Mosaics

Document No:  D12#434482
 
Revision:  4A
 
Date amended:  14-May-2015
The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Nathan Miller by e-mail or on ph (08) 9323-4669.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information herein displayed.

 

Revision Register

 

Ed/Version Number Clause Number Description of Revision Date
 ISSUE 1 ALL  GUIDELINE DEVELOPED  10/06/03 
​2 ​ALL ​Content Cleanup ​04-Feb-2013
​3 ​ALL ​Content Cleanup ​06-Feb-2013
​4 ​Header ​Document Number Changed ​16-Jun-2014
​4A​Header​Guideline introduction amended.​14-May-2015

Table of Content



1 General

Mosaics of aerial photographs are used within Main Roads as presentation tools for meetings, reports, contracts and public presentations.  Mosaics are made by piecing together two or more individual overlapping images to form a single continuous composite picture.  Mosaics can be produced through joining hard copy photographs, or scanning and joining digital photographs to form a continuous digital image (Digital Mosaics).  Mosaics can additionally be produced from satellite imagery.  

Mosaics are quick and relatively inexpensive to produce and have been used for various purposes by project managers to present information at various stages of their project life. 

Digital mosaics have basically replaced the traditional hard copy process of joining together photographs.  Even for the production of mosaics from historical hard copy records, the flexibility and ease of scanning images into a digital format, generally out weighs any quality compromises using negatives to produce images.

​​ Two individual frame of Perth... mosaic_perthleft.JPG

​ mosaic_perthright.JPG

...overlapped and combined...

 

mosaic_perthjoined.JPG

... to form a mosaic.
mosaic_perth.JPG
  

 

2 Advantages and disadvantages of digital mosaics.

The advantages of digital mosaics are; Effective to display broad project outlines.

They are relatively cheap and easy to make.

Title blocks and lettering can easily be added to a digital image. 

Additional copies of the original digital mosaics can be quickly and cheaply produced.

The disadvantages of mosaics are

Joins between consecutive photos will not exactly align.  Detail such as multiple roads will not adjoin along the length of the join between two photographs. Magnification of images will concurrently magnify the misclose between joins.

Mosaics are constructed from photographs and suffer from image displacement and scale variations. Distances, angles and areas will only be approximate and should not be measured from these images.

Digital overlays can be included with digital mosaics but the image will not represent the true position and hence may not align with design overlays.

Scanning resolution will restrict magnification (enlarging areas) on digital mosaics.

A standard for digital images has been created for Main Road products.  Mosaics can be requested from consultants by using a standard mosaic fax and the "67-08-12 Digital Rectified Image Standard".

3 How to order a mosaic

A standard for digital images has been created for Main Roads which includes digital mosaics.  Mosaics can be requested from consultants using a standard mosaic fax which references to the "Digital Rectified Image Standard 67-08-12".  The Senior Mapping Surveyor can provide advice to Main Roads project managers for service providers on digital mosaics and hard copy mosaics. 

A small number of digital mosaics are available to Main Roads project managers  through the photographic library within Main Roads.  Indexes to this library can be sourced through the Senior Mapping Surveyor. 

 

4 Issues to address in ordering a mosaic.

The following items should be addressed before approaching a consultant for mosaic production. Is the SkyView imagery available within MRWA suitable to be used or will the consultant have to source photography from DOLA and process the images?

The approximate scale for the final product.  Mosaics do not have an exact scale.  The approximate final scale and the original photographic scale will address how much detail you will be able to determine on the ground.

The final size of the print.  The size of the print must be taken into account when you are considering the mosaic scale.  The final plot can become unmanageable when the size is too big. (i.e. a plot greater than 2m is difficult to handle and display)  Is the product for display or would it be easier to create a reference booklet?   Can the area be broken into sections if you wish to maintain a large scale?

You must have a small diagram to indicating the area you wish covered.  Preferably A4 in size for faxing purposes.  This is used in collecting base information and providing to the consultant a clear definition of the area to be covered.  It will also determine the final size of your plot

Do you wish to overlay any additional information? For example text, highlight areas, outline project corridors etc. 

Will a consultant need to extract or manipulate any information before using it as an overlay?  What coordinate system are your overlay files in? Are they all in the same system? 

The mosaic should adopt the standard Main Roads format for mosaics and ortho photos.  Refer to 67-08-12 Digital Rectified Images standard or contact the Senior Mapping Surveyor.  

A paper test plot should be requested to check all information before a final plot is printed.  Different grades of plotting media and different types of plotting technology will likewise effect the final presentation.

For a final high quality print, a digital laser plotter using photographic quality paper should be requested.

A copy of all data produced for the mosaic is to be supplied on CD to the Senior Mapping Surveyor for archival purposes.  This enables the image library to be maintained and allows images to be used in future by other Main Roads project managers. 

The Senior Mapping Surveyor can provide advice on techniques and bench mark prices.