answer your question, yes the call to SE_layerinfo_get_envelope is 
cheap.  It's just that its answer sometimes sucks.

The real work is done here though.  The rectangle from 
SE_layerinfo_get_envelope is then crossed against the given rectObj (in 
most cases just the mapObj's extent).  The resulting shape is then used to 
filter the query results from SDE.  This was what I was getting at with the 
earlier message...

>   // set spatial constraint search shape
>   envelope.minx = MS_MAX(rect.minx, envelope.minx); // crop against SDE 
> layer extent *argh*
>   envelope.miny = MS_MAX(rect.miny, envelope.miny);
>   envelope.maxx = MS_MIN(rect.maxx, envelope.maxx);
>   envelope.maxy = MS_MIN(rect.maxy, envelope.maxy);
>
>   status = SE_shape_generate_rectangle(&envelope, shape);
>   if(status != SE_SUCCESS) {
>     sde_error(status, "msSDELayerWhichShapes()", 
> "SE_shape_generate_rectangle()");
>     return(MS_FAILURE);
>   }
>   constraint.filter.shape = shape;

Howard