STATE BUDGET AND CONTROL BOARD
Office of Research and Statistics
South Carolina Geodetic Survey
Standards and Procedures for County Base Mapping
I. PURPOSE AND INTENT
It is the desire of XXXXXX County to obtain digital orthophoto imagery to support their
mapping projects in accordance with the attached specifications. In addition to information requested in the specifications, all proposals should include contractor’s previous experience on similar projects (with references); proof of a license to practice photogrammetric surveying in
South Carolina; equipment and personnel to be utilized; and proof of bondability. This information shall also be provided for any subcontractor to be employed for this project. A statement must be included in the proposal indicating that all work will be performed in the United States of America. The proposal shall also specify any exceptions to or deviations from the attached specifications.
; Project duration will be specified in Section V. The contractor shall include a sample contract
with the proposal. For the purpose of this proposal, the total number of orthophotos shall be
XXX of which YYY will be at a scale of 1": 400' and ZZZ at a scale of 1": 200'. The attached
county index map indicates approximate locations for orthophotos at all delivery scales and
for existing horizontal control that is suitable for GPS in and near the County. These maps will
also be available on the following FTP site established by SCGS.
There have been five significant changes have been made to this document since Version 2006.1. They are as follows:
; The Contractor must proof of a license to practice photogrammetric surveying in South
; Auto-correlation during aerial triangulation may be used however, the results must be
verified and sealed by a licensed South Carolina Photogrammetric Surveyor and a
copy of the sealed report supplied to SCGS.
; It is realized that sheet centered imagery may not be economically realized or in the
Counties best interest when utilizing a digital camera, however, the final product
obtained from digital camera imagery must be free of any distortions or inaccuracies
that would normally be avoided when using a film based camera and sheet centered
; A DTM/DEM captured wholly or in part from autocorrelation may be utilized for this
project; however, the contractor will provide a written and sealed statement by a
licensed South Carolina Photogrammetric Surveyor attesting to the accuracy of the
; Any contractual modifications to these specifications and/or any deviation from these
specifications (unless specifically authorized in writing by the contracting officer or an
authorized representative thereof), shall be sufficient cause for rejection of any part or
all of the work performed.
The County will maintain GIS capability using mapping software compatible with the state-mapping program. All deliverables shall be compatible and operational within the County's current system, and shall be deemed unacceptable until compatibility is assured.
The basic specifications as outlined below are designed to obtain digital orthophotos utilizing "traditional" analytical photogrammetric techniques and equipment. The Contractor's Primary proposal must address these specifications as stated herein. The contractor may propose as part of
the primary proposal the use of softcopy photogrammetric techniques and equipment that use supervised or operated assisted methods that meet or exceed traditional methods. Nevertheless, the County is also anxious to consider new technology that would provide cost effective alternative methods for obtaining comparable output products and accuracies. We are therefore requesting that the Contractor submit a Secondary proposal (clearly labeled as the Secondary Proposal) as an attachment to the Primary proposal.
Any contractual modifications to these specifications and/or any deviation from these specifications (unless specifically authorized in writing by the contracting officer or an authorized representative thereof), shall be sufficient cause for rejection of any part or all of the work performed.
II. PROJECT PROCEDURES AND REQUIREMENTS
A. GENERAL. For the purpose of this project, a digital orthophoto is a digital image, which has the properties of an orthographic projection. It is developed from a perspective aerial photograph by differential rectification so that the image displacements caused by camera tilt and terrain relief are removed. Scanning a film negative with a precision image scanner creates the digital orthophoto. The scanned file is then digitally rectified to an orthographic projection by processing each image pixel through the appropriate photogrammetric equations. This process requires as input, control points acquired through ground surveys and developed in aerotriangulation; camera orientation parameters; and a Digital Terrain Model (DTM) or a Digital Elevation Model (DEM). To avoid confusion, the following definitions will apply:
1. Digital Terrain Model (DTM) - a rigorous data model which incorporates mass elevation points, spot elevations and breaklines at significant terrain breaks at a density level sufficient to support generation of contours which meet National Standards for Map Accuracy for topographic mapping as well as for planimetric mapping; however, South Carolina requires a planimetric accuracy of 1/40 inch at scale as opposed to the National Mapping Program requirement for planimetric accuracy of 1/30 inch at scale. The testing of the geospatial positional accuracy will conform to the NSDI Geospatial Positioning Accuracy Standards, Part 3: National Standards for Spatial Data Accuracy (FGDC–STD–007.3–1998).
2. Digital Elevation Model (DEM) - a less rigorous data model to be used for the purpose of creating a digital orthophoto which will meet National Standards for Map Accuracy for planimetric features only; however, South Carolina requires a planimetric accuracy of 1/40 inch at scale as opposed to the National Mapping Program requirement for planimetric accuracy of 1/30 inch at scale.
