{"id":75711,"date":"2017-02-23T17:45:47","date_gmt":"2017-02-23T17:45:47","guid":{"rendered":"http:\/\/www.esri.com\/arcgis-blog\/products\/product\/uncategorized\/impervious-surface-mapping-using-pro-1-4-part-1-georeferencing\/"},"modified":"2019-12-16T08:33:52","modified_gmt":"2019-12-16T16:33:52","slug":"impervious-surface-mapping-using-pro-1-4-part-1-georeferencing","status":"publish","type":"blog","link":"https:\/\/www.esri.com\/arcgis-blog\/products\/analytics\/imagery\/impervious-surface-mapping-using-pro-1-4-part-1-georeferencing","title":{"rendered":"Impervious Surface Mapping using ArcGIS Pro \u2013 Part 1: Georeferencing"},"author":5991,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"_acf_changed":false,"_searchwp_excluded":""},"categories":[23341,22931,23051],"tags":[26401,32911,23371,24651,23391,28881,23081,23101],"industry":[],"product":[36561],"class_list":["post-75711","blog","type-blog","status-publish","format-standard","hentry","category-analytics","category-imagery","category-water","tag-classification","tag-georeferencing","tag-hydrology","tag-image-analysis","tag-spatial-analytics","tag-stormwater","tag-utilities","tag-water-utilities","product-arcgis-pro"],"acf":{"short_description":"ArcGIS Pro combines powerful image processing, analysis and visualization capabilities with a practical user interface to enable efficien...","flexible_content":[{"acf_fc_layout":"content","content":"

ArcGIS Pro combines powerful image processing, analysis and visualization capabilities with a practical user interface to enable efficient project workflows.\u00a0 The Imagery tab is the home for image processing workflows and tasks, such as georeferencing<\/a> and image classification<\/a>.<\/p>\n

<\/p>\n

The goal of this workflow is to process multispectral imagery to create an impervious surface map of the Gentilly, Louisiana area for storm water management applications. Gentilly is an area just north of New Orleans, depicted by the red box on the map.<\/p>\n

\"Gentilly<\/a><\/p>\n

The source image has four spectral bands: near-infrared (NIR), red, green and blue \u2013 red, green and blue bands display the imagery as natural color while NIR, Red and Blue displays the imagery as a color infrared composite image.\u00a0 The infrared band is especially valuable for depicting vegetation and is highly recommended for reliable impervious surface mapping, see overview of the infrared image above. Generally, the hue and saturation of the red indicates the type of vegetation while the brightness of the red indicates relative vegetation health or vigor.<\/p>\n

\"Source<\/a><\/p>\n

Before we classify the image, we need to georeference it to be registered to the existing landbase as described below.<\/p>\n

The workflow is comprised of two parts:
\nStep 1 \u2013 Georeference the data so that it is registered to the landbase.
\nStep 2 \u2013 Classify the image based on an impervious surface classification schema.
\nThe georeferencing portion of the workflow is addressed first in this blog, while the image classification portion is addressed in a subsequent blog.<\/p>\n

Step 1: Georeferencing<\/strong>
\nGeoreferencing is the process of registering your source imagery to a reference image or vector GIS layer; the reference data is often your existing landbase comprised of orthoimagery and related GIS layers.\u00a0 In this example we will register the new source image to an existing orthoimage by matching control points located on ground features visible in both the source image and the reference image; see Overview of Georeferencing<\/a> for more details.
\nThe source image is a high resolution satellite image with coarse georeferencing applied and is misaligned with the landbase.\u00a0 If your imagery is not aligned with your landbase, more accurate georeferencing is a vital first step for your project. Georeferencing will adjust your source imagery to the proper geographic location, scale and orientation to fit with your reference data. Once your source imagery is properly aligned, the data and information extracted from it will also be inherently aligned with the landbase.
\nMost of the work we will be doing is based on the functionality contained on the Georeference<\/strong> tab. We will register the source image to the Imagery Basemap<\/strong>; however, if you have your own orthoimagery basemap, you can use that as your reference image instead.
\nFrom the Map<\/strong> tab, open the Basemap dropdown and select the Imagery basemap.<\/p>\n

\"Image<\/a><\/p>\n

Select the source image you want to georeference in the Contents<\/strong> pane.\u00a0 This activates the Georeference<\/strong> button in the IMAGERY<\/strong> tab.<\/p>\n

\"Georeference<\/a><\/p>\n

Click the Georeference<\/strong> button to display all the georeferencing functionality.<\/p>\n

\"Georeference<\/a><\/p>\n

There are three approaches to georeferencing your source image, an automatic method, an interactive method which gives you more control over the placement of image-to-image control points, and a hybrid method which first automatically georeferences your source image which is then refined by interactively adding more control points to achieve the optimal georeferenced solution.<\/p>\n

\"Auto<\/a>If your source imagery is similar to your reference data in terms of location, seasonality, spectral bands, and resolution, use the Auto Georeference<\/strong> button. This will use an image-to-image cross-correlation technique to match similar ground control points between your source and reference images.\u00a0 The initial approximate placement of your source image onto the reference image will greatly affect the success of the automatic ground control point (GCP) creation.<\/p>\n

If your source image is significantly misaligned with the reference image, or exhibits significant differences in pixel size or seasonality with the reference image, skip the Auto Georeference step and collect ground control points manually as described below.<\/p>\n

\"Add<\/a>Interactively georeference your image by manually creating coincident ground control points in your source image and reference image using the Add Control Points<\/strong> tool.<\/p>\n

When creating control point pairs between your source and reference images, there are several tips to help you perform a good match:<\/p>\n