09-01-2020 07:23 AM
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:
I am using ERDAS 2020 with SP1
Thanks and Best Regards,
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09-01-2020 10:52 PM
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.
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.
09-03-2020 01:30 AM
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 ?
09-03-2020 05:17 AM
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.
09-14-2020 06:29 AM
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,
09-14-2020 09:58 AM - edited 09-14-2020 09:58 AM
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.