IMAGINE Discussions

Discuss and share topics of interest using ERDAS IMAGINE the world’s leading geospatial data authoring system.
Showing results for 
Search instead for 
Do you mean 
Reply
Highlighted
Frequent Contributor
Posts: 89
Registered: ‎01-04-2017
Accepted Solution

How to use/exploit Orthorectified imagery

Hi,

 

I have an Orthorectified imagery consisting of two files: "xyz.dgn" and "xyz.tif" I would like to know how to use the orthorectified imagery in ERDAS for the following tasks:

 

  1. Height enquiry of each pixel ?
    1. I have defined elevation sources the same orthorectified file "xyz.tif" Is this the correct way ? I am suspecting because because, high mountain areas are shown as low elevation and low plains are shown with high elevation values.
    2. Also In Inquire cursor Elevation Tab it displays "No Elevation Datum" ScreenShot attached.
  2. How can I display the orthorectified image to visualize the topography in 3D.
    1. When I display the orthorectified image in 3D Viewer, I get a message:
      1. "This Image may not display properly. There are no overlapping regions wi the elevation model"
      2. "A geometry layer must be displayed before this data can be viewed properly. Please open a DEM, TIN or a feature layer with geometery properties to display this layer"
        1. Is it necessary to underlay the DEM ? I thought that as elevation values are already inherited in the orthorectified image, the 3D viewer would make use of it. 
        2. I don't have a raster DEM.
          1. Howerver, with the data set of  "Xyx.tif" there is a directory "DEM"  in which a file xyz.xyz has x,y and z coordinates recorded in "text format" with a space between x, y and z values. HOW can I use/exploit this file in ERDAS ?
  3. What is the use of "xyx.dgn" file, how can I use it in ERDAS ?
  4. And can anyone kindly let me knwo, with all the above mentioned data sets, how can I best demonstrate the 3D capabilities of ERDAS ? Which Menus, Tabs, Methods and routings ?
  5. Do I need any additional data other than missing raster DEM to demonstrate the 3D capabilities of ERDAS ?

 

I am using ERDAS 2020 with SP1

 

Thanks and Best Regards,

 

RSGIS

Highlighted
Regular Contributor
Posts: 318
Registered: ‎11-16-2015

Re: How to use/exploit Orthorectified imagery

Hi,

 

You need an elevation model to perform everything that you're asking. An elevation model is a prequesite for orthorectification so perhaps you could use that one if you have it. If not, there are freely available global elevation datasets available for download including SRTM from the USGS. An orthorectified dataset does not inherit height values, it uses height to correct the imagery to the ground.

 

If available, it is best to use VirtualGIS to display data in 3D. If you don't have the Expansion Pack add-on, then Image Drape is your only option.

 

You may be able to convert the xyz data to raster terrain using the Terrain Prep Tool.

 

A .dgn is an Interactive Graphics Design System CAD software vector file or MicroStation CAD software vector file. I think you can read this directly in IMAGINE but it may lose any styling it had. You may want to ask the providor of the data what it is and for what it would be useful.

 

Cheers,

 

Johnnie

 

Highlighted
Frequent Contributor
Posts: 89
Registered: ‎01-04-2017

Re: How to use/exploit Orthorectified imagery

Dear JohnnieJ,

 

Thanks for your quick reply. All is clear, but one doubt I still have is, if the hight values are not inhereted in the orthorectified image, then which height values it is displaying at the bottom of the viewer, when we choose "elevation source" as the "displayed orthorectified image" itself ?

 

Thanks,

 

rsgis

Highlighted
Technical Evangelist
Posts: 1,022
Registered: ‎10-01-2015

Re: How to use/exploit Orthorectified imagery

Hi @rsgis ,

 

The Elevation field of the Status Bar can show elevation from a variety of sources depending on the data displayed. For example, if it is an image geometrically calibrated with a 3D geometry model (such as RPCs) it will show the elevation determined by that geometry model. However most frequently it will be showing the elevation from your Elevation Library. You can left-click on the field to see how it is currently defined and change the options.

 

Your Elevation Library can be configured from the Terrain tab.

 

Hope that helps.

 

Cheers

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial
Highlighted
Frequent Contributor
Posts: 89
Registered: ‎01-04-2017

Re: How to use/exploit Orthorectified imagery

Hi all,

 

From the status bar elevation field, out of variety of sources to select, I have chosen the “displayed orthorectified image” itself as the “Elevation sources”.  

 

Neither I am using any other elevation source (except the displayed orthorectifed imagery), nor I am using elevation library. My suspense is, still why I am able to see the elevations for each pixel?

 

The Image data set is IKONOS and Spot7, we have used RPCs and DEM to orthorectify.

 

With Ian.anderson reply, I understand that if RCPs are used, the orthorectified image show the elevation determined by the geometry model used. So does it means, the elevation is inherited in the orthorectified image ? (Because there is no any other files, like geometry model etc.,  expect the .img (Orthorectified) and  .rrd file.

 

Howerver, JohnnieJ mentioned that  orthorectified dataset does not inherit height values.

 

So my confusion remains that,  from where the elevation values are coming ?

 

Thanks and Best Regards,

 

RSGIS

Highlighted
Technical Evangelist
Posts: 1,022
Registered: ‎10-01-2015

Re: How to use/exploit Orthorectified imagery

[ Edited ]

Hi @rsgis 

 

There is no “displayed orthorectified image” option, so I'm assuming you mean that you chose the "Choose Elevation Source" option and specified the ortho image? If so then the "elevations" you are seeing are simply the DN values from band 1. I.e. they are not height values.

 

Check this by bringing up the Inquire Cursor and comparing the two values. 

 

Cheers

 

Ian Anderson
Chief Product Owner, Desktop Remote Sensing
Hexagon Geospatial