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PHOTOMOD Lite Contest

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PHOTOMOD Lite Project Contest

Nomination: Education with PHOTOMOD Lite

Institute name: Faculty of Sciences University of Lisbon. Department of Geographic Engineering,Geophysics and Energy

Contact Person: P.Redweik

Project description: Elaboration of cartographic products by photogrammetry according to the norms of the National Authority for Cartography of Portugal – Instituto Geográfico Português (IGP)

Number of trained students: 20 per year

Specialties: Master of Geographic Engineering, Master of Geographic Information Systems

Courses: Analytical Photogrammetry, Cartographic Production

Number of academic hours of the theory courses: 60 in total (over two semesters: Analytical Photogrammetry and Cartographic Production)

Number of academic hours of the practical courses: 60 in total (over two semesters)

The courseware was created and updated by the teacher and made available weekly on a campus internet platform.

A set of two strips with a total of 14 digital aerial photos of the Campus of the University of Lisbon, obtained in March 2010 with a DMC Intergraph camera (c=120mmm), was used for the project. The calibration parameters were available, as well as GNSS/IMU data of the flight. The photos are property of the University of Lisbon. The scale of the photos is about 1:8000, GSD≈10cm. For the same region a test LIDAR data set with 1m x 1m grid was available.

Ground control was determined by the students during the project by means of GNSS point positioning using a permanent GPS network.

As for the hardware, each student used its own laptop computer (typical configuration: Processor: Centrino, i3, i5. OS: Windows Vista/Windows7). Anaglyph glasses were available for each student.

The training methodology was the so called “hands on”. Each student had one block to be triangulated and later one region to stereo plot. Individual programming tasks were required as home work in order to help understanding what the software does.

The results of exams were very positive, showing the great advantage of using a professional software as PHOTOMOD (even in the light version).

Project workflow: Part 1. Georeferencing the images (15 weeks x 2h)

1. Elaboration of a photo flight scheme over a virtual globe (e.g. Google Earth) for a rectangular region including all the campus. Photo scale, camera, overlapping, strip direction, security margins and vertex coordinates are given. Strip axes and exposure points have to be drawn according to the requirements using standard tools of the virtual globe.

2. Analysis of possible strip partition due to strong relief changes along the strip. This step is realized by observing maximum height in several profiles parallel to the strip axes along the area (by means of implemented tools in the virtual globe) and comparing it to the admissible maximum height that allows to maintain the end lap within tolerable limits.

3. Elaboration of a program in MATLAB for a photo flight plan according to user input (individual homework).

4. Indexing of the aerial photos of the Campus over the virtual globe

Indexing of the block by the limits of the photos on the virtual globe

5. Analysis of the coverage comparing with the requirements for stereo plotting.

6. Choice of ground control points location in the block for georeferencing through aerotriangulation.

7. Ground control points determination by means of GNSS positioning.

8. Elaboration of a database for the GCPs including numeric, textual and pictorial information of the points and search routines

9. Elaboration of a program in MATLAB for spatial resection and intersection (individual homework).

10. Bundle aerotriangulation project in PHOTOMOD Lite:
 10.1 Project definition and photo import for block building
 10.2 Camera definition (DMC) and automatic interior orientation
 10.3 GCPlist- introduction of ground control points coordinates
 10.4 Interactive measuring of GCPs in one photo they appear on. Transfer to neighboring photos with stereo correlation
 10.5 Interactive measuring and stereo correlation of passpoints (in strip) in the 6 von Gruber regions in both strips
 10.6 Interactive measuring and stereo correlation of tie points (inter strip) minimum 2 common points per photo in inter strip connection zone
 10.7 Control of input data through the “Report on Relative Orientation”. Correction of errors

Measuring pass points and tie points

 10.8 Bundle adjustment without additional parameters. Analysis of sigma0 and residuals in GCPs. These should be smaller than the required by IGP for the actual mapping scale
 10.9 Automatic tie point measuring. Repetition of input data control by means of the “Report on Relative Orientation”. Repetition of Bundle adjustment and analysis of results. Comparison with the results from 10.8. Choice of map scales that could be produced using the actual photos and the achieved georeferencing results

11. Direct georeferencing project in PHOTOMOD Lite:
 11.1 New project creation
 11.2 Import of the photo pairs in the corners of the block (with more ground control points for checking )
 11.3 Import of the respective GNSS/IMU data (Exterior Orientation Data List)
 11.4 Direct Georeferencing
 11.5 Control of georeferencing quality through stereo measurement of ground coordinates of check points and statistical comparison of differences to ground determined coordinates. Determination of the mapping scale that could be produced with direct georreferenced photos, according to the tolerances allowed by IGP.

