QUESNEL PEM DEM Digital Elevation Model Preparation. Summary Report

Transcription

1 QUESNEL PEM DEM Digital Elevation Model Preparation Summary Report Quesnel Contract # FIA Williams Lake Contract # FIA Mile House Contract # FIA Jan 20, 2006 Meridian Mapping Ltd Bay St. Nanaimo, B.C. V9T-3A4

2 Table of Contents Introduction:... 1 Scope:... 1 Figure Figure Figure Table Table Methods:... 4 Notes:... 5 Data Delivery:... 6 Appendix Specifications... 7 Arguments... 7 Input Data... 8 Deliverables... 9 Appendix Trim 1 Source...10 Appendix Evaluation of data issues and problems...11 Meridian Mapping Ltd i

3 Introduction: In in support of the Predictive Ecosystem Mapping process, Meridian was tasked with creating a seamless digital elevation model encompassing the entire Cariboo Forest Region. Meridian had previously completed two processing runs during 2003 and 2004, resulting in a seamless DEM coverage of the study area depicted in Fig. 1. The 2003 processing area as depicted in Figure 1, was delivered as a separate dataset in The deliverable for the 2004 processing encompassed both years processing. The DEM study area encompassed all remaining sheets within the Cariboo Forest Region as outlined in Fig2, and the deliverables specified a merge of all Chilcotin data. This report will outline the processing methodologies and issues as they pertain to all years processing, as the processing format was identical for all years and the issues were similar. Scope: In 2003, a large central block was completed followed by areas to the west and east in 2004, as depicted by yellow outline in Figure 1. These areas totalled 305 Trim sheets as detailed in Table 1. For 2005 a total of 357 Trim sheets were processed to complete coverage of the Cariboo Forest Region. The three study areas were processed in strips and merged at the completion of the gridding process. See table 2 for a complete list of trim mapsheets processed in Figure study areas 2004 Processing 2003 Processing 2004 Processing Meridian Mapping Ltd 1

4 Figure study areas Figure merged study areas Meridian Mapping Ltd 2

5 Table 1. Trim sheets used in DEM Preparation Sheets 2003 Sheets East 093H B F A H B F A H B F A H B F A H B F A West 093B G A C B G A C C G A C C G A C C G A F C (180 sheets total) 093B (125 sheets total east 093C B and west) 093C B C Meridian Mapping Ltd 3

6 Table 2. Trim sheets used in DEM Preparation Mile 093A P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P O P P P P P P P P P O P P P P P P P P P O P P P P P P P P P O P P P P P P P P P O P P P P P P P P O P P P P P P P P O I I I I I I.091 Williams Lake 093C C C C C C C C C C C C C C C C C C C C C C C B B B B C C C C C C C C C B B B B C C C C C C C C C B B B B N N N N N Processing Sheets 092N N N N O O O O O O O O O O N N N N N N N N N O O O O O O O O O O N N N N N N N N O O O O O O O O O O N N N N N N N O O O O O O O O O N N N N N N N O O O O O O O O O N N N N N N N O O O O O O O O O N N N N N N N O O O O O O O O O N N N N N N O O O O O O O O O N N N N N O O O O O O O O O N N O O O O O O O O K J J J J J J J J.083 Quesnel 093H H H H H H H H H H H H H H H H H H H H H H H H H A A A A A A A A A A.090 Methods: The processing methodology for all years follows the steps laid out in the Schedule A attached to each years contract (See appendix 1 for details). All steps comply with the Appendix 1 methodology unless otherwise noted. Any deviation from the Appendix 1 methodology were cleared with the contract monitors Nona Phillips, Dave Moon and/or Bob MacMillan. Meridian Mapping Ltd 4

