gis-l: RE: measuring distances along NHD river (polyline)

Woeber, Nathan (Andy) Nathan.Woeber at dep.state.fl.us
Thu Sep 5 12:01:53 EDT 2013


Yes, just something to be aware of because there is no alert to those fields of "LengthKM" that what is in those cells are radian measurements and there is no "recalculate geometry" button to update the data in the shape fields to recalculate meters in the geometric projection so you might interpret the values as meters when it is a radian measurement.

If you pull from Dataminer then it will be Albers so no conversion is necessary, however if you get the NHD from another source or REST instance it will be in geometric projection and I believe the measurements are all in degrees from those sources.

From: Abbey, Edwin
Sent: Thursday, September 05, 2013 11:55 AM
To: Woeber, Nathan (Andy); Ali, Eesa; gis-l at lists.dep.state.fl.us
Subject: RE: measuring distances along NHD river (polyline)

Just for clarification, if the NHD is used from Dataminer, it will already be in Albers.  However, there are other sources from which to get the NHD which may be in a different coordinate system.

From: gis-l-bounces at lists.dep.state.fl.us<mailto:gis-l-bounces at lists.dep.state.fl.us> [mailto:gis-l-bounces at lists.dep.state.fl.us] On Behalf Of Woeber, Nathan (Andy)
Sent: Thursday, September 05, 2013 11:12 AM
To: Ali, Eesa; gis-l at lists.dep.state.fl.us<mailto:gis-l at lists.dep.state.fl.us>
Subject: gis-l: RE: measuring distances along NHD river (polyline)

Eesa,
The only caveat to the LengthKM may be that the NHD comes in geometric coordinate system with degrees so those measurements in the shape length and LengthKm are in radians not a true length so you will need to create a new field and convert.   Or go to Albers projection and get meters.

[cid:image001.jpg at 01CEAA2F.B5CB7DC0]


For instance I checked NHDFlowline for a small artificial path with length in the table reported in "Shape_Length" as 0.000445, that is a radian of a circle so its not meters.  I measured the length on the map and it reported
This:
[cid:image002.png at 01CEAA2F.B5CB7DC0]

So be careful interpreting the fields as it has that underlying geometric coordinate system of degrees and you will need to convert to meters.  My advice for true lengths is to project NHDFlowline to Albers which has the underlying measurement of meters then use Edwins suggestions for getting your lengths.  After reprojection to albers then recalculating shapelength I got the table to reflect meters vs radian measurements.

47.396285,  a bit different from the measurement tool but more accurate.


Andy





From: gis-l-bounces at lists.dep.state.fl.us<mailto:gis-l-bounces at lists.dep.state.fl.us> [mailto:gis-l-bounces at lists.dep.state.fl.us] On Behalf Of Abbey, Edwin
Sent: Thursday, September 05, 2013 10:02 AM
To: Ali, Eesa; gis-l at lists.dep.state.fl.us<mailto:gis-l at lists.dep.state.fl.us>
Subject: gis-l: RE: measuring distances along NHD river (polyline)

Good morning Eesa,

Look for the attribute "LengthKM" in the NHDFlowline attribute table.   If you have several flowlines selected, display selected records only and right-click on the "LengthKM" heading and click "Statistics". A popup window will display an assortment of statistics including a sum of the lengths of the selected records.

Alternatively, you can also right-click the heading of a the "Resolution" attribute and choose "Summarize", then in the Summarize window, select "sum" under the LengthKM attribute.  Use the Browse folder for specifying the location and output file type for the table that is created (dbf, gdb table, csv, etc).

In order to select several flowlines between two points, I suggest trying to use the Utility Network Analysis toolbar. On the Analysis drop-down, select Options.  From the Options window, click the Results tab. Make sure the setting for "Return results as" is set for "Selection".

Then, using the "Add Edge Flag" tool, drop a blue flag at the beginning and end of the route you are assessing.  Change the Trace Task to "Find Path" and click Solve.  The flowlines between the flags will be selected.


Hope this helps,

Edwin

Edwin A. Abbey
NHD Coordinator - Environmental Manager
Office of Watershed Services
Florida Department of Environmental Protection
2600 Blair Stone Road, MS 3526
Tallahassee, Florida  32399
phone:  850-245-8550
fax:  850-245-8236
Edwin.Abbey at dep.state.fl.us<mailto:Edwin.Abbey at dep.state.fl.us>

www.dep.state.fl.us/water/watersheds/nhd.htm<http://www.dep.state.fl.us/water/watersheds/nhd.htm>
www.protectingourwater.org


From: gis-l-bounces at lists.dep.state.fl.us<mailto:gis-l-bounces at lists.dep.state.fl.us> [mailto:gis-l-bounces at lists.dep.state.fl.us] On Behalf Of Ali, Eesa
Sent: Thursday, September 05, 2013 9:13 AM
To: gis-l at lists.dep.state.fl.us<mailto:gis-l at lists.dep.state.fl.us>
Subject: gis-l: measuring distances along NHD river (polyline)


Other than dragging a line along a river using the measuring tool, what options do I have to measure distance along a polyline (river in the NHD layer)?

Thanks,

e


Eesa Gafoor-Ali
Environmental Specialist II
Surface Water Assessment & Monitoring Program
8800 Baymeadows Way West, Suite 100
Jacksonville, FL 32256
eesa.ali at dep.state.fl.us<mailto:eesa.ali at dep.state.fl.us>
904-256-1628 office
904-813-1298 mobile



Please take a few minutes to share your comments on the service you received from the department by clicking on this link DEP Customer Survey<http://survey.dep.state.fl.us/?refemail=Eesa.Ali@dep.state.fl.us>.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.dep.state.fl.us/pipermail/gis-l/attachments/20130905/ae3acb9c/attachment-0001.htm
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 26204 bytes
Desc: image001.jpg
Url : http://lists.dep.state.fl.us/pipermail/gis-l/attachments/20130905/ae3acb9c/image001-0001.jpg
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.png
Type: image/png
Size: 5302 bytes
Desc: image002.png
Url : http://lists.dep.state.fl.us/pipermail/gis-l/attachments/20130905/ae3acb9c/image002-0001.png


More information about the GIS-L mailing list