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SPECIFICATIONS FOR DIGITAL PHOTOGRAMMETRIC SERVICES 

This document is a reference guide for those providing photogrammetric mapping services for Central 

Federal Lands Highway Division (CFLHD) of the Federal Highway Administration (FHWA), 

Lakewood, Colorado. 

A. GENERAL DESCRIPTION 

The work consists of digital mapping and terrain modeling in CFLHD U.S. Customary Units 

format; also known as the U.S. Survey Foot (one meter equals 3937/1200 feet.). The mapping will 

follow the existing road or a pre determined area. Microstation files containing contours, utilities 

and planimetrics, as well as a 3-D digital terrain model in Microstation V8 format are to be 

provided to CFLHD. The technical requirements section of this specification document indicates 

more specific requirements. 

B. EQUIPMENT REQUIREMENTS 

Photogrammetric digitizing will be done with softcopy. The final files will be in Microstation V8 

format. Contours are to be generated using Geopak Road Design software. 

C. TECHNICAL REQUIREMENTS 

1. GRAPHICS FILES 

All 3-D design files will be created from the seed file furnished by CFLHD: Sur_ft3D.dgn. This 

seed file is being provided to establish proper parameters (e.g., working units, global origin, etc.) 

to assure CFLHD compatibility. The accepted level, color, text style, line style, line weight and 

cell and symbology structure is found in the MS Word document named “CFLHD-map-symbolcell-table-V8-k.doc”. Current CFLHD file naming convention guidelines will be followed. The 

Verdana font is to be used to label descriptive text. All text should be upper case. 

a. A 3-D compilation index file will be created with the “ndx” extension and symbolized with 

the photo outlines on named level E_MAP_Mapping_Flight_Line, color 0, line code 2 and 

weight 1; the outline of the actual mapping area will be on named level 

E_MAP_Misc_Described_Line, color 4, line code 3 and weight 1. Place flight line labels on 

E_MAP_Mapping_Flight_Line using text size 20 and color magenta. 

b. Create a 3-D digital terrain model (dtm extension) file containing line strings, ground shots 

and closed line strings. These symbolized features shall depict the topography in the true X, 

Y, Z position. The line strings are further broken into two types; each with a specific function 

and specified parameters, the most critical being the correct level. 

1) Discontinuity lines (break lines) are line strings (NOT COMPLEX LINES OR ARCS) 

with the characteristics: line code 0; weight 1; color 0 and placed on the named level 

E_GEO_Break_Line. These line strings establish the X, Y, Z coordinates of the existing 

ground as digitized. 
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a) Discontinuity line strings will be digitized longitudinally along all natural and man 

made “break lines” or discontinuities. A shot is to be recorded at each break along the 

discontinuity and at intervals so that the distance between recorded shots does not 

exceed 25 feet. 

b) Establishing accurate discontinuities is very critical for highway design. The features 

of importance include, but are not limited to: 1) edge of pavement, 2) roadway ditch, 

3) top of roadway cut, 4) toe of roadway fill, 5) drainage lines, 6) ridges, 8) edge of 

water and 8) retaining walls, etc.. 

2) Obscurity lines are line strings used to denote the boundaries of obscured areas with the 

characteristics: line code 3; weight 0; color 3 (red); named level E_MAP_Obscured_Area 

. 

a) If the digitizer cannot see the ground over a large area due to shadows, vegetation, 

buildings or no stereo coverage, the obscured area should be outlined with a closed 

line string. Any data inside an obscurity boundary is disregarded by CFLHD software. 

 Therefore, ground shots and discontinuity lines should not extend into an obscured 

area. It is anticipated that, except for buildings, the number of obscurities shall be 

minimal. CFLHD should be contacted before proceeding if many areas are obscured. 

b) The line strings which comprise obscured areas must form a closed shape. The data 

points used to form the shape are part of contour interpolation and therefore must 

represent the X, Y and Z coordinate of the ground at each respective point. 

3) Ground shots shall be shown with center justification, using the cell named “ground shot” 

symbolize using weight 5, color 3, line code 0 and on named level E_MAP_Ground_Shot. 

