Public Lab Research note

Calculating Pixel Resolution

by gonzoearth | May 25, 2011 19:18 25 May 19:18 | #297 | #297

Just a brief note here about determining the pixel resolution for a PLOTS map in the Wilkinson Bay, Louisiana area.

We have a finished map, but need to find the pixel resolution to answer the question: "how big is the real world size of a pixel on our map?"

This can be achieved in different ways. In this case we are going to take 3 separate linear measurements on existing identifiable landmarks within both the new map and a existing base map. The resulting ratios should be similar if the measurements are correct, and provide a ratio of pixels to real world units.

As you can see from the graphic, 3 separate areas have been measured in both the USGS base map and Photoshop. The USGS measurements are in feet, the Photoshop values in pixels. Before we analyze the ratios, the units are converted to metric. Ft * 12 = inches / 2.54 = cm Now the ratio is derived from dividing the cm lengths by the pixel measurements. Our resulting 3 ratios from top to bottom : 4.76 | 4.91 | 4.76 In conclusion, we can say with confidence that this map has a pixel:cm ratio of around 1:4.8


Stewart -- we ought to add this to the curriculum:

In fact, publishing the curriculum as a series of shorter-subject posts makes it manageable for us to tackle as well as more accessible to people in our community, no?

Could we have a section called "multispectral analysis" where we could link to the NDVI page, the video tutorial on NRG in Photoshop, things like that?

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I had the same thoughts and there is no time like the present so I added it, thanks. That kind of grouping sounds great.

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