7 Notes: The steps are summarized as follows: Compile raw Trim I format data into sinks, lakes, islands, and rivers coverages with the appropriate feature types filtered for processing as per the specifications. Polyganize the lakes data into a seamless coverage. Translate MOEP DEM files to DXF format and then dxf to xyz format. Append xyz files into a ASCII delimited file. Import the XYZ data into a point coverage. The Arc Generate files were not used for this step. Create study area buffers of 200m to assist in the dataset merge process Process the data at 25m grid spacing as per the specifications. Mosaic the individually processed tiles together to form a merged dataset Perform 3x3 followed by 5x5 focal mean filters on the data as per the specifications. Extract a flat lakes subset coverage from the unsmoothed DEM dataset and append smoothed islands into the unsmoothed lakes dataset. Append the flat lakes with smoothed islands back into the smoothed dataset as per the specifications. Mosaic 2005/06 data into the 2003/04 dataset for seamless coverage of Cariboo Region. The resulting dataset is smoothed but includes flat lakes that have been stamped back into the data. As in previous years the decision not to use the generate format ASCII xyz files was taken to ensure all the data found in the Trim I DEM was adequately represented by the xyz file, and had not undergone any preprocessing at the ministry level which may have resulted in data loss or alteration. It was thus decided to process the raw MOEP files to dxf format and then to xyz format. The advantage of this process was the ability to QA trouble spots in the resulting DEM with actual point and linear data. In addition the processing would be identical to previous years, ensuring uniformity across the Region. There are several anomalies in the data which affect the appearance of the completed product. They are as follows: Lake elevation offset: Horsefly Lake spans several mapsheets that do not contain consistent elevation coding in the raw DEM data. As a result of this offset the eastern half of the lake is at a lower elevation than the western half resulting in a step in the middle of the lake. Lake polygon size issues: Quesnel Lake spans approximately 18 TRIM sheets. The size of the vector polygon presents technical issues during the gridding process. To facilitate processing, the polygon was split into several pieces. These split boundaries that bisect the lake can be seen as raised linear features within the lake polygon. These issues have been discussed with Bob MacMillan and Dave Moon, and it has been determined that since areas within lake polygons are removed from Bob MacMillan s process, artifacts within lakes are not a concern. No further action has been taken in regards to these issues. Other issues which relate to all years processing are as follows: Cliff effect along lakeshores: The edges of many lakes appear to have a vertical wall from the lakeshore to the surrounding terrain. This is an unavoidable effect of stamping the flat lakes back into the smoothed DEM. Meridian Mapping Ltd 5

8 Surface pitting: Some areas appearing as pits will be very small lakes that have been stamped back into the terrain as detailed above. Other areas are legitimate depressions as reflected in the raw TRIM data. Extensive checks of these areas were performed and documented for the 2003 DEM processing work. Seams: The appearance of seams along some mapsheet boundaries and between adjacent flightlines are due to slight elevation offsets between the stereo models used to create the raw TRIM DEM. Please see Appendix 3 for a complete discussion of these issues as pertains to the 2003 processing. There are no other issues evident to us after a thorough check of the completed DEM. The 2005/2006 processing did not uncover any other issues not already addressed in previous years processing. Data Delivery: Data delivered via CD-Rom includes the following input coverages and final gridded data: Lakes: Filtered dataset does not contain wetlands Islands: Contains all islands Rivers: Contains all rivers Sinks: Sinks extracted from the twtr coverage Study Area: Encompasses all completed mapsheets DEM: Seamless smoothed 25m GRID format with datasets. Report: Summary processing report All data is in Nad83 UTM Zone 10N. Meridian Mapping Ltd 6

