Example: Change Projection of an Image

In this example we use the Reproject Component command to change the projection of an image from Latitude / Longitude to a custom Orthographic coordinate system centered on Florida.  The image shows raster data showing terrain elevations in a region of Florida.  



We start with the raster data opened in an image window, as seen above.   The data was imported from a format that correctly specified Latitude / Longitude with WGS 84 base as the projection.    We will reproject the data into an Orthographic projection centered upon Florida.



With the focus on the opened Florida image, the Info pane provides useful information about the image, including the coordinate system it uses.   The strange values for Pixel size are sizes in degrees, the units of measure used in the Latitude / Longitude coordinate system.


in the Component tab of the Info pane click the coordinate system picker button for the Florida layer.



 We choose Reproject Component.    Manifold uses the terms coordinate system and projection interchangeably as synonyms.  



In the Reproject Component dialog we click the coordinate system picker button.  



If we wanted to choose one of the listed favorites we could simply click on the favorite desired.  Manifold offers two favorites by default, the Latitude / Longitude coordinate system and the Pseudo-Mercator coordinate system.   Any additional favorites we have added will appear in that list as well.   We can add to, delete from, or modify items in the Favorites list by clicking  Favorites.


In this example, we will specify a custom coordinate system, so we choose More... to launch the full Coordinate System dialog, allowing us to choose a new coordinate system.  



Orthographic projection is readily available in the staggeringly long list of coordinate systems listed in the Standard tab, literally thousands of them, but we would like to define a custom version of Orthographic. 


What is commonly referred to as "Orthographic" is really an infinity of different versions of Orthographic, each of which is centered upon some particular latitude and longitude.   The "Orthographic" listed in the Standard tab is centered at 0 latitude and 0 longitude, which is useful only if we wish to create an azimuthal map centered just off the coast of Africa.  


Our task is to define an Orthographic centered upon a particular latitude and longitude that is approximately the center of Florida.   That is easy to do using a Custom projection: we will click the Custom tab.



The tab launches with the current coordinate system loaded.   Orthographic is found in the list of coordinate systems in the Type box.



We pull down the list and choose Orthographic.



That loads Orthographic projection with default parameters.  We can now customize the projection as desired.



We enter a new name, Florida Orthographic, and we enter 29 for the Center latitude and -82 for the Center longitude.    


The location at 29 degrees North and 82 degrees West is close enough to the center of Florida for our purposes.  We can get that number by hovering the mouse cursor over the center of Florida on any map or display in Manifold.  Orthographic projects the entire hemisphere of the Earth so any center value anywhere near Florida is good enough to provide a nice display of what we would see if we were hovering above the state on the edge of space and looking down at Florida.  


The Name we have specified has no special meaning other than reminding us how we have specified this particular coordinate system.    A good name can help us remember what it is if we choose to add it to our Favorites.   We press OK.



That closes the Coordinate System sub-dialog and puts us back in the Reproject Component dialog where now we see our Florida Orthographic custom coordinate system is set as the new coordinate system.


We leave other options in their default settings, using inverse, bilinear as the Render choice.  We press Add Component.


Reprojecting an image means changing the dimensions and numbers of pixels so the only option is to Add Component, that is, to create a new image and table in the Project that are a copy of the subject image, but reprojected into the new coordinate system.   See the Reprojection Creates a New Image topic for why reprojecting an image changes the number of pixels.



The result is that a new image, called Florida 2 is created in the Project along with a new table, Florida Table 2, that stores the tiles for the new image.


We double-click open the new image.



The new, reprojected image inherits the Style of the original image.  The original image has not been changed in any way.


The Info pane shows the new information, including more sensible Pixel size values, since the new orthographic projection we specified uses meters as units of measure.



In the illustrations above, we show the original Florida image to the right of the Florida 2 image, so we can compare the visual difference between the Orthographic projection, on the left, and Latitude / Longitude, on the right.  The Latitude / Longitude projection shows features stretched out more in horizontal extent at the latitude of Florida, while the Orthographic projection shows the region as it would appear if we were hovering over it at high altitude.  


Image Size - When changing the projection of images Manifold will choose a new size for the reprojected image that approximates the size of the original while providing enough room for necessary pixel interpolations.   See the discussion in the Reprojection Creates a New Image topic.


The image is only a small part of Florida - The image called Florida might seem to be the entire state, but it is just an accident of terrain that the long feature is similar to the shape of the Florida peninsula.  We can create a map using a Bing streets image server as a base layer and the Florida 2 image as a layer.   We see that the example data set shows a region in central Florida near Tampa.



The brighter red colors show slightly elevated terrain that forms a ridge, the Lake Wales Ridge, to the Northwest of Lake Okeechobee.  The branching valley in the lower left corner is the depression of the Peace River drainage basin, extending from Port Charlotte and Punta Gorda to the Northeast .    


Manifold 9 - Re-Project a Shapefile  - New coordinate system dialogs make it easier than ever to reproject data, often in only one click. This video shows how to import a shapefile and then rapidly reproject it into different coordinate systems. We then show how maps reproject their contents on the fly for display and how to exploit that to rapidly show data in different projections.

See Also



Info Pane: Component


Assign Initial Coordinate System


Reproject Component


Sub-pixel Reprojection


Map Projection


Favorite Coordinate Systems


Favorite Base Coordinate Systems


Example: Reproject a Drawing - An essential example on changing the projection of a drawing, either within the drawing itself, or by changing the projection of a map window that shows the drawing and on the fly reprojects the drawing for display.


Example: Adding a Favorite Coordinate System - Step by step example showing how to add a frequently used coordinate system to the Favorites system.


Example: Style Properties in the mfd_meta Table


Reprojection Creates a New Image - Why changing the projection of an image creates a new image.


About Coordinate Systems


Projections Tutorial