Borstad Associates Ltd. - CSA Outreach Task 1

CSA Outreach Task 1

Project 1. Acquire and print a satellite image of a southern Ontario watershed that looks like a colour air photograph and shows a level of detail equivalent to a 1:50,000 topographic map.

It assumed that the user has access to some raster image editing software. The difficulty and cost of the tasks that follow have been rated: are the easiest, and is the hardest. Data prices ($) are also provided.

Data source: Toporama $0

If one simply needs a “picture” of a given area, one can use the CTI Toporama site. Using the NTS index map to locate the map number (e.g. 031G05 is the 1:50,000 map for Ottawa), one can view a full resolution, colour Landsat-7 image in *.gif format. The projection is geographic (i.e. defined by latitude and longitude). The image does not have the full range of possible colours, nor is it georeferenced so it cannot be used in conjunction with other spatial data.

The image can be saved and opened in Paint Shop Pro (or equivalent) for cutting and pasting specific areas into another file for printing or copying into a Word document.

If the area of interest lies on adjacent images they can be mosaiced by copying and pasting them into a new workspace.

Toporama image for NTS map sheet 031G05

Data source: CanImage $25+taxes

A full colour, pan-sharpened (15 m resolution) image based on a 1:50,000 NTS map sheet can be ordered from CTIS with payment by credit card or account. One can choose either geographic co-ordinates or Universal Transverse Mercator projection (UTM is the projection used in 1:250,00 and 1:50,000 topographic maps). The FTP address for download usually arrives within minutes of confirmation of the order.

The image can be saved and opened in Paint Shop Pro (or equivalent) for cutting and pasting specific areas into another file for printing or copying into a Word document.

If the area of interest lies on adjacent images they can be mosaiced by copying and pasting them into a new workspace.

CanImage image for NTS map sheet 031G05 (UTM projection).
As downloaded, the image is very dark.

CanImage image for NTS map sheet 031G05 after enhancement using PaintShop
Image > Adjust > Brightness/Contrast

Data source: GeoGratis or GeoBase $0

A second approach is to identify the Landsat path and row numbers for the area of interest using http://www.geobase.ca/, download the appropriate 170 x 183 km scene. Click on “data extraction”, product Landsat-7 ortho-rectified imagery, coverage: image, access. The map that appears shows the NTS numbering system and the availability of the requested imagery. For example, clicking on a spot nearest Ottawa on map sheet 031 identifies the path, row and date of Landsat-7 ortho-rectified imagery (e.g. 015029_0100_991101), that can be emailed to your address as zipped file (usually within a few minutes).

Alternatively, knowing the Landsat-7 path, row and date, one can access http://geogratis.cgdi.gc.ca, click on FTP button at the top of the page, FTP GeoGratis Now! at the foot of the page, then in sequence click on: landsat-7; ortho/; geotiff/; utm/; and then select the path/row of interest. One is then shown all TM bands for the that scene (e.g. band 1 for path 15, row 29 on the 1 November, 1999 in UTM zone 18 is 015029_0100_991101_l7_01_utm18.zip)

Once identified, down load and store the required *.tif or *.tfw format TM bands (usually band 1: blue, band 2: green and band 3: red) for the scene of interest (e.g. Ottawa is Path 15, Row 29). Each band is about 55 MB and takes about 6 minutes/band to down load with high speed (define rate?) Internet service.

Using Jasc Paint Shop Pro 8

Creating an RGB (red-green-blue) image in Paint Shop is a very straight forward process. Open each of the downloaded Landsat-7 bands in *.tif format. In the top menu bar go to Colors > Channel Combining > Combine from RGB. A dialog box then appears asking which of the image should be used for which band. USe the image below as a reference, but Band1 is green, Band2 is blue and Band3 should go in the red channel. Press OK and you now have a new RGB image created from the original downloaded greyscale TIF files.

Paint Shop has a number of tools in the top menu under 'Colors > Adjust' for enhancing the resulting colour image. Manipulating the Brightness/Contrast options usually provides good improvements to the imagery with minimal time and effort.

Once imported into Paint Shop, the georeferencing information that accompanied the *.tif file is lost. However, images can be mosaiced in Paint Shop using lake shorelines, road intersections and other recognizable features. This doesn't give perfect results along the seam, but this can only be improved upon by much more expensive image analysis programs. The image analysis route will also retain the georeferencing of the image which is of great benefit when moving to a GIS environment as no image registration would be required.

Using Manifold 5.50

As above, an RGB work area is created and then the RGB bands imported and assigned to the appropriate colour channels.The major difference between Paint Shop and Manifold is that in the latter *.tif files retain their georeferencing information as GeoTiff files.