9 Appendix 1 Deliverable specifications as outlined in contracts for each processing year. Specifications Procedures to be followed as listed below. Exceptions to these procedures will be jointly agreed to by Dr. R.A. MacMillan, Meridian Ltd., and David Moon, CDT Core Decision Technologies Inc. DEM data will be received as individual 1:20,000 mapsheets in ARC GENERATE format. Generate files are ASCII files that are formatted for reading by ARC/Info or Arc View. Each TDEM.GEN file will be merged into one large ASCII text file. This will be converted to a shapefile using Arc View s Import Data Source utility, preserving their elevation values. The resulting shapefile will be converted to an Arc/Info point coverage, and then re-projected into UTM 10 NAD 83. The TWTR layer (hydrographic features) contains point data describing various features. Some of these points are sinks (known topological depressions). These points (FCODE HB ) will selected and converted to an ARC/Info point coverage, preserving their elevation values. The resulting coverage will be re-projected into UTM 10 NAD83. Streams and lakes will also be taken from the TWTR layer. All streams (definite and indefinite) will be used to make the DEM. Lakes (definite and indefinite) will be polygonized and used to flatten water bodies. These coverages will then be reprojected into UTM 10 NAD83. TRIM neatlines will be concatenated into a single coverage, and re-projected to UTM 10 NAD83. The ARC/Info TOPOGRID command will be used to create the DEM. TOPOGRID <out_grid> <cell_size> Arguments <out_grid> - the grid to be created. <cell_size> - the cell size, in map units, of the output grid. A cell size of 25 meters will be used. A wide array of subcommands are available when using this command, but only those to be used are listed. BOUNDARY keyword and parameter for input of a polygon coverage representing the outer boundary of the interpolated grid. The concatenated TRIM neatline coverage will be used as the boundary. DATATYPE the primary type of input data. Valid arguments for this are SPOT or CONTOUR. Since points are being used instead of contours, SPOT will be chosen. ENFORCE turns the drainage enforcement routine on or off. The default is on. This option will be left ON to enforce hydrological consistency. Meridian Mapping Ltd 7

10 LAKE a polygon coverage of lakes. The polygonized lake coverage will be used to insure flat lakes. POINT keyword and parameters for input of a point coverage representing surface elevations. The DEM point coverage will be specified along with the attribute containing elevation values. SINK keyword and parameters for input of a point coverage representing known topographic depressions. The point coverage containing known topological depressions will be specified here, along with the attribute containing elevation values. STREAM keyword and parameters for input of a line coverage representing streams. The streams coverage created from the TWTR layer will be specified here. TOLERANCES a set of tolerances used to adjust the calculations of the interpolation and drainage enforcement process. These tolerances are used to adjust the smoothing of input data and the removing of sinks in the drainage enforcement process. Tolerances are listed below. {tol1} - this tolerance reflects the accuracy and density of the elevation points. Data points which block drainage by no more than this tolerance are removed. This should be set to half of the contour interval when using contour data. The default is 2.5. If input data are sparse, this parameter may be set to a higher value to produce a more generalized output grid. Since there should be an abundance of input data, this is set to 1. {horizontal_std_err} - this parameter represents the amount of error inherent in the process of converting point, line, and polygon elevation data into a regularly spaced grid. It is scaled by the program depending on the local slope at each data point and the grid cell size. The default value is 1.0. Larger values will cause more data smoothing, resulting in a more generalized output grid. Smaller values will cause less data smoothing, resulting in a sharper output grid (which is more likely to contain spurious sinks and peaks). Any non-negative value is permitted. Recommended values are between 0.5 and 2.0. The default value of 1 will be used. {vertical_std_err} - this parameter represents the amount of random (non-systematic} error in the z-values of the input data. In most elevation data sets, it should be set to the default value of 0. If the data contains significant random vertical errors, with uniform variance, set this parameter to the standard deviation of the errors. The default value of 0 will be used. The resulting DEM will then be smoothed twice. The first smoothing operation will be a low pass filter using a focal mean with a 3x3 kernel. The second smoothing operation will be a focal mean with a 5x5 kernel. The resulting DEM will be saved, and lake elevations re-applied to the DEM to ensure that the smoothing did not displace the flat water bodies. A hillshade will be prepared and checked for obvious errors. The hillshade will be forwarded to Dr. R.H. MacMillan in Arc View Grid format for review and approval. Input Data The licensee will provide the contractor with individual 1:20,000 map sheet files in ARC GENERATE format for all data to be processed into the seamless DEM coverage. Meridian Mapping Ltd 8

11 Deliverables The contractor will deliver a seamless digital DEM database and hillshade in Arc View Grid format for the final project area. The final format will be specified by Dr. R.A. MacMillan, LandMapper Environmental Solutions but will be a standard ArcInfo or ArcView supported data format. Meridian Mapping Ltd 9