B. CONTROL. It shall be the responsibility of the Contractor to recover and/or establish sufficient horizontal and vertical control to ensure that final products meet or exceed National Standards of Map Accuracy at the desired scales. A map showing location of existing control is included in the Appendix and on the FTP site mentioned in Section I. above. All proposals shall include a copy of this map indicating which existing points will be targeted and where new control will be established and targeted. A detailed explanation of procedures to be used for establishing new control points will also be included with the proposal. It shall be the responsibility of the Contractor
to ensure that all panels are in place (with Company Name/phone number on panel) and identifiable on the photography; and that all panel materials are removed within 10 days of acceptable photography. There will be 50% of the “Recover and Target Existing Control” cost retained until
proof of panel material is removed and confirmed by SCGS. Airborne GPS (AGPS) is acceptable for horizontal control densification in support of planimetric mapping and/or orthophoto production. Horizontal reference for the project will be NAD 1983/2001, S.C. Single Zone State Plane Coordinate
System, with the International Foot (1 foot = 0.3048 meters “exactly”) being used in all conversions.
Vertical reference shall be NAVD 1988.
C. AERIAL PHOTOGRAPHY.
1. Conditions During Photography. It shall be the responsibility of the Contractor to obtain snow-free and leaf-free aerial photography between February 1, 2006 and March 15, 2006. Photography shall be undertaken when skies are clear, free from excessive smoke or haze, and well- defined images can be resolved. The ground shall be free from standing water, and/or snow. Photography shall be flown only during that portion of the day when the sun is 30 degrees or more above the horizon.
2. Camera System. A six-inch focal length precision aerial mapping cameras of equal or greater quality than Wild RC20 shall be acceptable if equipped with a forward motion-compensating device. The camera and all magazines shall meet or exceed the most recent USGS specifications for aerial camera systems. A copy of the calibration report (no more than 3 years old) and a statement regarding the AWAR rating of the proposed camera system shall accompany all proposals - cameras with AWAR rating below 90 are not acceptable. Digital camera technology may
be used in the primary proposal. The camera performance, resolution, calibration and metric accuracy must meet the mapping specifications as stated for film cameras. A complete explanation of the process of capturing the image through final production if different from the standard specifications must be fully explained and justified.
3. Aerial Film. Aerial film shall have a very fine-grain, unexpired emulsion on a dimensionally stable base such as Kodak Aerocolor III 2400, AGFA Aviphot Color X100 PE1, or equivalent. Only one type of film shall be used throughout the entire project unless approved in writing by the County. Specify the type of aerial film to be used in the proposal. Not applicable for digital cameras.
4. Processing. All negatives, diapositives, prints, etc. shall be processed under "clean darkroom" conditions. They shall have fine grain quality, normal density and such tone and degree of contrast that photographic details show clearly in both dark toned and highlighted areas. They shall be free from spots, scratches, chemical stains and other defects that might detract from their usefulness. Not applicable for digital cameras.
5. Flight Lines. Flight lines will be sheet centered and shall contain sufficient forward overlap to ensure that each digital ortho image is (as much as practical) extracted from the centermost portion of a single aerial photograph. Mosaicking portions of multiple photographs to create a single digital orthophoto image will be permitted, particularly if building lean can be eliminated. All proposals shall include a flight line layout for the project on a copy of the attached index map, or equivalent. It is realized that sheet centered imagery may not be economically realized or in the Counties best interest when utilizing a digital camera, however, the final product obtained from digital camera imagery must be free of any distortions or inaccuracies
that would normally be avoided by using a film based camera and sheet centered photography.
6. Re-flights. All re-flights will be at the expense of the Contractor.
1. Equipment. The device used for scanning shall be a precision instrument designed for photogrammetric applications having an aperture capable of producing a scanning resolution of at least 10 microns; a geometric accuracy of 5 microns; and a capability of resolving 256 tonal levels. All proposals shall include a manufacturer’s calibration report for any scanner to be used on the
project. Not applicable for digital cameras.
2. Procedures and Resolution. Negative exposures of the original aerial photography will be scanned. Exposures will be processed and electronically dodged during scanning to ensure that they do not contain out of focus imagery, dust marks, scratches, and discontinuities in tone or other inconsistencies. Final output pixel resolution for each scale of digital orthophotos shall be as follows:
1"=400' scale – 1.0 feet
1"=200' scale – 0.5 feet;
Initial scanning resolution for each scale shall be fine enough to insure the final output pixel resolution for that scale orthophoto. The Contractor shall include a proposed initial scanning resolution in the proposal.