 

a) The portion of the model which is within the designated mapping limits is to be 

digitized by placing a cell at the appropriate X,Y and Z coordinates. The ground shots 

may be placed in a grid pattern, not to exceed 40 feet transversely or longitudinally to 

the direction of the flight line. Additional shots should be taken where spot elevations 

need to be shown on the final map. These areas include all tops, saddles and 

depressions. Other locations pertinent to highway engineering, such as road 

intersections, road crests and sags, the centerline of a road at culvert crossings and the 

flow line of visible culvert inlets and outlets are to be depicted with a spot elevation in 

the map file. 

b) Ground shots will not be digitized within 1 foot of a discontinuity or break line. A 

vertical discrepancy between a ground shot and a discontinuity point, which are 

digitized at approximately the same X, Y coordinate, may result in contouring 

problems. Therefore, it is recommended that discontinuities be digitized prior to the 

ground shots. 

c) Although the ground shots will generally be spaced at regular intervals, it is not 

mandatory. If it is advantageous to deviate from the normal grid pattern to depict a 
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unique feature or in order to avoid heavy vegetation, shadows, etc., this is allowed to 

the extent that the deviation does not exceed 1 foot in any direction. 

c. Create a 3-D graphics file containing line string contours extracted from the 3-D dtm file. 

This file’s extension shall be “con”. The contour interval shall be one foot with five foot 

index lines. The index contours shall be labeled with the appropriate elevation with spacing 

of not more than 200 feet. Index contours less than 200 feet in length, shall have a minimum 

of two labels. Labels are to be placed so that they read uphill. The contours will be edited and 

regenerated if bad shots are evident. Modifications to the contours need to be made to 1) 

show depressions (using the depression line style), 2) delete contours where buildings coexist 

and 3) show contours that may not meet the accuracy requirements due to obscurities (using 

closed line strings). 

e. Create a 2-D “map” file containing all man made land use features, structures, and utilities 

that are visible on the aerial photography or annotated on control photos. All features will be 

digitized or symbolized in their true ground coordinate position. Features pertinent to 

highway engineering (such as road turnouts, parking areas, wide shoulders, rock slide areas, 

etc.) are to be digitized and labeled in the file accordingly. CFLHD cells are located in the 

cell library smrowV8-k2006.cel and line styles are available in the resource file 

CFL_LineStyles.rsc. Use the symbology, color, text style, line style, line weight and cell 

symbol listed in the MS Word file “CFLHD-map-symbol-cell-table-V8-k.doc” to depict 

features. Spot elevations should be labeled to the nearest 0.1 foot. 

1) The principal point (photo center) of each photograph used in the mapping will be shown 

in its correct position oriented perpendicular to the line of flight. Digitizing will not be 

done from areas of the stereo model outside the neat model lines, unless requested by 

CFLHD. A line for line join will be made between adjoining flight lines. 

2) Traverse points, (targeted 3000 series) will be shown using the t-point cell symbol. 

Analytical points and wing points should not be shown in the map file. All traverse points 

are to be labeled with the appropriate name with elevations NOT shown. Traverse points 

are in the traverse printout provided to the Contractor. Place t-point symbology using 

precision input or by “snapping” to the exact location. Monument elevations shown in the 

printout may be different from the ground elevations used for the stereo setups. 

2. ACCURACY 

a. Spot elevations, ground shots: Ninety percent of the shots recorded will have a vertical accuracy of 

0.2 foot and a horizontal accuracy of 0.4 foot. 

b. Break Lines: Ninety percent of the shots recorded will have a vertical accuracy of 1 foot and a 

horizontal accuracy of 0.2 foot. 

c. Planimetrics: Well-defined features will be within 0.2 foot horizontally of their actual location. 

1) As indicated above, the accuracy requirements are more stringent than those required for 

typical contour mapping. The 3-D digital terrain files are to be used by CFLHD for 

triangulation and cross section extraction and thus require cross section accuracy. 

L:\SURVEY\QAQC\CFLHD Current Standards and Specifications for SMROW\CFLHD-English-SoftcopyMapping-Specifications-k.doc