12 Appendix 2 Trim 1 Source Trim 1 was used for all the processing and included the DEM as well as the vector layers used as inputs in the gridding process. Working projection was UTM Nad 83, Zone 10. Planimetric coverages were translated to UTM for processing. Name: Terrain Resource Information Mgmt Program - Positional (TRIM) Description: Topography, Planimetry, Elevations, and Toponymy (place names) for all of British Columbia. Produced by Geographic Data BC. Purpose: Corporate Base map for the province that all resource information is referenced to. Program: Base Mapping and Geomatic Services Admin Location: Victoria Geographic Availability: British Columbia Time Period: Information is directly compiled from stereo aerial photography dating from Accuracy: See British Columbia Specification and Guidelines for Geomatics - Digital Baseline Mapping at 1:20,000 Known Anomalies: See British Columbia Specification and Guidelines for Geomatics - Digital Baseline Mapping at 1:20,000 Map Datum: North American Datum 1983 Map Projection: Albers Equal Area using BC Government (RIC) parameters Map Scale: 1:20,000 Map Resolution: See British Columbia Specification and Guidelines for Geomatics - Digital Baseline Mapping at 1:20,000 Meridian Mapping Ltd 10

13 Appendix 3 Evaluation of data issues and problems The following is an excerpt from a discussion with Bob MacMillan regarding the 2003 processing. The DEM contained several anomalies common to Trim in the area. These issues pertain to both the 2003 and 2004 processing. Qdem1_Strange_Peaks_Spikes_example1.jpg We have checked the raw TRIM DEM XYZ points and lines as well as the bedrock geology in this area. The cones features that you see in the DEM are part of the Anahim Volcanic Belt which has some very recent volcanic activity (Pleistocene ( Ma). Qdem1_Dam_And_Funny_Lake_example1.jpg This unusual topography is the Gibraltar open pit mine north of McLeese Lake. The lake is actually a tailings pond with the dam on the north end. You will notice the open pits just south of the pond. Qdem1_Map_Edges_Seams_example1.jpg There is a significant visible seam on the north and west sides of 093B035 and to a lesser extent in other map sheets. Unfortunately this is present in raw TRIM DEM data and we have no way of rectifying it. Qdem1_Map_Edges_Seams_Lakes_example2.jpg Most edge effects along lakes were due to the pixel offset noted above and have been fixed. The remaining pixilation or pockmarking is due to steep shores along lake edges and edge effects resulting from the flat lakes being stamped back into the surrounding terrain surface which has had smoothing filters applied. Qdem1_More Mini Volcanos_example1.jpg See: Qdem1_Strange_Peaks_Spikes_example1.jpg above. Meridian Mapping Ltd 11

14 Qdem1_NS_TRIM_ Striping_example1.jpg This vertical striping is seams between photo lines inherent in the raw TRIM DEM data. Please see example below. Meridian Mapping Ltd 12

15 Qdem1_Pits_Seams_example1.jpg Here is a screenshot of the TRIM XYZ points and break-lines in this area. The terrain is pockmarked with depressions. You can see that the circular breaklines (only the vertex positions are shown) are lower in elevation than the surrounding regular XYZ grid points. Meridian Mapping Ltd 13

16 Qdem1_Seams Facets in Lakes example2.jpg Horizontal striping will be addressed. See topic below re: facets within lakes. Qdem1_Stereo Model Non Flat Lakes example2.jpg We have looked at the TRIM source data for the lake in this screenshot and many other lakes in the project area. There are a number of variations in the raw TRIM DEM data that result in the lake surfaces not being completely flat. Some of these include: Minor variation in the elevations assigned to the lakeshore vectors. This variation is usually not more than +/- 1-2m. Presence of XYZ grid points inside the lake polygon. Due to horizontal inaccuracies, an XYZ grid point will occasionally land inside the lake polygon. This point can have an elevation slightly above or below the level of the adjacent lakeshore. Meridian Mapping Ltd 14