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RhysHJ

Velocity vectors

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Hi,

We are using TUFLOW_to_GIS.exe to export mid/mif velocity vectors, then importing into ArcGIS to produce maps. The approach is mostly successful, but on a couple of occasions we've had display problems that seem partially to do with the vectors being defined as polygons rather than "true" vectors with a magnitude and orientation. ArcGIS has the capability to create vector arrows based on point features with magnitude and direction attributes rather than defining the arrow itself as a polygon in space.

Are there any alternatives to this polygon vector output from TUFLOW_to_GIS, or any chance of getting such a feature on the wish list? Otherwise, has anyone had a similar problem and found the cause of the display issues we're having within ArcGIS itself?

Thanks in advance

Rhys

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Yes, this is a known problem with ArcGIS in that it doesn't like polygons that have perimeters that trace back over themselves as occurs with the tail of the arrow. To overcome this, an option was incorporated into the predecessor of TUFLOW_to_GIS (called sms_to_mif) that produced arrows with a thick tail. This option wasn't kept when the sms_to_mif code was transferred to TUFLOW_to_GIS, but will add it to the list to re-include! We could also look at the option of outputting as symbols (point objects) with different angles and sizes (similar to the _TS.mif output), although the polygons have always been favoured because they are considered to look better.

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I have an ArcGIS script which will take an x-velocity grid and y-velocity grid and convert these into a shape file. The new shape file contains points at each cell centre with vector magnitude and direction attributes calculated. This shape file can then be labelled using a proportional directional symbol (arrow) in ArcGIS. Depending on the size/resolution of the study area I've found the arrows can draw up or refresh quite slowly compared with Mapinfo.

I don't know whether TUFLOW can produce x and y grids of max velocities. At any rate, I'm happy to share the ArcGIS script or methodology behind the code.

Regards,

Paul Ollett.

Gold Coast City Council

pollett@goldcoast.qld.gov.au

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We actually have a similar script Paul (for processing other software outputs), but I'm not aware of a way to get u and v grids out of TUFLOW. I agree the refresh rate can be frustrating.

Bill, is there a possibility of adding a "direction" attribute to the existing .mif output (the point feature version) as well as the value? That would make life easy enough for those who use ArcGIS for their velocity figures.

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