Hard Copy to Digital Transfer: 3D Models that Match 2D Maps
Abstract
This research describes technical drawing techniques applied in a project involving digitizing of existing hard copy subsurface mapping for the preparation of three dimensional graphic and mathematical models. The intent of this research was to identify work flows that would support the project, ensure the accuracy of the digital data obtained, and provide a means of capturing, realizing, and extending the value of an existing investment in subsurface mapping. Mapping used in this project was in hard copy format. Control points for use in digitizing were converted from local coordinates to plane coordinates based on a defined map projection. Since mapping done in this work was to meet National Map Accuracy Standards, calculation of acceptable root mean square digitizing error was necessary and is demonstrated. Two methods are discussed to ensure quality control in digitizing. Preparation of base maps showing drilling data provides a means of estimating map accuracy. Map precision, however, is shown by comparing the congruence of contours as digitized and contours as obtained from the digital model. Where congruence is lacking, the digitizing of supplemental contours or direct editing of the grid itself is required to precisely constrain the 3D model. Efficient work in this project was heavily dependent on use of standard techniques of engineering graphics. To expedite digitizing, a common layering scheme was developed for all oil fields mapped. Control points used in digitizing were selected so as to be common to all mapping, even where multiple maps were involved. In addition, the use of a common map format, color scheme, lettering style, and included metadata materially expedited the work. Finally, the conduct of the work in defined stages provided immediate work products from the project. This facilitated identification of needed changes early in the project and supplied accurate data as soon as digitizing on a specific field was complete.
