# Presentation: 198574

## Building Base Maps

## Managing large image collections

**Large images can easily exceed the 2-GB limit on file size**
**ESRI offers two major ways to manage spatially tiled images**
**Image Catalogs**
**ArcSDE Rasters (has 5 ways to handle, but beyond scope of this class)**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

## Raster (a.k.a Image) Catalogs

**Group of raster files covering a similar theme and sharing coordinate system**
**Often same format and symbology**
**Examples:**
**Map series (DRGs)**
**Orthophotos (DOQs) **

- StreamStats Data Prep Workshop  Oct 21-22, 2003

## Raster Catalogs

**Display multiple rasters without having to merge them into larger rasters**
**Supported very well in ArcView 3 **
**Supported in ArcPlot, but can’t do a transparent NODATA**
**Also supported in ArcMap, but you need a script to do transparent NODATA**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

## Raster Catalogs

**Format: *****any***** table with columns:****IMAGE, XMIN, YMIN, XMAX, YMAX**
**IMAGE is a pathname to the raster**
**Symbology from first raster in catalog**
**ArcObjects Online sample code exists to help in symbolizing catalogs**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

**Notes:**
Can be an INFO table or dBase table. SDE has additional options.

## Working with Image Catalogs

**Prerequisites:**
**Images in supported formats**
**Georeferenced, spatial reference specified in ArcCatalog**
**All images must use the same colormap**
**If overlapping, need a special value for overlaps or NODATA areas**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

## Image Catalog Procedures:DRG Example

**Get DRGs. Best source: NRCS state offices on CD**
**Decide on projection, datum**
**Clip_project_DRG.aml **
**Project if necessary**
**Trim collars**
**Assign spatial reference: BatchRasterSpatialRef.bas**
**Use a system variable for base of paths in image catalog for portablility**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

**Notes:**
NOTE: Make sure all files are not marked Read Only. Also make sure you have write permissions in the folders.

The BatchRasterSpatialRef.bas script assigns a single spatial reference you choose to all images in the selected directory. Attach the script to a button added to the ArcCatalog GUI. 

For more information on the process, see the DrgImageCatalogs.doc file.

## Create Image Catalogs

**Arc CREATECATALOG command**
**Arc ADDIMAGE command**
**Drgcatalog.aml does both, adds all images in a folder to the catalog**
**Folder2ImageCatalog.bas works in ArcCatalog, can do .SID files**
**Other AMLs:**
**copyimagecat.aml (copies images)**
**trimimagecat.aml (deletes images from disk)**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

**Notes:**
Another handy tool you can download from ESRI’s ArcScripts web site is an ArcView 3.x extension that converts an image catalog to a shapefile. It is very handy to have a shapefile of an image catalog, since you can select shapefile features in ArcMap, make a new catalog from the selected records, etc. The copyimagecat.aml and trimimagecat.aml programs above both work off of image-catalog subsets you can make using a shapefile.

## Raster Catalog Pitfalls

**Make sure all files and folders are NOT read-only**
**Do NOT load into ArcMap until you are sure all paths are correct and all images have spatial references**
**If you load it with a bad spatial reference you will never be able to load it correctly**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

**Notes:**
Another pitfall I recently discovered is that ArcMap will not maintain relative paths to point to a raster catalog (in either .dbf or INFO format). This is a bug in ArcMap.

Note you can put relative paths in the raster catalog, but these need to be relative to where the MXD file is, not where the raster catalog file is. 

## Changing Symbology for an Raster Catalog

**No Symbology tab**
**There’s no way to store a transparent color in a TIFF colormap**
**Must use a script to get a ‘renderer’ from one image, apply it to all**
**ChangeCatalogSymbology.bas**

- StreamStats Data Prep Workshop  Oct 21-22, 2003

**Notes:**
See instructions on installing the ChangeCatalogSymbology.bas script in the file ChangeCatalogSymbology_install.doc.

Using this script you can change the colormap any way you like, then apply it. For example, you can make the DRG green color (forest) transparent. This often makes a more legible map. You could turn off all colors except blue to see just hydrography features. 

## Other base maps

**NLCD**
**Shaded relief at both 90- and 30-meter resolutions**
**Precip, other layers used**
**Make these TIFFs, they work better in ArcIMS**

- StreamStats Data Prep Workshop  Oct 21-22, 2003