setting spatial reference system

[Anonymous]

One important thing in 2d modelling is setting spatialreference system in Ras mapper. If you have Arcgis version 10 or earlier you can find *.prj files in Gis coordinate directory. If you have the newer version(10.1,10.2), you should go to any shape file properties in arc catalog and choose xy coordinate system and then navigate to the projection which you are looking for. then you need to press add to favorite button on the top right hand side of the window and then click ok. the prj file will be stored in c:/users/”username”/appdata/roaming/esri/desktop10.2/arcmap/coordinatesystem
It should be mentioned that appdata is a hidden directory and you need to make it visible first.
It is better to remove the *.prj file from the path which I mentioned earlier otherwise the Arcgis program may have problem with reading coordinates.
Mike.

[Anonymous]

A typical scenario in which I would like to use RAS Mapper is the following:
1. I have an existing RAS file that is georeferenced.
2. I do not have access to ESRI Arc software.
3. I can download, from the USGS National Map, the DEM for the area that bounds the RAS reaches based on knowing the stream names and other geographic references in GridFloat format that RAS Mapper recognizes.
Questions that arise:
1. How does one find the proper projection to use in RAS Mapper for this scenario?
2. If the RAS geometry and the DEM do not register, that is, overlay (often the case); what should be done?
3. If the extent of the DEM does not cover the extent of the RAS model, but does cover the extent of the 2-D areas, will there be a computational problem?
4. Any suggestions regarding how the proceed with this situation? One approach would be to abandon the existing RAS model and prepare a new one from the DEM. That would usually require merging the low-flow surveyed channel with the DEM.

[cameron]

There is free software called QGIS or GRASS that can be used instead of ArcGIS and has similar features, just not as easy to use.

There is also a website called http://spatialreference.org/ where you can type in the coordinate system the DEM data is in and download a *.prj file (projection file) that HEC-RAS Mapper can read. The USGS National Map website should contain the projection that the DEM is in.

If the DEM does not overlay with the HEC-RAS model, you will need to convert the DEM to the correct coordinate system using software.

If the model only covers the 2D area, the model should be able to create the 2D volume curve data. If you turn off floodplain mapping it may or may not run, I have not tested this yet.

In Mapper you can actually create a surface from either the entire cross-sections or just from the channel (between banks). Once this is created you can than use the cross-section/channel surface and DEM to create one surface in Mapper.

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