In 1991, a group of three individuals (a full-time researcher and two graduate students) started conducting research on conversion of 7.5’ quadrangles into DLG-3 files. The first responsibility of this group was to evaluate existing commercial software. After six months of research, it was evident that no commercial software could perform the conversion process in a cost-efficient fashion. Since then, the research and development group’s emphasis has shifted toward implementing its own solutions, using existing software as much as possible. The group has grown; currently there are five graduate students working under the supervision of the project manager (principal investigator). The major accomplishments of this group are described next.

RETSAM_PC_CFM

The heart of digitizing, attribute tagging, and error correction is the RETSAM_PC_CFM software. This program is based on the RETSAM program developed at the USGS in the workstation (UNIX) environment. The version developed at the CFM is PC-based (MS-DOS) and has replaced a digitizing table as an input device (heads-down digitizing) with a mouse (heads-up digitizing). Paper menus have been replaced by on-screen icon menus, and RETSAM_PC_CFM can display raster images as backdrops.

The different options existing in the paper menus (hydrography, hypsography, roads, etc.) have been integrated into the on-screen icons, making it very easy to shift from a particular layer to another. Many new functions have been added and some old RETSAM functions have been eliminated. One purpose of the new functions is to provide an easy and efficient way to display and manipulate the raster image for data collection and correction.

Two new options not available in RETSAM are the TAGGER and the CONTOUR_EDITOR options. The TAGGER attaches attributes and elevations to contour lines in an interactive but very efficient fashion. This program has decreased the time expended in this operation by more than 70 percent. The CONTOUR_EDITOR is based on Intergraph’s PROBLEM_EDITOR option of the I/VEC program (UNIX only). CONTOUR_EDITOR makes use of the problem file (.PBM) generated by I/VEC during the raster-to-vector conversion process. This file is used in the PC environment by the CONTOUR_EDITOR to show possible errors in the conversion process and allow their correction by providing a set of editing tools. This program decreases correction time for hypsography by automatically driving the independent contractor to the problematic areas.

RETSAM_PC_CFM is a mix of ‘C’ programs, Intergraph’s MDL programs, User Commands, and Side Bar menus built on top of Intergraph’s Microstation.

CFM_WARPING_SYSTEM

Warping of raster images is one of the first steps in the conversion of quadrangles. Earlier in the project, Intergraph’s program was used for this operation, but two different circumstances made this approach inefficient. First, the program is hardware-dependent (it runs only in Intergraph workstations) and, second, only one of the different transformation options (the six parameters affine) of the program is reliable. Warping is done by the CFM staff; therefore, warping should be done in the most cost-efficient fashion. Warping images in the Intergraph workstation is an interactive process. Obtaining acceptable residuals in this process requires a great deal of operator interaction. In addition, warping large images (over 20 megabytes) in the type of Intergraph workstations (Model 6000) available at the CFM is very time-consuming.

The CFM developed a highly automated warping program able to run in different hardware platforms (including our mainframe). The result is the CFM_WARPING_SYSTEM. This is a set of ‘C’ programs that automatically locates the tic marks in the corners of the raster images using autocorrelation methods. This system then extracts the corresponding geodetic coordinates from a GISOM master file, transforms them to the UTM system, computes a six- parameter affine transformation from the raster image space into Intergraph’s design file space, and evaluates the residuals. If they are acceptable, it computes a projective transformation (eight parameters) and uses a backward resampling approach to move the raster image to the new space. Results are stored in a new raster file. The entire process is controlled from UNIX script shells.

GAP_CHECKER, LINE_CHECKER

These programs have been developed to decrease the amount of manual editing necessary in the hypsographic vector files generated by I/VEC. GAP_CHECKER locates small gaps in the vector lines. This program analyzes the topology and elevation information of a .DD file to locate any gaps along contour lines. DD files are topological structure files used as intermediate files by the USGS. They are generated from PROSYS’s DCF files. Area information in the .DD files is analyzed; whenever an area with the same ID is found at both sides of a contour line, a gap is detected. The locations of the gaps are recorded and are used to generate a reference design file with square shapes marking the beginning and end of the gaps. This file is displayed with the one generated by I/VEC, and it is used by the independent contractor to close erroneous gaps.

The purpose of LINE_CHECKER is to correct some errors in the line segments generated by I/VEC. Usually, these errors occur at the end of line segments and are very difficult to find by simple visual inspections.

CFM_PLOT

This program plots raster and vector files from a PC. Files to be plotted are copied automatically to the plotting directory, and the operator sets the plotting parameters (paper size, scale, etc.) and then issues the plotting command. Files are plotted automatically.

Current Development

Four major projects are in different stages of development: highly automated contour conversion, computer-based line work evaluation, highly automated hydrographic conversion, and highly automated transportation conversion. The object of the highly automated contour conversion project is to implement a cost-efficient solution for converting raster contours into vector form. At this point, the program is operational and the beta test phase is almost completed. This program is able to convert normal contours, carrying contours, and feather contours. This program generates the vector representation of the contours with the proper DLG-3 attributes (including the elevation) in a highly automated fashion.

The computer-based line work evaluation program seeks to replace the costly and inefficient visual evaluation of line work with a computer approach. For layers such as hypsography, hydrography, PLSS, and boundaries, a fully automated solution may be possible. For the transportation layer, an interactive solution seems to be possible. At this point, a program is operational for hypsography and it is undergoing beta test.

The object of highly automated hydrographic conversion is to develop a solution for converting raster hydrographic data to vector form with minimal human intervention. This project is in a very early stage. At this point, a prototype interactive line following program is operational. Additional research is being conducted to increase the amount of automation.

The highly automated transportation conversion project will develop a solution for converting raster transportation data into vector form. This is considered a very difficult program, and we are still developing the conceptual framework.

Back to the Center For Mapping Homepage

Back to GISOM HomePage

---

Please send Comments and Sugestions to Kosta Bidoshi

---