E. ANALYTICAL AERIAL TRIANGULATION
Densification and extension of field control will be permitted by fully analytical aerial triangulation (FAAT) methods and/or softcopy methods that employs qualified operator supervision at all times during the measuring process. The Contractor shall submit a step-by-step narrative of his methodology (including equipment to be used) with the proposal. Full auto-correlation during
aerial triangulation may be used however; the results must be verified and sealed by a licensed South Carolina Photogrammetric Surveyor and a copy of the sealed report supplied to SCGS for inspection.
F. DTM/DEM DEVELOPMENT.
1. Vertical accuracy of the DTM/DEM shall be sufficient to obtain the required vertical and horizontal accuracies of the final deliverable products.
2. The DTM/DEM shall be captured by an experienced instrument operator using fully analytical optical photogrammetric stereo plotters and/or softcopy instrumentation and techniques capable of achieving required accuracies. Each proposal shall include the specific equipment to be utilized in DTM/DEM capture as well as resumes of specific instrument operators to be assigned to the project (not simply a list of all equipment and all personnel).
3. A DTM/DEM captured wholly or in part from autocorrelation may be utilized for this project; however, the contractor will provide a written and sealed statement by a licensed South Carolina Photogrammetric Surveyor attesting to the accuracy of the DTM/DEM.
4. The DTM/DEM shall have a combination of the following - points spaced at regular intervals along a grid; points of significant high or low elevation; and breaklines at significant terrain breaks. It is understood that density of points and the distribution and extent of breaklines is very dependent upon local terrain variations; however, it is requested that each proposal include a basic recommended procedure (minimum grid spacing and standard breaklines features) upon which the project will most likely be based.
1. The rectification process shall involve the solution of the appropriate
photogrammetric equations for each pixel in the output image. It will not be permissible to solve photogrammetric equations at anchor points and then warp the content of the original image between the anchor points.
2. The interpolation (or resampling) of intensity values from the input image to the output image shall be accomplished using the cubic convolution algorithm or equivalent - use of nearest neighbor or bilinear algorithms will not be acceptable.
H. IMAGE QUALITY/RADIOMETRY.
1. Two hundred and fifty-six (256) tonal levels ranging from 0 (black) to 255 (white) of image brightness shall be represented. All intermediate values shall represent continuous color varying uniformly from black to white. There shall be no areas of an orthophoto where the process was incomplete due to image gaps or lack of data.
2. Image quality of the finished digital orthophoto shall be consistent with the requirements in Section II.C.4 and II.D.2 above.
3. All digital orthophotos shall be radiometrically adjusted as necessary so that adjacent digital orthophotos can be displayed simultaneously without an obvious visual edge seam between them. Localized adjustments of the brightness values shall be performed to minimize tonal differences between the join areas. For this adjustment, the orthophoto judged by visual inspection to have the better contrast shall be used as the reference orthophoto. Localized brightness values of the adjacent orthophoto shall be adjusted to that of the reference orthophoto. When possible and feasible, the area adjusted should be bounded by a tonal break ground feature such as a road, field line, shadow line, etc. The radiometric adjustment should not compromise the accuracy, clarity or resolution of the orthophoto.
4. Prior to undertaking full digital orthophoto production, the Contractor shall furnish the SCGS, and the County with sample digital images at all scales to evaluate and accept as examples of overall image quality. The County will select one image each that will become the standard to which all subsequent digital orthophotos will be compared for acceptance/rejection relative to image quality.
I. AREAL COVERAGE.
The geographic extent of each digital orthophoto shall be as follows:
1"=400' scale 10,000' X 10,000'
1"=200' scale 5,000' X 5,000'
Approximate locations of mapping are included on the attached index map of the County. The grid defined tiles will cover the entire county and beyond as needed to achieve full tile coverage. The
digital orthophoto shall contain only the neat image area of the corresponding map unit and there shall be no image overlap between digital orthophotos.
III. DELIVERABLE PRODUCT SPECIFICATIONS
Digital Orthophotos. Negative scale of photography shall not be smaller than 1"=2,000' for the 1": 400' scale orthophotos or 1"=1,000' for the 1": 200' scale orthophotos, respectively. Digital orthophotos will be delivered to the South Carolina Geodetic Survey for quality control (preferably these can be delivered on external USB hard drive, with the contractor being responsible for paying the shipping costs to and from the SCGS office) - paper check plots for orthophotos will not be required. Two final sets of digital orthophotos will be delivered (one set for SCGS) on DVD’s (burned
on single layer DVD’s not Dual Layer unless approved by the county) in .tif image format with .tfw header. Additional header information will be included in accordance with state standards (see attachment A). DVD’s and containers will be labeled in accordance with state standards (see attachment B). Each label will contain the orthoimages sheet numbers contained on that DVD.
