Tag Archives: orthorectification

Our Changing Landscape – Kemper County Energy Project

Posted on January 5th, 2016

In this monthly feature, we span the globe to examine Our Changing Landscape with time series of medium resolution RapidEye satellite imagery. The RapidEye archive dates back to late 2008 and already contains more than 7 billion square kilometers of data. For January, our focus stays on controversial infrastructure development with a look at the Kemper County Energy Project in Mississippi. The RapidEye Constellation RapidEye is a constellation of five 5-meter medium resolution satellites each offering five spectral bands of information. The RapidEye constellation offers daily revisits to every location on the planet with a huge footprint that is 77-km wide. The data is priced competitively with a starting cost of $1.28 per square kilometer for all five spectral bands – academics do receive discounts. RapidEye adds a fifth band, the red edge, to the ‘traditional’ multispectral set of blue, green, red and near-infrared (NIR). The additional spectral data in the red edge band allows users to extract more useful land ‘information’ than can be from traditional 4-band imagery sources. When RapidEye imagery is ordered as a Level 3A Orthorectified product, images from multiple dates are extremely well registered, making it the ideal data source for Our Changing Landscape. Kemper … testContinue reading

G-FAQ – What is Ground Control? Part II

Posted on November 4th, 2014

In last month’s edition of the Geospatial Frequently Asked Question (G-FAQ), we started our discussion on ground control points (GCPs) and their relationship to orthorectification. Specifically, our focus was on determine the number of GCPs required to create an accurate orthoimage and then selecting the locations for these points. In this edition of the G-FAQ, we conclude the discussion of GCPs by offering tips on collecting them in the field, recording metadata about each and then applying them to your orthoimage. As a quick reminder, our focus in this two-part G-FAQ edition is on these questions: What are ground control points and how do they improve the accuracy of high resolution satellite imagery? How do I decide on the number required and the locations of these ground control points? What best practices should I follow in the field when collecting ground control points? In the October edition of the G-FAQ, we learned that ground control points are locations on the planet with a precisely known X, Y and Z position. When these control points are photo identifiable in high resolution imagery, they can be used to improve the data’s accuracy through orthorectification. Starting in August, we discussed the basics (and … testContinue reading

G-FAQ – What is Orthorectification? Part II

Posted on September 2nd, 2014

In August, we started a discussion on orthorectification in the Geospatial Frequently Asked Question (G-FAQ), and this month we conclude the two-part series. In the first part of the series, the focus was on the basics of orthorectification and how orthorectified data can be differentiated from georeferenced data. In this edition of the G-FAQ, we turn our attention to accuracy testing of orthorectified data. We also investigate RPC files which are often required to orthorectify imagery products. As a quick reminder, we focus on these core questions in this two-part G-FAQ series: What is the difference between georeferenced and orthorectified data? How is orthorectification completed and its accuracy tested? What are RPC files and how are they used in orthorectification? In the August 2014 G-FAQ edition, we learned that georeferenced data has no accuracy guarantee. In order to have this assurance, imagery must be orthorectified; and to orthorectify imagery, you need a minimum of an elevation model and a camera model or rational polynomial coefficients (RPCs). In order to have the highest accuracy possible, you also need ground control points, a topic we will turn our attention to in the next G-FAQ series. For now, we can define ground control … testContinue reading

G-FAQ – What is Orthorectification? Part I

Posted on August 5th, 2014

In this month’s edition of the Geospatial Frequently Asked Question (G-FAQ), we turn our attention to the question of horizontal accuracy in high-resolution imagery products. While it seems like a topic that should be relatively straightforward, surprisingly it is wrought with complexities. Broadly speaking, orthorectification is the process of improving the horizontal accuracy of imagery; and as such, it will be the focus of this two-part series. In this two-part G-FAQ series, we focus on this set of core questions: What is the difference between georeferenced and orthorectified imagery? How is orthorectification completed and its accuracy tested? What are RPC files and how are they used in orthorectification? Before we jump headlong into this two part series on orthorectification, let me frame the discussion a bit. First, my focus here is on high-resolution satellite imagery as that is where my knowledge base lies. While many of the principles discussed here would apply to aerial imagery as well, there are certainly topics relevant to aerial data and orthorectification that will not be covered. Second, my focus is on high resolution data and not on medium resolution data. This is done consciously as many medium resolution imagery products are simply too coarse … testContinue reading

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