At this stage, the block, georreferenced by Bundle Triangulation, is ready for plotting operations and orthophoto production.

Project workflow: Part 2. Cartographic Products (15weeks x 2h)

1. Preparation of the map sheet for a scale of 1:10 000. Import of a map sheet model from the internet site of the National Authority for Cartography (IGP):
 1.1 Search in the national cartogram for the location and denomination of the actual sheet.
 1.2 Calculation of corner coordinates of the sheet (cartographic and geodetic), coordinates of indexes of cartographic coordinates, calculation of the length of meridian and parallel 15 “ arcs for insertion in the margins (indexes of the geodetic grid), insertion of text in the margins. This task was done in Microstation.
 1.3 Georeferencing the sheet by coordinates of corners.

2. Elaboration of the Object Classifier in PHOTOMOD (Vectors/Create Layer with Classifier) according to the official Object Catalog for the map scale 1.10 000.

3. Division of the block in interest regions for stereo acquisition of information (Vectors/Build Pre-regions). Each student should acquire the cartographic information of a half stereo pair.

4. Stereo acquisition of planimetric elements by selecting the respective code in the Classifier and using the stereo plotting tools.

5. Altimetry acquisition through a digital terrain model (DTM):
 5.1 Automatic acquisition of the primary heights sample (Vectors/Compute Points automatically) starting from a 20m x 20m grid over the active stereo pair
 5.2 Stereo edition of the created sample points in order to guarantee they lie on the ground and not on trees or buildings. Measurement of new points where the sample is sparse
 5.3 Creation of a TIN over the sample (TIN/Create). Edition of the triangles to adjust the network to the ground
 5.4 Creation of a DEM from TIN (DEM/Build/From TIN) with 5m sample distance
 5.5 Generation of contours from the DEM (Vectors/Build Contours/From DEM) with 5m interval as defined by the IGP for the map scale 1:10 000

Steps of the generation of contours for altimetry layer: heights sample, TIN, DEM, contours

6. Generation of a Digital Surface Model (DSM)from LIDAR data:
 6.1 Import of a LIDAR cloud in LAS format (DEM/Load LIDAR Data)
 6.2 Visual analysis of the cloud in a 3D window (Load LIDAR Data/Show)
 6.3 Removal of no-data by selecting the valid data cloud (Load LIDAR Data/Selection)
 6.4 Generation of a DEM with 1m sample distance from the selected point cloud (Load LIDAR Data/Build DEM from Selected Area)

7. Orthophoto and 3D model generation:
 7.1 This has been done in the module PHOTOMOD MOSAIC ( Photomod/ Project/Mosaic) using the 1m DEM from LiDAR data, which is a DSM, and a cell size on the ground of 0.2 m for the orthophoto (Mosaic / Build)
 7.2 Analysis of the orthoimage quality

8. 3D model generation with realistic texture:
 8.1 Again in PHOTOMOD, import of the orthophoto (Service/Load Georeferenced Images)
 8.2 In 3DWindow (Window/3D Window), select the DEM used for the orthophoto and the Model Type Texture. The orthophoto had been projected over the DEM

3D model with photo texture

9. Graphic edition of the stereo plotted information according to the requirements for a map scale of 1:10 000:
 9.1 Export of all planimetric layers to Microstation(3D). Transformation to 2D
 9.2 Encoding of all objects according to the cartographic norms (IGP)
 9.3 Introduction of symbology (cell, linear and areal symbols)
 9.4 Export of contours layer to Microstation(3D)
 9.5 3D edition of the contours. Insertion of labels in the index contour lines. Transformation to 2D
 9.6 Fusion of planimetry file with contours file
 9.7 Edition of the resulting 2D map tile

10. Final product:
 10.1 Fusion of the files from all students
 10.2 Small edition of the tie zones (contours)
 10.3 Integration of all information in the georreferenced map sheet prepared in 1
 10.4 Elaboration of the map legend

 Download a full description of the project (PDF, 2 MB)

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