[GRASS-user] Measuring Stream Lengths
rshepard at appl-ecosys.com
Sat Jan 30 20:24:17 EST 2010
On Sat, 30 Jan 2010, Dylan Beaudette wrote:
> Where did these data come from?
USGS, BLM, USFS.
I have the Hydrography Data Dictionary so I need to closely read it and
find which ancillary tables have the relevant data. It turns out that
there's a lot of it. For the water courses (linear, flowing aquatic
systems), we're told, "This feature has been modeled to allow for flow
modeling. All arcs must point downstream. This layer will be routed using
the LLID identifier for the stream. All associated attributes are stored as
event tables on the LLID routes. The stream routes are indexed starting from
0 at the mouth of the stream to some maximum value at the headwaters. All
route measures will be initially calibrated in kilometers to three decimal
places. As these routes are edited, every effort will be made to keep the
measure value at a given map location from shifting. This will be
accomplished by stretching or shrinking the measure values to accommodate
lengthening or shrinking along the route as its X,Y coordinates are edited."
There is also an E-R diagram that graphically shows the relations among
tables and columns associated with the map table.
So, I need to look for the tables with segment lengths and write a SELECT
statement to get all relevant rows and sum the lengths.
More when I have questions,
More information about the grass-user