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content/blog/GPS-EXIF-data-from-photos-decimal-format.md

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+---
+title: "Retreiving GPS data in decimal format from EXIF data in photos"
+date: 2022-06-19T19:01:35-04:00
+draft: false
+tags: []
+math: false
+---
+
+For a new feature that I'm cooking up for my website, I need to grab the GPS information from the EXIF data stored in my images. Luckily, `imagemagick`
+comes to our rescue.
+
+```bash
+identify -verbose $IMAGE_FILE | grep GPS
+```
+
+This will return something like the following:
+```
+exif:GPSAltitude: 1250/100
+exif:GPSAltitudeRef: .
+exif:GPSDateStamp: 2022:06:12
+exif:GPSImgDirection: 137/1
+exif:GPSImgDirectionRef: M
+exif:GPSInfo: 1004
+exif:GPSLatitude: 40/1, 50/1, 1815/100
+exif:GPSLatitudeRef: N
+exif:GPSLongitude: 73/1, 53/1, 3625/100
+exif:GPSLongitudeRef: W
+exif:GPSTimeStamp: 17/1, 32/1, 30/1
+exif:GPSVersionID: ....
+```
+
+To request a specific field, for example Latitude:
+```bash
+identify -format "%[EXIF:GPSLatitude]\n" "$IMAGE_FILE"
+```
+
+As with the verbose flag, it will return the information in degrees format
+```
+40/1, 50/1, 1815/100
+```
+
+The following bash function will take the degrees format and convert
+it to the more common decmial format:
+```bash
+DegreesToDecimal() {
+        L0=$(echo "$1" | cut -d "," -f 1)
+        L1=$(echo "$1" | cut -d "," -f 2)
+        L2=$(echo "$1" | cut -d "," -f 3)
+        echo "scale=6;$L0 + $L1/60 + $L2/3600" | bc
+}
+```
+
+For example:
+```bash
+LAT=$(identify -format "%[EXIF:GPSLatitude]\n" "$IMAGE_FILE")
+LAT_DEC=$(DegreesToDecimal "$LAT")
+echo "$LAT_DEC"
+```
+will output:
+```
+40.838374
+```
+
+We can then package this into a script which will output the latitude, longitude, and altitude (m) of an image in decmial format.
+```bash
+#!/bin/sh
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+show_usage() {
+    echo "Usage: getLLA.sh [imagefile]"
+    exit 1
+}
+
+# Check argument count
+if [ "$#" -ne 1 ]; then
+    show_usage
+fi
+
+# Check that relevant command exist
+if ! command -v identify > /dev/null; then
+    echo "Command identify from imagemagick not found. Exiting..."
+fi
+
+IMAGE_FILE="$1"
+LAT=$(identify -format "%[EXIF:GPSLatitude]\n" "$IMAGE_FILE")
+LAT_DIR=$(identify -format "%[EXIF:GPSLatitudeRef]\n" "$IMAGE_FILE")
+LON=$(identify -format "%[EXIF:GPSLongitude]\n" "$IMAGE_FILE")
+LON_DIR=$(identify -format "%[EXIF:GPSLongitudeRef]\n" "$IMAGE_FILE")
+ALT=$(identify -format "%[EXIF:GPSAltitude]\n" "$IMAGE_FILE")
+
+DegreesToDecimal() {
+        L0=$(echo "$1" | cut -d "," -f 1)
+        L1=$(echo "$1" | cut -d "," -f 2)
+        L2=$(echo "$1" | cut -d "," -f 3)
+        echo "scale=6;$L0 + $L1/60 + $L2/3600" | bc
+}
+
+LAT_DEC=$(DegreesToDecimal "$LAT")
+LON_DEC=$(DegreesToDecimal "$LON")
+ALT_DEC=$(echo "scale=6;$ALT" | bc)
+
+LAT_PREFIX=$([ $LAT_DIR == "S" ] && echo "-" || echo "")
+LON_PREFIX=$([ $LON_DIR == "W" ] && echo "-" || echo "")
+
+echo "$LAT_PREFIX$LAT_DEC"
+echo "$LON_PREFIX$LON_DEC"
+echo "$ALT_DEC"
+```

content/blog/conditional-assignment-bash.md

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+---
+title: "Conditional Assignment in Bash"
+date: 2022-06-19T18:49:47-04:00
+draft: false
+tags: ["Bash"]
+math: false
+---
+
+Many programming languages include an quick way to perform a
+conditional assignment. That is, assigning a variable with a value
+based on some condition. Normally this is done through a ternary
+operator. For example, here is how to write it in Javascript
+
+```javascript
+age = 16;
+ageType = (age > 18) "Adult": "Child";
+```
+The variable `ageType` is dependent upon the value of `age`. If it is above 18 then `ageType = "Adult"` otherwise `ageType = "Child"`.
+
+A more verbose way of accomplishing the same thing is the following:
+```javascript
+if (age > 18) {
+    ageType = "Adult"
+} else {
+    ageType = "Child"
+}
+```
+
+How do we do conditional assignment in Bash? One way is to make use of subshells and echoing out the values.
+
+```bash
+AGE_TYPE=$([ $AGE -gt 18 ] && echo "Adult" || echo "Child")
+```
+A common programming feature called *short-circuiting* makes it
+so that if the first condition (`[ $AGE -gt 18 ]`) is false, then it
+will skip the right side of the AND (`&&`) expression. This is because
+`False && True` is always `False`. However, `False || True` is equal
+to `True`, so the language needs to evaluate the right part of an
+OR (`||`) expression.