NHD Flow Check

NHDFlowcheck is a utility for geometric network creation and validation of an NHD Flowline feature class that exists in a NHD dataset in the form of a personal geodatabase. It features tools that perform the following functions: generation of a geometric network on the NHDFlowline feature class, check for duplicate features, check arc frequency at junctions (nodes), identify flowline features that are not traversed in at least one sub-network with a pour point, flip one or more selected flowline features, and set the FlowDir field of one or more selected flowline features. It is recommended that this entire guide is read to efficiently use NHDFlowcheck. Comments about NHDFlowcheck can be sent to lstan@usgs.gov.

The geometric network is used for several checks performed with these tools, and a new geometric network on the NHDFlowline feature class may be generated. However, it has been noticed that existence of a topology class within the Hydrography dataset can cause the geometric network generation process to fail. Therefore, all topology layers should be deleted from the Hydrography dataset prior to generating a geometric network. Topology layers can be deleted through ArcCatalog.

1. Introduction

The Geometric Network Editing extension, which is a standard ArcMap extension, may be required to identify if the geometric network includes any invalid geometry features or inconsistent connectivity. The following four types of geometries are invalid for features in a geometric network: (1) empty geometry, (2) geometry with multiple parts, (3) begin and end vertices are the same, and (4) geometry has zero length. A geometric network must be built before the Geometric Network Editing extension may be used. The ‘verify network feature geometry’ command in this extension identifies and selects features having invalid network geometries. The type of error may be determined with the ‘network build errors’ tool in this extension. Use of this tool is required when Null values are found in the OrigAZ or OrigFD fields for all records of the NHDFlowline feature class (see command d: Check OrigAZ and OrigFD for Null Values).

2. Installation

If an earlier version of the NHDFlowcheck has been installed then it should be uninstalled by double clicking on the flowcheck_unregister.bat file, which should reside in the NGTOC\NHDGCT\ subdirectory of the drive where the software was originally written.

Installation of NHDFlowcheck is completed by unzipping the latest version of the flowcheck zip file and extracting the files directly to a root drive (e.g. D:) using the folder names included in the zip file. After extracting the files, flowcheck_install.bat and flowcheck_unregister.bat files should reside under the subdirectory NGTOC\NHDGCT\ of the root drive where the files were extracted (e.g. D:\NGTOC\NHDGCT\). Double click on the flowcheck_install.bat file to install and register the NHDFlowcheck dynamic-link library (dll). The flowcheck_unregister.bat file can be used to uninstall the software whenever a new version becomes available. Unzipping the files directly onto the root drive, as described, ensures easy access to the associated documentation.

When using flowcheck to generate a geometric network, you may receive an error message that resembles the following:

Automation Error: Increase MaxLocksPerFile registry.To overcome this problem, Solution: double click on the

AdvancedArcMapSettings.exe in the Program Files/ArcGIS/Utilities folder, which will display a form menu similar to the one at the right. Select the editor tab and increase the jet engine max # of records to calculate to 2,000,000, and click ‘Apply’ button.

3. Processing ConditionsSome of the checks performed by these tools implement Arc Info

workstation commands which require an Info workspace. Therefore, the NHD personal geodatabase to be reviewed should be located in a folder that does not include any spaces or ‘#’ symbols in the path name. Existence of a space or # symbol in the path to the data will cause a processing error when an Arc Workstation command is issued by the tools. In addition, geodatabase names that are opened or edited with this application should not have a name that exceeds 28 characters.

The geometric network is used by several checks performed with these tools. A new geometric network on the NHDFlowline feature class may be generated at any time. However, it has been noticed that the existence of a topology class within the Hydrography dataset can cause the geometric network generation process to fail. Therefore, all topology layers should be deleted from the Hydrography dataset prior to generating a geometric network. Topology layers can be deleted through ArcCatalog.

ArcMap:NHDNHD Flow Check>Using Database: <unset>

Choose DB…

Navigate to personal geodatabaseOpen

Use DB

NHD Flow Check will load: NHDFlowline, NHDArea and NHDWaterbody

NHDNHD Flow Check>Generate Geometric Network

Geometric Network Successfully compacted

Geometric network generation completed

NHDNHD Flow Check>Check OrigAZ and OrigFD for Null Values

If you added some new features to the network and they have negative comids then they will not be added to the status table with the 'write status records' command. So, you can calculate the origAZ value to 0 and calculate the origFD = Flowdir. You should be able to do selecting the records in the NHDFlowline attribute table and then calculating the fields (If a geom. network exists, then you'll need to start and edit session). Once you've populated all origAZ and origFD values, the 'write status records' command should generate the status records for any features that were flipped after the initial geometric netword was generated (These should have positive comids) (It will also write status records for features with modified the flowdir values.

NHDNHD Flow Check>Locate Duplicate Nodes

No duplicate nodes found in dataset

NHDNHD Flow Check>Locate Duplicate Arcs

Two duplicate features selectedLoading into error queue

NHDNHD Flow Check>Zoom to feature

In this case the mid-point of the two features are within 10 meters and thereforeare flagged as an error. This is a false positive

NHDNHD Flow Check>Next

You can doc “Next” on the tool bar.See next slide.

Doc “Next” on the tool bar

Click ToolsClick CustomizeSelect CommandsHold down left mouse button on “Next” and drag to tool bar

Second feature identified as error (false positive)

NHDNHD Flow Check>Generate Connection Tables

Connection table generation successful

NHDNHD Flow Check>Check for Degree Problems

Thirty five potential errors have been selected

NHDNHD Flow Check>Zoom to Feature

NHDFlowlineSet symbology to arrow at end

False positive

NHDNHD Flow Check>Next

False Positive

Missing linework?

Opposing flowFlip selected arc

NHDNHD Flow Check>Flip Arc

Arc has been flipped

Review all records in queue then move on toFind Network Ends

NHDNHD Flow Check>Find Network Ends

One hundred sixty seven ends selectedOK

OK

Export selected network ends to feature class for visual inspectionNHDFlowlineDataExport Data…

Export: Selected featuresThis layers data sourceBrowse to personal geodatabase

Select personal geodatabaseHydrographyName: network_endsSave

OK

Yes

Network ends feature class:Set symbology

Systematically check dataset to insure that network ends are validIn this case the network end is valid

Systematically check dataset to insure that network ends are validIn this case the network end is invalid

Notice that the StreamRiver below the dam is uninitialized and therefore the artificial path is treated as a network end

NHDNHD Flow Check>Set Direction: With Digitized

Review all records in queue then move on toFlow Check

NHDNHD Flow Check>Flow Check

Typically the selected set is correct however you dohave the option to choose ‘No’ and add additional flowlines to selected set

Three hundred forty eight features were not traversed(Uninitialized features)OK

Export selected features not traversed to feature class for visual inspectionNHDFlowlineDataExport Data…

Export: Selected featuresThis layers data sourceBrowse to personal geodatabase

Select personal geodatabaseHydrographyName: ‘not traversed’Save

OK

Yes

not traversed feature class:Set symbology

Systematically check dataset to insure that features not traversed are validIn this case the features are uninitialized and can be set to withdigitized

NHDNHD Flow CheckWrite Status Records

OK

This will avoid multiple metadata status recordsOK

OK

Status entries have been populated in NHDStatus table

Delete Geometric NetworkThis will delete the geometric network and other tables created in NHD_Flow_Check (conArc, conNode, NHDErrors, and NHDErrorState).All these files must be deleted before you reproject to geographic.