GIS Data Catalog

Add Bathemetry data for Puget Sound, Lake Washington, Lake Sammamish.

Indentify which idxp7500 tiles that have bathymetry data to be processed.

Some upland project area tiles processed on the Windows OS with an unix awk emulation command failed to properly enumerate a unique id for each record for the ascii files containing the raw elevation data in the 7500 tiles.

In other instances ascii files still contained a constant value of '1' in the ascii record, a holdover from the Arc Info Tin generation process that was not properly enumerated to a unique sequential id.

Finally a review of the Ascii files indicated that some tiles still contained a final record containing the value 'end', again a requirement of the TIN generation process that was not removed.

All dgm ascii files tiled in the 7500 blocks were reprocessed using an updated awk command that was tested to successfully generate a unique serial integer for all records up to the largest ascii file size.

A windows version of grep was used with the -v flag to remove all occurrences of 'end' or 'End' from any files where this occurred.

The original warehouse files were unzipped, processed as indicated above and replaced.

A final inspection routine unpacked a copy of the files.

A windows version of the unix tail command was used to create a text file of the last 10 records of each file.

These were inspected to ensure sequential numbering was present to the end of the file and that the file terminated successfully.

Review of version 1 township-range tiles indicated substantial edge effects at the boundary where one 7500 tin overlapped an adjacent 7500 tin.

Though systemic this did not occur along all boundaries.

The 100 foot overlap built into the tin extent was designed to reduce edge effects when lattices derived from the tins were merged.

However there continued to be an effect at the edge of the 100 ft lattices possibly due to how the lattice was calculated at the edge.

Adjustments were made to the processing routines to clip the lattice generated from the tin to 12 feet outside the tile bounds.

This still provided an overlap buffer with adjacent tiles yet substantially improved the quality of the merge.

King County DGM Process Step 6: The composite lattice created by merging the individual 7700 tiles extends beyond the extent of the township-range tile.

The composite lattice is clipped to the bounds of the township-range tile using the GRID GRIDCLIP function.

The resulting clipped lattice is defined with projection information using the PROJECTDEFINE command.

King County DGM Process Step 5: A NULL editmask delineating the open water of the Puget Sound and all areas beyond the project area buffer elsewhere was applied to mask out all remaining 'out-of-bounds' elevation values.

This is done mainly to help 'clean-up' the water areas but also cleaned up along the edge of the project area.

The boundary used along the shoreline was designed to be conservative to avoid clipping any valid nearshore elevation values.

The underlying TINs and ASCII point files can be used to recover, if necessary, any points removed by this edit.

King County DGM Process Step 7: The composite lattice is input to the ArcInfo HILLSHADE command with AZIMUTH = 315, ALTITUDE = 45 and ALL arguments.

The output grid is converted to a TIFF image with world file with the GRIDIMAGE command with NONE for colormap and NO on compression to create a default grey-scale hillshade for general use.

The composite ArcInfo lattice and Hillshade TIF are inspected for completeness and general overall quality and copied to Data Warehouse.

King County DGM Process Step 4: Any negative values in the resulting composite lattice are set to NULL.

This is done to eliminate potential erroneous values and potentially confusing statistics.

This tends to eliminate negative values associated with water features, as well as other spurious values.

A 3x3 focalmean filter is executed against all NULL values to infill any inliers that have now been converted to NULL with an elevation approximation based on adjacent values.

The 100 foot overlap of the input lattices reduces the possiblity of creating strong null value edges between tiles so this 3x3 filter is considered as filling only localized NULL 'holes' in the data.

The original unaltered values of any given data point can be found in the underlying TIN or ASCII point file if access to the unmassaged data is necessary.

Vendor DGM Production Step 3: All elevation data was processed on a point by point basis for ellipsoid to orthometric height conversion using the National Geodetic Survey (NGS) Geoid Model, GEOID99.

Datum and coordinate system conversion from WGS84 to the Washington State Plane coordinate system was performed using U.S.

Army Corps of Engineers CorpsCon software algorithms.

Vendor DGM Production Step 1: LiDAR data processing was used to produce the x,y,z elevation points using vendor proprietary lidar data processing software.

Within this integrated process an atmospheric correction was made, which is especially important in regions of relatively low elevation.

Vendor DGM Production Step 2: Data by flight line was combined in a merge process that eliminates redundant points.

Data was also clipped into more manageable one km x one km bounds.

Noise or anomalous returns were filtered from all data during this processing step.

The data was quality checked using commercial software, Spectra Precision TerraModel and TerraVista.

In order to produce a ground surface DEM, vegetation removal was performed on the last return elevation points data by identifying the laser returns from above ground vegetation.

This proprietary algorithm is capable of removing between 90-95% of the trees and most other prominent above ground vegetation from the data.

The data was triangulated into contours and any remaining vegetation or manmade structures and buildings were identified visually and interactively removed from the data.

The data was triangulated again, contoured and visualized to see the effect of the additional elevation point removal and for any final edits that might be necessary.