Photogrammetric Topographic Mapping for Design

What is it?

Photogrammetry uses overlapping aerial photography to compile digital topographic and planimetric mapping. Arrowhead Mapping delivers terrain models, contours, mapped visible features and orthophotos for civil design and agency projects. Steve Dillon, ASPRS Certified Photogrammetrist since 1989, Certificate #790, leads this work. Field ground control is supplied by the client’s surveyor; Arrowhead performs the aerial photography and photogrammetric mapping.

Typical uses

• Grading, drainage and hydrology design
• Housing developments and street improvements
• Schools, colleges and reclamation projects
• Topography and aerial mapping for ALTA/NSPS surveys

Deliverables

Delivered in your coordinate system and CAD standards, ready to drop into design.

Accuracy & standards

• Standard

  Products meet or exceed National Map Accuracy Standards.

• Reporting

  Horizontal and vertical accuracy specified and reported per project.

• Verification

  Field ground control supplied by the client’s surveyor; independent QC review of every stereo model.

• Datums

  California Coordinate System (CCS83 / State Plane) zones and NAVD88 vertical datum, or project-specific / local datums on request.

• Public agencies

  Mapping can follow agency or Caltrans mapping requirements where specified.

• Certification

  Steve Dillon, ASPRS Certified Photogrammetrist since 1989, Certificate #790.

Ground control

1. GC-01 · Targets

   Control points are determined and shown on the supplied map before photography.

2. GC-02 · Survey

   Field ground control is supplied by the client’s surveyor, tied to the required project datum.

3. GC-03 · QA/QC

   Independent QC review of every stereo model checks completeness and accuracy; final CAD receives another stereo review.

Aerial vs. ground survey

Aerial mapping complements field measurements supplied by your surveyor. Obscured features and detailed field observations remain with that team.

Mapping for ALTA/NSPS surveys

Arrowhead supplies topography and aerial mapping to the surveyor of record for ALTA/NSPS surveys. Table A Item 5 concerns vertical relief, including the source of information, contour interval, datum and originating benchmark. Define those requirements with the surveyor of record; Arrowhead’s contribution is photogrammetric mapping, not the field land-title survey.

Typical process

1. 01

   Plan to the specification

   Flight plans are designed for the accuracy required by the final map scale and contour specifications. Ground control is supplied by the client’s surveyor; control points are determined and shown on the supplied map.

2. 02

   Acquire and check photography

   Wild RC30 photography uses image motion compensation. Flights take place on clear days with at least 5 miles visibility per FAA flight service, between 10:30 a.m. and 2:30 p.m. Photography is checked for overlap, sidelap, tip and tilt.

3. 03

   Process and scan film

   Film is processed in a Versamat processor and scanned on a Wehrli precision photogrammetric scanner.

4. 04

   Compile and review each stereo model

   Topographic mapping is compiled on Leica/KLT softcopy stereo instruments. Independent QC review of every stereo model checks completeness and accuracy.

5. 05

   Consolidate and review CAD

   A CAD editor consolidates models into a master DTM file and a separate planimetric file. Contours are generated from the DTM, and final CAD is reviewed again on the stereo instrument.

6. 06

   Generate and verify orthophotos

   Black-and-white and color orthophotos are generated from the final DTM, typically at 0.25 ft pixel size, varying with project size. The planimetric file is overlaid on the orthophoto to check horizontal position. Products meet or exceed National Map Accuracy Standards; accuracy is specified per project.

Related experience

• Eastern Transportation Corridor (Route 241)
• San Joaquin Hills Transportation Corridor (Route 73)
• L.A. Metro Rail
• Saddleback College

Frequently asked questions