DEM/DTM’s. In addition to the image (.tif) and world (.tfw) files, each orthophoto delivery shall include the appropriate DEM/DTM file in .dxf or .shp format labeled with the same file name/number as the corresponding orthophoto.
IV. OWNERSHIP OF MATERIALS
All materials produced as a result of this project including, but not limited to, aerial negatives, diapositives, aerotriangulation data, terrain and elevation models, and control photographs shall become the property of the County. The County may request that the Contractor store these materials at the Contractor's facility at no charge; however, any and all materials shall be returned to the County upon written request.
V. PROJECT SCHEDULE
A. RFP sent to Contractors Specify Date
B. Written Questions due Two weeks after A
C. Proposals due One week after B
D. Contractor Interviews (if necessary) Two weeks after C
E. Contractor selection One week after D
F. Project completion ???? months from collection
VI. OPTIONAL ITEMS
VII. CATEGORIES FOR SUBMITTING COSTS FOR PRIMARY PROPOSAL
Contractors will submit cost breakdowns for professional services on the project as described
in the specifications. If alternative proposals are submitted, Contractors are asked to use a similar
cost breakdown. For purposes of this proposal, the total number of orthophotos will be XXX with YYY at a scale of 1": 400' and ZZZ at a scale of 1"=200'.
PROJECT PHASE COST
RECOVER & TARGET EXISTING CONTROL $_______________
(______) number of points
(50% of this cost will be retained until proof of panel material is removed and confirmed by SCGS)
ESTABLISH ADDITIONAL CONTROL $_______________
(______) number of points
AERIAL PHOTOGRAPHY $_______________
ANALYTICAL AEROTRIANGULATION $_______________
DTM/DEM CAPTURE $_______________
IMAGE SCANNING $_______________
ORTHO RECTIFICATION & FILE GENERATION $_______________
OTHER (DATA ON DVD INCLUDING TAX) $_______________
PERFORMANCE BOND $_______________
TOTAL PROJECT COST $_______________
South Carolina County Digital Orthophoto Projects
Header Record Format
The digital image shall be archived on a suitable storage media with informational records appended
to the TFW file. The informational records shall be written in ASCII nomenclature and shall be
recorded as records one through four. Each ITEM of information shall occupy a separate line(s). The
four informational records shall contain descriptive information about the image data as follows:
ITEM ABBREVIATION EXAMPLE
A. County Name & State LOCATION = XXXXX COUNTY,SC B. Name of firm producing the data PROD BY = Amblypia, Inc. C. Coordinate system COORD SYS = S.C. STATE PLANE D. Datum DATUM = NAD 1983/2001
E. Unit of measure UNITS = International Foot F. Ground coordinates (easting/
Northing) of the digital image:
1. SW corner LLCOORD = E2,360,000 N420,000
2. NW corner ULCOORD = E2,360,000 N430,000
3. NE corner URCOORD = E2,370,000 N430,000
4. SE corner LRCOORD = E2,370,000 N420,000 G. Coordinate based map-submap
number (determined from
coordinate value of the SW
corner of the 1"=400' map) COORD MAP# = 3462-06
H. Sequential map-submap number
(to be provided to contractor
by the county) SEQU MAP#= 187-06
ITEM ABBREVIATION EXAMPLE
A. Date of aerial photography PHOTODATE = 03/06/04 B. Aerial camera type CAMERA = Wild RC-30 C. Aerial Camera AWAR AWAR = 101
D. Aerial Camera focal
length (mm) FL = 152.66
E. Negative scale of aerial
photography (RF) NEG SCALE = 1:24,000 F. Film manufacturer & type FILM = Kodak 2403 G. Identification of source photo
from which the digital image
was derived (roll-flight line-
exposure number) ROLL/FL/EXP# = 02-12-46
ITEM ABBREVIATION EXAMPLE
A. Final output pixel resolution PXL RES = 1 foot
B. Horizontal accuracy (i.e. meets
National Standards of Map
Accuracy at this HZ scale) HZ ACCURACY = 1:4,800
C. Source and Vertical accuracy of DEM DEM = *
ITEM ABBREVIATION EXAMPLE
A. Identification of areas of
missing image data ( this will
be identified by providing the
coordinates which bound the
perimeter of the missing area;
or by “none” if no missing
areas exist) NO IMAGE = NONE
B. Identification of suspect and
void areas in elevation data
used to make the orthophoto
(same as above) NO ELEVATION = NONE
* This portion of the Header is intended as a precautionary statement to the user concerning
the potential for misinterpreting the reliability of the elevation model. The contractor shall provide a
concise statement for insertion at this point in the header record #3, which will be pre-approved by
the County. For example- “The DEM for this project was developed using an analytical stereoplotter
and is intended to support orthophoto production only – it is not suitable for creation of accurate contour mapping.”