FLOOD06523 - Laserfiche WebLink

Home Browse Search

letters shall be not less than 0.1" in height and shall be clearly legible. All overlay lines and lettering shall be black or as specified by the contracting agency or its representative. 2. Conventional Rectification Methods. By this method, the contractor shall produce a photographic background with contours by correcting for the effects of tilt and relief prior to pasting down the photos on a base network of horizontal control. These photo- maps have been found to be fairly accurate in flat terrain. The contractor shall obtain the best contour match near the stream reaches. For the purpose ofthis specification, it shall be considered that conventional rectified photo-maps with contours will not meet "National Map Accuracy Standards." Therefore, to meet the accuracy requirements of the contract, the contractor shall provide a line map showing contours and topographic features at no extra cost. No photo-maps shall be acceptable with rectified enlargements greater than five diameters from the flight photography. 3. Ortholtonal Proiection (Orthophoto) Method, In this process, differential (incremental) elements of photographs are photogrammetrically repositioned with the aid of an orthophoto scope (ortho-scanning). This is a linear incremental transformation that results in the scale of the stereo model being uniform throughout for the mapping area. Each stereo model shall be scanned with a slit width and at a speed which will achieve uniform town and aesthetic and accurate mapping. During scanning, the floating mark shall generally be kept in contact with the ground, even to the extent of passing the mark through walls, buildings, trees, and other features having discernible height. a. All raw orthophoto negatives shall have fine-grained quality, normal uniform density, and such tone and degree of contrast that photographic detail of the original aerial negatives is preserved to the maximum extent possible. Raw orthophoto negatives shall also be free of objectionable scan lines, image discontinuities, double exposures, and out-of-focus images. Exact final scale negatives, are desirable, which can be obtained by direct sheetsized scanning from the neat model or by mosaic splicing of the negatives, Ifthe negatives are formatted by mosaicking, the splicing shall be minimized, Variance in tone and/or color contract between mosaicked segments of an individual formatted orthophoto and between adjacent map sheets shall not be objectionable to the eye.